Production and characterization of murine IgA monoclonal antibodies to the surface antigens of rhesus rotavirus.

Rotavirus is the single most important cause of severe diarrhea in humans and is diffuse in most animal species worldwide, and an understanding of the antigenic properties of the virus is essential to the design of rational vaccine strategies. To better understand the localization of viral epitopes involved in antibody-mediated neutralization of virus infectivity, we have orally immunized mice with live rhesus rotavirus (RRV) and generated a panel of hybridoma cell clones secreting IgA class monoclonal antibodies. A total of 12 neutralizing IgA MAbs to VP4 and VP7 proteins were studied for their epitope specificity and topographical relationships by hemagglutination-inhibition assays, neutralization assays, and competitive-binding assays with previously mapped MAbs. In addition, neutralization-escape virus mutants were selected and gene segments for each variant were cloned and sequenced. Two IgA MAbs were found to be directed to the antigenic region A of the VP7 protein at amino acid 94, and 10 MAbs were directed at the VP8 trypsin cleavage fragment of VP4. Five of the VP4-specific MAbs identified the same neutralization epitope on the RRV VP8 protein, not previously associated with RRV neutralization. All neutralization-escape variants selected by this antibody group contained mutations at amino acids 132- 135 of VP4. One IgA MAb selected for a mutation at amino acid 190 of VP4, and the corresponding viral mutant failed to agglutinate erythrocytes. This MAb mapped to an epitope recognized by 2 additional IgA MAbs. These results suggest that oral immunization of mice with RRV elicits an IgA immune response which is predominantly directed toward antigenic determinants on the VP8 portion of VP4. As a consequence, the route of immunization may alter immunodominant neutralization responses elicited to rotavirus.