Association of serum anti-gbs2106 protein immunoglobulin G (IgG) in newborns and risk reduction of invasive group B streptococcus disease during early infancy.

Abstract

Background

Human immunoglobulin G (IgG) directed against Group B streptococcus (GBS) epitopes is transferred transplacentally from the mother to the fetus. A GBS putative protein, gbs2106, has been previously identified as a potential GBS protein antigen vaccine candidate. However, its genetic prevalence and surface expression in GBS-isolates has not been evaluated. In this study, we evaluated the prevalence, surface expression and association of maternal-acquired serum anti-gbs2106 IgG in newborns and risk reduction of infant invasive GBS disease through to 90 days of age in a South African-based cohort.

Methods

We conducted a nested case-control study within a previously established birth cohort that was designed to investigate serological markers associated with risk reduction of invasive GBS disease. In the parent study, additional cases were identified through a hospital surveillance system which included infants diagnosed with culture-confirmed invasive GBS disease outside the original cohort study. In this current study, surface expression of gbs2106 was analyzed on recto-vaginal colonizing isolates from mothers whose infants remained healthy, and on isolates from infants who developed invasive GBS disease. Flow cytometry was used to determine surface expression levels. The anti-gbs2106 IgG in maternal and infant or cord blood was measured using a bead-based assay on the Luminex platform.

Results

The gbs2106 gene was present on all colonizing GBS-isolates from women in the control group and infant invasive GBS-isolates. The gbs2106 protein was expressed on 81.6 % (71/87) and 82.2 % (48/58) of maternal colonizing isolates and invasive GBS-isolates, respectively. There was a strong positive correlation (r = 0.855, p < 0.0001) of maternal and cord serum anti-gbs2106 IgG levels, with the combined cord to maternal anti-gbs2106 IgG geometric mean concentration ratio being 0.9 (IQR 0.7–1.1). Serum anti-gbs2106 IgG geometric mean concentrations in the infants were lower among the invasive disease cases (158.7 arbitrary units [AU]/ml; 95 %CI: 102.3–246.2) compared with controls (304.8 AU/ml; 95 %CI: 226.8–409.8; p = 0.012).

Conclusion

Our study demonstrates an inverse association between infant serum anti-gbs2106 IgG and risk of invasive GBS disease, indicating gbs2106 protein as a potential vaccine candidate.