Rhesus macaque rectal and duodenal tissues exhibit B-cell sub-populations distinct from peripheral blood that continuously secrete antigen-specific IgA in short-term explant cultures.

It is becoming increasingly obvious that evaluation of a vaccine aimed at preventing HIV infection should include assessment of induced immunity at mucosalsites of viral entry. Among the most salient immune responses are viral-specific antibodies. A recent report on IgA-secreting plasma cells in human duodenalexplants prompted us to examine similar duodenaland rectal biopsies of rhesus macaques, a key animal model for pre-clinical HIV/SIV vaccine studies, and characterize the local resident B-cells. Here we report that non-human primate rectal explants possess similar levels of B-cells as duodenalexplants. We characterize the antibody isotype expression on mucosal memory B-cellsand show for the first time that the B-cell memory subsets of the duodenum and rectum are distinct from those of PBMC, not only by essentially lacking CD27+ cells, as previously reported for uninfected macaques(Titanji et al., 2010), but also in being mostly IgD−. SIV- and SHIV-infected macaqueshad fewer total IgA-secreting cells in rectal tissue compared to naive macaques. As expected, the fractions of B-cells with surface expression of IgA were dominant in the rectal and duodenalexplants whereas in PBMC IgG surface expressionwas dominantamong IgD− B-cells. Mucosalantibody secreting cells were found to be predominantly plasma cells/plasma blasts based on their lack of response to stimulation. Importantly, short-term culture of rectal explants of SIV- and SHIV-positive animals led to secretion of Env-specific IgA into the culture supernatant which could be easily measured by ELISA. Collection of such culture supernatant over several days allows for accumulation of mucosalantibody in amounts that should enable antibody purification, characterization, and use in functional assays. Rectal explants can be readily obtained and unequivocally identify the mucosaltissue as the source of antibody. Overall they facilitate evaluation of mucosalvaccines.