Freshly isolated surface IgA+ (sIgA+) B cells from human gut-associated lymphoreticular tissues (GALT), e.g. the appendix, express high levels of IL6 receptor (IL6R) and respond to IL6 with significant increases in the number of IgA-secreting cells. On the other hand, neither sIgM+ nor sIgG+ B cells from appendix express IL6R. When the effect of IL6 on IgA subclass antibody synthesis was examined, the numbers of both IgA1- and IgA2-producing cells were increased upon incubation of GALT B cells with IL6; however, 60-70% of IgA-secreting cells were IgA2 subclass. Aberrant local production of IL6 can contribute to increased B-cell responses that occur in mucosal inflammation such as gingiva of patients with adult periodontitis (AP). When gingival mononuclear cells (GMC) isolated from AP patients were cultured without any stimulus, GMC spontaneously produced biologically active IL6 which induced peripheral blood mononuclear cells (PBMC) from the same patients to become IgG- and IgA-producing cells. Further, mRNA extracted from GMC possessed high message for IL6. When the expression of IL6R was compared between GMC and PBMC isolated from AP patients, IL6R-bearing cells were only seen in the former population. Thus, a high production of IL6, which have the ability to regulate later stages of IL6R+ B-cell development and to induce them to become Ig-secreting plasma cells and to support plasmacytoma growth, are important immunopathological elements for the induction of the increased B-cell response region in inflamed mucosal tissues. © 1992 Institut Pasteur/Elsevier Paris.