amara Sljivancanin Jakovl Tjevic · Jelena Martic · Jelena Jacimovic · Nadja Nikolic · Jelena Milasin ·Tanja Lazi? Mitrovi?

Keywords Genetic · Immunity · Innate · Neonatal sepsis · Polymorphism

tInroduction

Infection, along with preterm birth and low birth weight, is one of the most common causes of newborn morbidity and mortality worldwide [ 1— 3]. It is well known that the immune system is immature after birth, making newborns more vulnerable to diff erent pathogens. Several observational studies have proposed that single-nucleotide polymorphisms (SNPs)in diff erent genes encoding inf lammatory proteins may aff ect sepsis outcomes. Most studies investigating the association between genetics and sepsis have been carried out in the adult population [ 4— 7].

Innate immunity represents one of the crucial pathophysiological mechanisms involved in the newborn’s response to infection, and a great focus has been placed on the association between polymorphisms in genes related to innate immunity and neonatal sepsis. A number of original scientif ic studies have been performed but with inconsistent genotyping results [ 8— 12], probably due to diff erent ethnic backgrounds of the newborns, thus hindering the conclusions.

Def ining the risk factors for the development of sepsis in the f irst 28 days of life is an important topic, particularly due to its impact on neonatal morbidity and mortality rate.Identifying newborns at high risk for sepsis development would lead to better prevention and therapy strategies. Previous meta-analyses investigated the association between SNPs in mannose-binding lectin (MBL) [ 13] and interleukin (IL)-6, tumor necrosis factor alpha (TNF-α) andIL-10genes [ 14] and neonatal sepsis development. Meanwhile,several original studies on this topic have been published[ 10, 15— 21], potentially modifying the conclusions drawn in earlier systematic reviews. There is also increasing interest in investigating the association between other SNPs in innate immunity genes and newborn sepsis [ 8— 12, 19]. Hence, the present paper aimed to comprehensively analyze all available data from published observational studies dealing with the association between 11 polymorphisms in genes responsible for innate immunity [MBL, cytokines (TNF-α,IL-1β,andIL-6), cluster of diff erentiation (CD) 14, toll-like receptors (TLRs), and bactericidal/permeability-increasing protein(BPI)] and the development of neonatal sepsis (proven and clinical).

Methods

Study protocol and registration

This study protocol was registered in the International Prospective Register of Systematic Reviews (PROSPERO)database under the number CRD42021244092. The reporting of this systematic review and meta-analysis followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) [ 22] to ensure transparency and minimize methodological bias.

Review question and eligibility criteria

The study was conducted to answer the following PICOS question (P: population, I: intervention, C: comparison, O:outcome, S: study design): is there an association between innate immunity gene polymorphisms and the development of neonatal sepsis?

All studies with data on the genotype distribution for polymorphisms in innate immunity genes in newborns with and without sepsis were included. Neonatal sepsis represents a pathophysiological response to microorganisms or their virulence factors in the bloodstream during the f irst 28 days of life, yet there is still a lack of a unique def inition of this condition [ 3]. Clinical (probable, possible) sepsis, which occurs more often, implies laboratory parameter alterations, usually C-reactive protein elevation and changes in leukocyte count (increase or decrease in absolute number)and/or presence of nonspecif ic and insensitive clinical signs and symptoms: temperature instability (fever or hypothermia), circulatory dysfunction (tachycardia, bradycardia,hypotension, or a delayed capillary ref ill time), respiratory dysfunction (tachypnea, grunting, cyanosis, apnea, the need for supplemented oxygen, or the need for ventilation), gastrointestinal dysfunction (feeding intolerance, abdominal distention, or bloody stool), and neurological dysfunction(irritability, lethargy, hypotonia, or convulsion). Proven neonatal sepsis was def ined as the presence of clinical signs of sepsis with positive blood culture. The exclusion criteria were review papers, meta-analyses, conference abstracts,book chapters, guidelines, editorials, letters, articles presenting repeated results, case reports, cell culture laboratory studies, and animal studies.

Search strategies

A comprehensive literature search was performed with no language restriction through several databases. To identify relevant studies investigating the association of polymorphisms in innate immunity genes and the development of neonatal sepsis, Clarivate Analytics Web of Science including Web of Science Core Collection, Korean Journal Database, Russian Science Citation Index, SciELO Citation Index) [1980—2021], Scopus [1960—2021], PubMed[1964—2021], and Cochrane Central Register of Controlled Trials [1996—2021] were explored until September 26, 2021.An experienced medical librarian (JJ) and the review team jointly developed the search strategy, and the complete search process is reported following the PRISMA-S guidelines [ 23]. Preliminary searches of the specif ied sources were performed to identify terms and synonyms related to the main concepts of interest and to produce and evaluate various information retrieval strategies, maximize sensitivity, and obtain the best search structure. Depending on the searched database, several combinations of previously identif ied free keywords, relevant controlled vocabulary terms(Medical Subject Headings, https:// www. ncbi. nlm. nih. gov/mesh ), Boolean (AND, OR), truncation (*, $), and proximity (NEAR, W) operators were used. Developed literature search strategies were peer-reviewed by a second information specialist using the Peer Review of Electronic Search Strategies guideline [ 24], whose feedback was included in the f inal database search. The number of identif ied papers and complete search strategies used for all explored sources are given in Supplementary Table 1. Furthermore, complementary searches through Google Scholar? (f irst 100 hits), OpenGrey and other available digital repositories(e.g., Networked Digital Library of Theses and Dissertations, Open Access Theses and Dissertations, DART-Europe E-theses Portal, Opening Access to UK Theses) were conducted to f ind unpublished manuscripts, research reports,conference papers, doctoral dissertations, and other gray literature. Finally, to ensure the reliability of the collected data and the inclusion of important studies that may not have been identif ied through database and gray literature searches,reference lists of included studies and relevant review papers were also considered.

Study selection and data extraction

All literature search results were imported into the Rayyan environment [ 25] for duplicate removal and further examination. Two independent investigators (TSJ and JJ) performed the initial screening of titles and abstracts to identify potential primary studies. Papers not classif ied as eligible were excluded, and full texts of initially selected studies were retrieved for further analysis. In the next stage, two investigators (TSJ and JM) independently assessed the full texts to select the articles of interest. All disagreements over the eligibility of particular studies were resolved by consensus or discussion with a senior investigator (JM).

The selected articles were analyzed, and data were extracted by one reviewer (TSJ) and verif ied independently by a second reviewer (NN). Data extraction was performed using Microsoft Excel? (Microsoft Corporation, USA)and a customized data extraction form developed a priori to cover the main features and relevant information on eligible studies. The f inal data variables required to answer the review questions were as follows: details of the study(f irst author, publication year, country where research was conducted, and study design), genotyping method, sample type used, investigated genotypes, Hardy—Weinberg equilibrium, and information about case and control groups (sample size, types of cases and controls, genotype distribution).Disparities in data extraction were resolved by consensus or discussion with a third investigator (TLM). The authors of primary studies were contacted for missing information and clarif ication when necessary.

Risk of bias assessment

Each study was critically assessed for quality using the STrengthening the Reporting of Genetic Association Studies(STREGA) [ 26] addendum to the Strengthening Reporting of Observational Studies (STROBE) statement [ 27] by two independent investigators (TSJ and JJ). Any disagreements were discussed and resolved by a senior reviewer (JM). The STREGA checklist for cohort, cross-sectional and case—control studies comprises 51 items assessing all relevant parts of the article. The STREGA score was calculated for each study as the number of questions adequately reported in the study divided by the number of applicable questions. Based on the STREGA score expressed as a percentage of criteria fulf illed, studies were categorized into high (＞ 80%), moderate (50%—80%), or low (＜ 50%) reporting quality levels.

Meta-analysis

Data previously extracted from selected studies were analyzed using the Cochrane Collaboration software RevMan(Review Manager, Version 5.4 for Windows, The Cochrane Collaboration, Copenhagen, Denmark). A meta-analysis was conducted if three or more studies reported on the same gene polymorphism. The associations of gene polymorphisms and the development of neonatal sepsis were evaluated by the Cochran—Mantel—Haenszel test to calculate odds ratios(ORs) with 95% conf idence intervals (CIs). Heterogeneity was tested using theI2 index, whereI2 values exceeding 25%, 50%, and 75% were def ined as low, moderate, and high heterogeneity, respectively. The f ixed-eff ects model was applied if there was no signif icant heterogeneity among studies. Otherwise, the results were obtained from a randomeff ects model.

Certainty of evidence assessment

The GRADE (Grading of Recommendations, Assessment,Development, and Evaluation) approach [ 28] was adopted to assess the overall quality of clinical evidence for each outcome by two investigators (TSJ and NN) independently.In case of any disagreement, the third investigator participated in the discussion until consensus was reached (JJ).The certainty of the evidence was assessed according to GRADE’s f ive criteria: risk of bias, inconsistency, indirectness, imprecision, and publication bias. The evidence ratings were classif ied as high, moderate, low, and very low quality of evidence. To judge concerns regarding publication bias and assess small-study eff ects in meta-analyses, a funnel plot was generated for ten or more studies included. Egger's linear regression and Begg's rank correlation methods were used to test the funnel plot asymmetry [ 29, 30]. Evidence of asymmetry, based on aPvalue, was considered signif icant if ＜ 0.1. All analyses were performed using R version 3.6.1(R Core Team, Vienna, Austria) and the R package metaversion 4.11-0.

Results

Study selection

A systematic literature search of databases and additional sources yielded a total of 9428 possibly relevant articles(Fig. 1). Five thousand two hundred and seventy-eight duplicate studies were identif ied and removed from the database. After screening titles and abstracts, 4113 records were excluded based on exclusion criteria, while 37 articles were eligible for full-text evaluation. Finally, three studies were excluded due to inadequate study groups, and one study was excluded due to possible overlapping of participants with another study from the same authors (Supplementary Table 2), resulting in a f inal total of 33 articles qualif ied for inclusion in this systematic review (Table 1, Supplementary Table 3) [ 8— 12, 15— 18, 20, 21, 31— 52].

Quality assessment

According to the criteria def ined in the STREGA statement,the lowest achieved result was 29.79% of the maximum possible score, and the highest was 75%. Two-thirds of the included studies (n= 23) were found to be of moderate quality, while the remaining were of low quality (n= 10). The complete results of the STREGA assessment are given in Supplementary Table 4.

Meta-analyses of genotype frequencies

The quantitative synthesis regardingMBLgenetic polymorphisms included six studies for culture-proven sepsis [ 9, 15,37, 38, 43, 45] and 11 studies for clinical plus culture-proven sepsis [ 9, 15— 17, 37— 39, 42, 43, 45, 48]. Pooled ORs showed that theMBLgene polymorphisms did not signif icantly aff ect the risk of neonatal sepsis development, either cultureproven [P= 0.07; OR = 1.48 (95% CI 0.96—2.92),I2 = 70%](Fig. 2 a) or clinical plus culture-proven [P= 0.17; OR = 1.22(95% CI 0.92—1.61),I2 = 58%] (Fig. 2 b). Subgroup analysis was performed for studies discussingMBLexon 1 A/O variants and those evaluatingMBLexon 1 A/B variants. No signif icant association was found, except for the two studies onMBLexon 1 A/B variants, suggesting the association of theMBLexon 1 (AB/BB) genetic polymorphism with the risk of culture-proven sepsis [P= 0.02; OR = 2.75 (95% CI 1.18—6.38)], without any heterogeneity (I2 = 0%) (Fig. 2 a).

Due to an insuffi cient number of studies for meta-analysis, we conducted a narrative review regarding the relationship betweenIL-1βpolymorphisms and the development of neonatal clinical plus culture-proven sepsis. The opposite results were reported for all three investigated SNPs. One study revealed thatIL-1βrs1143627 variant homozygosity and allele carriers were associated with early sepsis [ 10],while another study did not f ind any signif icant correlation[ 49]. Khaertynov et al. [ 49] described increased sepsis risk for rs1143634 and no sepsis risk for rs16944 variant genotypes. A previous study on sepsis risk for the rs1143634 SNP failed to reach any signif icant diff erence compared to the control [ 32]. A study from 2020, however, showed a signif icantly increased risk for early sepsis in a variant homozygous for rs16944 [ 50].

Fig. 1 Preferred reporting items for systematic reviews and meta-analyses f low diagram for new systematic reviews which included searches of databases, registers and other sources. a The total number of records identif ied from each database or register searched is given in Supplementary Table 1; b exclusion of records was performed by a human

Table 1 Characteristics of the observational studies included in the systematic review with meta-analysis

Table 1 (continued)

Table 1 (continued)

Figure 3 illustrates the forest plots for associations ofIL-6rs1800795 and culture-proven (Fig. 3 a) [ 8— 10, 18, 21, 31,34, 35, 40 ] and clinical plus culture-proven sepsis (Fig. 3 b)[ 8— 10, 18, 20, 21, 31, 32, 34, 35, 40, 49]. No signif icant associations were observed, and the level of heterogeneity between the studies was substantial (I2 = 76% andI2 = 67%,respectively).

Pooled data from the studies investigating theTNF-αrs1800629 polymorphism [ 8, 10, 21, 32, 33, 36, 44] suggest a lack of association with neonatal sepsis risk, either cultureproven (Fig. 4 a) or clinical plus culture-proven (Fig. 4 b).

No signif icant association was observed betweenCD14rs2569190 and sepsis development (Fig. 5), judging from the pooled results from four studies, with a low and nonsignif icant level of heterogeneity (I2 = 39%) [ 9, 11, 12, 34].

The quantitative synthesis illustrated in Fig. 6 was performed to evaluate the potential association of threeTLRpolymorphisms (twoTLR4and oneTLR2) with the development of neonatal sepsis.TLR4rs4986790 was not associated with either culture-proven (Fig. 6 a) [ 9, 41, 47, 51] or with clinical plus culture-proven sepsis (Fig. 6 b) [ 9, 12, 41,47, 49, 51]. Pooled data from three studies for theTLR4rs4986791 genotype distribution in cases and controls suggest the association of this polymorphism with the increased risk of culture-proven sepsis [P= 0.02; OR = 2.29 (95% CI 1.12—4.40)], without any heterogeneity (I2 = 0%) (Fig. 6 c)[ 41, 47, 51]. However, the same trend was not observed for clinical plus culture-proven sepsis (Fig. 6 d) [ 12, 41, 47— 49,51]. No signif icant association was observed betweenTLR2rs5743708 and clinical plus culture-proven sepsis (Fig. 6 e)[ 47— 49, 51, 52].

No signif icant diff erence was observed from the pooled data for theBPIrs4358188 genotype distribution between cases and controls, as illustrated (Fig. 7), with a notable heterogeneity level between the studies (I2 = 60%) [ 11, 12, 46].

Certainty of the evidence and publication bias

The certainty of evidence per GRADE varied from very low to low, depending on the polymorphism (Supplementary Tables 5 to 12). Very low certainty of evidence indicates that authors have low conf idence in the eff ect estimate, whereas low certainty of evidence indicates that further research is very likely to aff ect authors’ conf idence in the eff ect estimate and that the estimate may change.

The funnel plots presented in Fig. 8 a and b reflect the scatter plots with standard error (Y-axis) and the log of the odds ratio (X-axis) of each included study. The presence of a slight asymmetry may indicate publication bias,although this may have other causes, such as study heterogeneity. However, publication bias was not detected based on statistical tests. ThePvalues of Egger's and Begg's tests were 0.64 and 0.93 for associations ofIL-6rs1800795 and culture-proven sepsis (Fig. 8 a) and 0.71 and 0.78 for associations ofIL-6rs1800795 and clinical plus culture-proven sepsis (Fig. 8 b), respectively, revealing that there was no statistical evidence of publication bias among the included studies and that our results were stable.

Discussion

Gene polymorphisms leading to inadequate expression of inf lammatory proteins might attenuate the capability of neonates to react properly to infections. This meta-analysis focused on the association between polymorphisms in genes encoding pro-inf lammatory proteinsMBL, cytokines (TNFα,IL-1β, andIL-6),CD14,TLRs, andBPIand neonatal sepsis development.

Polymorphisms in exon 1 of theMBL2gene have been correlated with decreased MBL levels [ 13]. A previous systematic review showed that low MBL levels contribute to the pathogenesis of sepsis in infants [ 13]. The results from the current meta-analysis in the proven sepsis group showed borderline signif icance for elevated sepsis risk in carriers of at least one of the threeMBLgene polymorphisms,with almost threefold higher sepsis risk in carriers ofMBLrs1800450 variants, without any heterogeneity (I2 = 0%). The frequency of these SNPs did not diff er when neonates with clinical and culture-proven sepsis were observed together compared to the control. On the other hand, a previous meta-analysis showed a signif icantly higher risk for sepsis development among neonates with theMBLvariant allele[ 13]. Apart from a greater number of included studies in the present meta-analysis, the discrepancy between these two systematic reviews could be due to several reasons. The previous review covered data from Frakking et al. [ 37] that considered only culture-proven early sepsis, while the current meta-analysis included results for suspected and conf irmed sepsis throughout the whole neonatal period. In the earlier meta-analysis, when separate data for proven and clinical sepsis were available, only newborns with cultureproven sepsis were treated as cases, while clinical sepsis patients were part of the control group. These results were pooled together with data from studies having both clinical and proven sepsis as a case group. In contrast, the current systematic review observed two separate outcomes, cultureproven sepsis versus no infection (f irst outcome) and culture-proven plus clinical sepsis versus no infection (second outcome). In everyday practice, newborns with deterioration of laboratory parameters and clinical signs and symptoms for sepsis but without positive blood culture are met more often than neonates with culture-conf irmed sepsis. That is the reason why in the present review, neonates with clinical sepsis were also considered cases.

Fig. 2 Mannose-binding lectin ( MBL) exon 1 genotypes in culture-proven ( a) and clinical plus culture-proven sepsis ( b). CI conf idence interval

The current systematic review estimated neonatal sepsis risk in carriers of threeIL-1βgene SNPs: in intron 5(rs1143634) and in the promoter region (rs1143627 and rs16944). The opposite results were reported for all three investigated SNPs [ 10, 32, 49, 50]. On the other hand, a meta-analysis of adult patients showed a decreased risk for sepsis in rs1143634 variant carriers [ 53]. This is the f irst systematic review investigating the association between rs1143627 and rs16944 SNPs and sepsis. Studies on the adult population showed conf licting results regardingIL-1βrs1143627 and rs16944 polymorphisms [ 54— 57]. The discrepancy between the current f indings in infancy and observational studies on adults suggests that rs1143634,rs1143627 and rs16944 SNPs could play a diff erent role in sepsis pathogenesis depending on patient age and comorbidities, but further studies with a greater number of newborns need to be carried out to obtain a distinct picture.

A present meta-analysis demonstrated thatIL-6gene polymorphism is not a signif icant risk factor for sepsis and conf irmed the earlier f indings for both child and adult sepsis[ 7, 14, 58]. One study from a previous meta-analysis [ 14]on the newborn population was excluded from the present systematic review due to a lack of information regarding genotype frequencies among patients with sepsis. Another study included in the meta-analysis from 2019 [ 7] was also excluded, as the study population was misinterpreted as infants. A meta-analysis from 2020 showed a signif icant correlation between theIL-6174 G/C polymorphism and sepsis in Caucasians and Afro-Americans, but the authors separately observed clinical and culture-proven sepsis [ 58].In addition, they divided the participants according to ethnicity even though the majority of included studies did not precisely mention their ethnic background. Another confounding factor was that the results on neonatal and pediatric populations were pooled together. A study on full-term neonates showed an increased risk for poor sepsis outcome(higher mortality, need for inotropic support, development of disseminated intravascular coagulopathy) [ 18], while a study on preterm infants did not correlate mortality rates withIL-6polymorphism [ 21]. Such f indings draw attention to the need for larger observational studies investigating the association between theIL-6rs1800795 polymorphism, sepsis, and its outcomes among term and preterm newborns separately.

Fig. 3 Interleukin-6 rs1800795 genotypes in culture-proven ( a) and clinical plus culture-proven sepsis ( b). CI conf idence interval, AA African American, C Caucasian

The frequency ofTNF-αgenotypes was not signif icantly diff erent for either primary or secondary outcomes after pooling data from studies investigating the rs1800629 gene polymorphism. Even though this meta-analysis included two more studies regarding the relationship between thisTNF-αSNP and neonatal sepsis, the results conf irmed the f indings from an earlier systematic review [ 14]. A meta-analysis from 2017 showed an increased risk for sepsis development inTNF-αvariant allele carriers [ 59]. However, only four out of 34 included studies were on infants. It seems that theTNF-α308 G/A SNP plays an important role in adult sepsis development rather than in newborns.

Fig. 4 Tumor necrosis factor-α rs1800629 genotypes in culture-proven ( a) and clinical plus culture-proven sepsis ( b). CI conf idence interval,H?rtel 1 cohort I 2003—2008, H?rtel 2 cohort II 2009

Fig. 5 Cluster of diff erentiation 14 rs2569190 genotypes in clinical and culture-proven sepsis. CI conf idence interval

Fig. 6 Toll-like receptor ( TLR) 4 rs4986790 and rs4986791 genotypes in culture-proven ( a, c) and clinical plus culture-proven sepsis( b, d), TLR2 rs5743708 genotypes in clinical plus culture-proven sepsis ( e). CI conf idence interval

The current meta-analysis of four studies on the neonatal population showed no association betweenCD14rs2569190 genotypes and sepsis development. Esposito et al. [ 46] found a signif icantly higher severe sepsis incidence in infant carriers of theCD14159 C/T variant allele, but that study was not included in the present review due to insuffi cient information about genotype frequencies. Recessive homozygotes for the functional SNP in the promoter region of theCD14gene (rs2569190) have higher transcriptional activity and consequently an increased pro-inf lammatory response [ 60].Two previous systematic reviews on the relationship among adult sepsis and theCD14rs2569190 SNP showed opposite results [ 61, 62], which could be due to diff erent inclusion criteria and analysis of available data. The discrepancy among published data imposes the need to conduct more rigorously controlled observational studies to gain better insight into the relationship between the rs2569190 SNP and the risk of sepsis development.

Activation of TLR signaling in sepsis leads to more pronounced inf lammation, organ failure and death [ 63].The association betweenTLRSNPs and susceptibility to sepsis has not been systematically reviewed. Even though an earlier investigation on a European population found that Asp299Gly and Thr399Ile SNPs cosegregate [ 64], the results of the current meta-analysis showed their diff erent inf luences on neonatal sepsis development. Pooled data from observational studies on theTLRrs4986791 polymorphism showed signif icantly increased neonatal sepsis risk in variant carriers with positive blood cultures (0% heterogeneity). The secondTLR4 SNP (rs4986790) failed to show a signif icant correlation with sepsis in either observed outcome. Additionally, none of the 6 studies included in this meta-analysis observed a signif icant association betweenTLR2rs5743708 and clinical plus culture-proven sepsis. However, Schr?der et al. found a signif icantly higher frequency of the rs5743708 polymorphism among whites, pointing to the need for further association studies between this SNP and the incidence of infectious diseases, especially those caused by organisms with TLR2 agonists, such as mycobacteria, spirochetes, and Gram-positive bacteria [ 65].

Investigations on diff erent adult populations showed noTLR4rs4986790 association with sepsis risk and its outcome, yet the protein expression levels of TLR4 were signif icantly diff erent between the sepsis and control groups[ 66, 67]. On the other hand, Nachtigall et al. [ 68] described a shorter time to onset of severe sepsis or septic shock for bothTLR4andTLR2SNPs and a prolonged length of intensive care unit stay in theTLR4group compared with the wild-type group.

Polymorphonuclear production of BPI is increased in sepsis. It plays an important role in moderating the local inf lammatory response and systemic toxicity by selectively binding to the lipopolysaccharide of gram-negative bacteria,thus causing a bactericidal eff ect [ 69]. To date, the most studiedBPIgene polymorphism in sepsis is rs4358188, with inconsistent results related to pediatric and adult populations [ 70, 71]. Meta-analysis, conducted on three studies,showed no elevated sepsis risk regardless ofBPIgenotype.In contrast, Michalek et al. [ 70] found a signif icant predisposition to Gram-negative sepsis and increased risk of death due to sepsis-related complications in children with theBPIrs5743507 GG genotype as well as in children with rs4358188 AG or GG genotypes.

Several studies included in this systematic review investigated the relationship between specif ic microorganisms in sepsis and observed gene polymorphisms, with inconsistent results. Hartz et al. [ 15] described a higher rate of Gramnegative sepsis in variantMBLhomozygotes born between 32 0/7 and 36 6/7 weeks of gestation, while Dzwonek et al.[ 38] did not show a relationship between theMBLgenotype and susceptibility to any specif ic microorganism. A signif icantly increased risk of developing Gram-negative sepsis was shown in carriers ofTLR4rs4986790 alone or with the rs4986791 variant allele [ 47], theIL-1β31C variant allele[ 49] and in newborns withBPIrs1341023 CC and CT genotypes [ 46]. While one study described [ 9]an increased sepsis rate caused by Gram-positive bacteria in carriers of the homozygousIL6174G mutation, another two studies failed to reach this signif icance [ 32, 35]. In contrast, Baier et al.[ 34] showed an increased risk for fungal sepsis in Caucasian infants when using a recessive model. No correlation was found betweenTNF-αrs1800629 [ 32, 33] andIL-1?C3954T[ 32] SNPs and organism-specif ic bacteremia.

Studies that investigatedMBLpolymorphisms [ 15, 42,43] described no relationship with sepsis mortality, while the results regarding sepsis severity were the opposite [ 15, 37,43, 48]. One study described [ 18] an increased risk for inotropic support, disseminated intravascular coagulopathy and mortality among theIL-6174CC genotype (andIL-6174C allele). In contrast, other studies did not f ind an association between this polymorphism and sepsis severity and lethal outcome [ 21, 32, 34]. The opposite results were also found forTNF-α,CD14rs2569190,TLR4rs4986790, andTLR4rs4986791 SNPs and complications related to sepsis [ 12, 32,33, 46, 51]. The fatal sepsis outcome was not associated withIL-1rs1143634 [ 32] andBPIrs4358188 polymorphisms[ 12] but was correlated with theIL1B511AA genotype [ 50].

Investigation of inf lammatory protein gene polymorphisms could be important due to the potentially impaired ability of their carriers to react adequately to pathogens.Even though this study was conducted systematically and analytically, it has several limitations that should be stressed. A small number of observational studies investigating target gene polymorphisms in neonatal sepsis have been conducted thus far. An evident methodological discrepancy between studies, implicating diff erences in sample size, inclusion criteria for cases and controls, gestational age, birth weight, the def inition of sepsis and time of its onset, failure to match cases and controls according to their age, sex, comorbidities, could also have an impact on the f inal results. Furthermore, the majority of the studies included in this systematic review did not provide precise information about participants’ ethnicity. The certainty of evidence per GRADE was very low or low, suggesting uncertainty in the eff ect estimate, or that further research is very likely to aff ect authors’ conf idence in the eff ect estimate and that the estimate may change.

The present review has, however, some considerable strengths: a priori created and registered protocol in the PROSPERO database, comprehensive literature search of four electronic databases and gray literature without language restriction, literature search and data retrieval process guided by two independent reviewers,with each study critically assessed for quality using the STROBE statement, also conducted by two reviewers separately.

In conclusion, the current systematic review and metaanalysis of 11 polymorphisms in diff erent genes coding for inf lammatory factors revealed a possible association between risk for culture-proven sepsis in newborns only withMBLexon 1 andTLR4rs4986791 polymorphisms.There is an evident need for larger well-designed, multicentric observational studies with a greater sample size and def ined ethnic background to investigate diff erent inf lammatory gene polymorphisms to recognize newborns requiring intensif ied prophylactic measures due to their high risk for sepsis development and poor outcome.

Supplementary InformationThe online version contains supplementary material available at https:// doi. org/ 10. 1007/ s12519- 022- 00569-7.

Author contributionsSJT contributed to conceptualization, data curation, formal analysis, investigation, methodology, project administration, writing of the original draft, reviewing and editing. MJ contributed to data curation, investigation, supervision, validation, writing of the original draft, reviewing and editing. JJ contributed to formal analysis, investigation, methodology, validation, visualization, and writing of the original draft. NN contributed to formal analysis, investigation, methodology, visualization, and writing of the original draft.MJ contributed to investigation, supervision, validation, writing of the original draft, reviewing and editing. LMT contributed to investigation,supervision, validation, writing of the original draft, reviewing and editing. All the authors approved the f inal version of the manuscript.

FundingThis research was supported by the Ministry of Education, Science and Technological Development of Republic of Serbia(No. 451-03-9/2021-14/200129).

Data availabilityAll additional data are available in supplementary material of the manuscript.

Fig. 7 Bactericidal/permeability-increasing protein rs4358188 genotypes in clinical plus culture-proven sepsis. CI conf idence interval

Fig. 8 Funnel plot analysis. a Egger's and Begg's tests for associations of IL-6 rs1800795 and culture-proven sepsis; b Egger's and Begg's tests for associations of IL-6 rs1800795 and clinical plus culture-proven sepsis

Declarations

Ethical approvalNot applicable.

Conflict of interestNo f inancial or non-f inancial benef its have been received or will be received from any party related directly or indirectly to the subject of this article. The authors have no conf lict of interest to declare.