Cellular origins of human polymeric and monomeric IgA: enumeration of single cells secreting polymeric IgA1 and IgA2 in peripheral blood, bone marrow, spleen, gingiva and synovial tissue.

Using modified ELISA and spot-ELISA, which permit the parallel determination of heavy chain subclass and the presence of covalently linked J chain, we analysed IgA found in cell culture supernatants or secreted by individual cells from peripheral blood, spleen, bone marrow, gingiva and synovial tissue, with respect to its polymeric or monomeric IgA form (pIgA, mIgA) and IgA1 or IgA2 subclass. The ELISA for determination of J chain in tissue culture supernatants was specific and highly sensitive (detection limit in pg). The results demonstrated that IgA1-producing cells predominated in the tissues examined, and that J chain could be detected in association with the majority of IgA1 and IgA2 secreted by individual cells. With respect to the frequency of cells secreting polymeric, J chain-containing IgA, only 20-30% of cells from the bone marrow were engaged in the synthesis of PIgA. In other tissues the frequency of cells secreting pIgA1 and pIgA2 was considerably higher. Peripheral blood mononuclear cells secreting pIgA2 were easily inducible during stimulation with T cell-dependent pokeweed mitogen, whereas Epstein-Barr virus-transformed cells secreted preferentially mIgA1. When the frequencies of pIgA-, pIgA1- or pIgA2-secreting cells (determined by spot-ELISA technique) from different tissues were correlated with the proportion of pIgA to mIgA (and IgA subclasses) secreted in tissue culture supernatants, data obtained suggest that many individual IgA-producing cells could be engaged in simultaneous secretion of mIgA and pIgA.