The VP6 Protein of Rotavirus Interacts with a Large Fraction of Human Naive B Cells via Surface Immunoglobulins

Abstract

Immunity to human group A rotavirus (RV), a major cause of viral gastroenteritis in infants, involves B lymphocytes that provide RV-specific antibodies. Additionally, some arguments suggest that naive B cells could be implicated in the first steps of the immune response against RV. The aim of our study was to analyze the interaction of VP6 and VP7 RV capsid proteins with human B cells depending on the immune status of the individual, i.e., naive or RV experienced. For this purpose, a two-color virus-like particle flow cytometry assay was devised to evaluate the blood B-lymphocyte reactivity to VP6 and VP7 proteins from healthy RV-exposed adults, recently infected infants, and neonates at birth. Both VP6 and VP7 interactions with B cells were mediated by surface immunoglobulins and probably by their Fab portions. VP7-reactive B lymphocytes were mainly detected from RV-experienced patients and almost exclusively in the CD27-positive memory cell fraction. Conversely, VP6-reactive B lymphocytes were detected at similar and high frequencies in adult, infant, and neonate samples. In adult samples, VP6 reacted with about 2% of the CD27-negative (CD27 neg ) naive B cells. These results demonstrated that the VP6 RV protein interacted with a large fraction of naive B lymphocytes from both adults and neonates. We propose that naive B cell-VP6 interaction might influence the strength and quality of the acquired immune response and should be considered for elaborating RV vaccine strategies.Human group A rotavirus (RV) is recognized as a leading cause of severe dehydrating diarrhea in young children. The worldwide impact of the disease has led to extensive research to develop RV vaccines (15,16,29). However, RV vaccines only partially achieve protective immunity in humans, as do natural primary exposures. The previously released Rotashield vaccine, which has been withdrawn because of adverse effects, conferred only a 60% level of protection against RV-induced diarrhea (1, 35). The bases underlying the variable efficacy of RV vaccines are unknown. Efforts remain to be made to better understand the protective mechanisms against RV for improving vaccine strategies.RV possesses a triple-layered icosahedral protein capsid, and three of the RV structural proteins (VP4, VP6, and VP7) have important antigenic properties. The intermediate-layer capsid protein VP6 mediates group and subgroup specificity, while the outer-layer proteins VP4 and VP7 mediate serotype P and serotype G specificities, respectively (20). VP6 is the most immunogenic RV protein (20, 34). VP6 does not induce neutralizing antibodies (Abs), although some VP6-specific polymeric immunoglobulins A (IgA) are protective in vivo, probably via transcytosis through epithelial cells (6, 32). VP7 is known as the major antigen inducing neutralizing Abs (20). These Abs can passively protect experimental animals from RV-induced diarrhea (26,30,31). In humans, RV-induced Abs probably play an important role in the resolution of viral infection and against reinfections, as suggest...

Immunodominance of the VH1–46 Antibody Gene Segment in the Primary Repertoire of Human Rotavirus-Specific B Cells Is Reduced in the Memory Compartment through Somatic Mutation of Nondominant Clones

“…We found that the proportion of RV VP6-specific B cells that are memory cells represents a lower frequency and a less frequently isotype-switch phenotype compared with the proportion of randomly selected B cells that are memory cells. This high proportion of naive B cells in virus-specific clones in the circulation during infection, even in adults who likely have a history of many previous RV infections, is curious and unexplained (14,15,17). We showed previously a high frequency of naive B cells in the VP6 repertoire in adults, and a reduced frequency of somatic mutations in VP6-specific IgD Ϫ memory B cells (15,17).…”

“…These findings are in agreement with more phenotypic studies in the literature that suggest RV VP6 is a unique Ag. For example, Parez et al (14) reported that a large fraction of human naive B cells interacts with RV VP6 via surface Igs, and these VP6-reactive B cells were detected at similarly high frequencies in adult, infant, and neonatal samples. In mice, Blutt et al (7) also showed robust activation of naive B cells, but not T cells, in Peyer's patches and mesenteric lymph nodes during early RV infection.…”

“…Given the human RV studies showing a high proportion of naive B cells in the RV-specific circulating repertoire (14), the murine model evidence that a large portion of naive B cells expands in the absence of T cell help (7), and the observation of RV-protective Ab production in the TCR knockout mouse (29), it is intriguing to speculate that induction of RV-specific memory B cells occurs in the absence of efficient Th cell activity. Possibly the induction of RV-specific B cells occurs in a unique intestinal compartment independent of germinal centers, or in a unique cytokine milieu in the intestine.…”

“…VP6 does not induce classically neutralizing Abs; however, VP6-specific polymeric IgA molecules are protective in vivo, likely through inhibition of the transcriptional machinery of RV inside the cell during transcytosis of IgA (12,13). Previous studies have shown that the RV VP6 protein interacted with a large fraction of naive B cells from both human adult and neonatal blood samples, suggesting that the naive B cell-VP6 interaction might influence the strength and quality of the acquired immune response (14).…”

Distribution and phenotype of murine rotavirus-specific B cells induced by intranasal immunization with 2/6 virus-like particles

“…Some of the earlier cells observed here may result from the activation of the IgD + B cell fraction reacting with 2/6-VLP that was detected in NALT and CLN. Such cells present in all the lymphoid tissues analyzed from non-immune mice have already been reported within murine splenic cells [11] and, recently, within human B cells from adults, infants and cord blood, and have been proposed to be responsible for an innate B cell response resulting from the interaction of 2/6-VLP with natural surface anti-VP6 Ab [19,20]. Thus, the high frequency of 2/6-VLP-specific B cells observed here may result from both innate and adaptive B cell responses.…”