Serological correlate of protection against norovirus-induced gastroenteritis

Abstract

Background: Norovirus infection is the leading cause of acute nonbacterial gastroenteritis. Histoblood group antigens (HBGAs) are host susceptibility determinants for Norwalk virus (NV) infection. We hypothesized that antibodies that block NV-HBGA binding are associated with protection from clinical illness following NV exposure.

Methods: We developed an HBGA blocking assay to examine the ability of human serum to block the interaction of NV viruslike particles with H type 1 and H type 3 glycans. Serum samples from persons who were experimentally challenged with NV were evaluated.

Results: There was a high correlation between the H type 1 and H type 3 synthetic glycan assays (r = 0.977; P < .001); the H type 1 assay had higher quantitative sensitivity (P < .001). Among 18 infected secretor-positive individuals, blocking titers peaked by day 28 after challenge and were higher for individuals who did not develop gastroenteritis than for those who developed gastroenteritis on days 0, 14, 28, and 180 (P < .05 for each). In addition, 6 of 6 subjects without gastroenteritis had measurable prechallenge blocking titers (>25), compared with 2 of 12 subjects with gastroenteritis (P = .002).

Conclusions: Blocking antibodies correlate with protection against clinical NV gastroenteritis. This knowledge will help guide the evaluation of new vaccine strategies and the elucidation of the nature of immunity to the virus. Trial registration. ClinicalTrials.gov identifier: NCT00138476.

Figure 1. Comparison of H type 1 and H type 3 blocking assays

Fifty-two samples representing different time-points were tested using both HBGA H types. (A) H type 1 BT50s are correlated with H type 3 BT50s (r = 0.977, Spearman correlation, p<0.0001). (B) BT50s for each sample are compared for both H types. Blocking antibody levels using the H type 1 assay were higher than those determined using the H type 3 assay, with 2 exceptions (4%) (p<0.0001, Wilcoxon signed-rank test).

Figure 2. GMTs for BT50s by H type 1 blocking assay

Among persons infected with Norwalk virus, BT50 GMTs were significantly higher (asterisk, p<0.05, Mann-Whitney) at each time-point for those with no GE (n=6) compared with those with GE (n=12). Error bars represent 95% confidence intervals. GE = met clinical definition of gastroenteritis, No GE = did not meet definition of gastroenteritis.

Figure 3. Effect of pre-challenge serum BT50 level (H type 1 assay) on development of gastroenteritis

Pre-challenge serum samples were tested for the 18 infected subjects; 12 met clinical definition of gastroenteritis (GE, triangles), 6 did not meet definition of gastroenteritis (No GE, squares). (A) BT50s, (B) total anti-NV ELISA titers. The two empty triangles in panel A represent detectable BT50s in the GE group, and their respective anti-NV titers are shown in panel B.