Short-term immunoglobulin A B-cell memory resides in intestinal lymphoid tissues but not in bone marrow of gnotobiotic pigs inoculated with Wa human rotavirus

Immunological memory is important for protecting the host from reinfection. To investigate the development and sites of residence of intestinal memory B cells, and their role in protective immunity to reinfection with an ente ric virus, we assessed the association between memory B cell and antibody-s ecreting cell (ASC) responses and protection using a gnotobiotic pig model for human rotavirus (HRV) infection and diarrhoea. The isotypes, quantities and tissue distribution of rotavirus-specific memory B cells and ASC were evaluated prechallenge (28 and 83 postinoculation days [PID]) and postchall enge (7 postchallenge days [PCD]), using enzyme-linked immunospot (ELISPOT) assay, in gnotobiotic pigs inoculated once with virulent or three times wi th attenuated HRV and challenged at PID 28 with the corresponding virulent HRV. Complete protection against HRV shedding and diarrhoea was associated with significantly higher numbers of immunoglobulin A (IgA) and immunoglobu lin G (IgG) memory B cells and ASC in the ileum of virulent HRV-inoculated pigs at challenge. In contrast, pigs inoculated with attenuated HRV had low er number of IgA and IgG memory B cells and ASC in intestinal lymphoid tiss ues, but higher number in the spleen. The bone marrow had the lowest mean n umbers of IgA and IgG memory B cells and ASC prechallenge in both groups of HRV-inoculated pigs. Therefore, bone marrow was not a site for IgA and IgG rotavirus-specific antibody production or for memory B cells after inocula tion with live rotavirus, from 28 PID up to at least 83 PID. The effect of in vitro antigen dose was examined and it was determined to play an importa nt role in the development of ASC from memory B cells for the different tis sues examined.