It is well established that increased numbers of plasma cells occur in the localized tissues of chronic inflammatory diseases such as adult periodontitis, and enzymatic isolation has shown that most B lineage cells produce IgG-subclass with some IgA-subclass responses. It would be of importance to determine if excess production of cytokines in the localized lesion account for these responses and in the present study we have assessed gingival mononuclear cell (GMC) supernatants for cytokines that activate B cells including IL-6R expression and for levels of IL-6 present. Inasmuch as limited numbers (~1 to 3 x 106 cells) of GMC were obtained from surgically removed tissues (~400 mg), we have focused on the analysis of IL-6 production by GMC in this study. Further, initial evidence of additional cytokines that are produced by GMC and induce expression of IL-6R on resting B cells has been obtained. The GMC and PBMC from individual patients were cultured in the presence (or absence) of Con A. Higher levels of IL-6 were produced spontaneously by GMC when compared with Con A-stimulated PBMC. When PBMC cultures were supplemented with GMC supernatants obtained from the same patient, high numbers of spot-forming cells (SFC), mainly of IgG followed by IgA isotype, were seen. The induction of SFC by GMC supernatants was inhibited by incubation with a goat anti-human IL-6 antibody. When the effect of GMC supernatants on subclasses of PBMC SFC was determined, the response was IgG1 > IgG2 > IgG3 = IgG4 and IgA1 > IgA2, a pattern remarkably similar to the distribution of plasma cells in the GMC itself. To assess for cytokines in GMC supernatants that mediated B cell activation, supernatants containing anti-IL-6 were cultured with PBMC or purified B cells for 72 h. This treatment induced small proliferative B cell responses and elevated expression of IL-6R on B cells, but did not induce SFC responses. Further, incubation of B cells with GMC supernatants induced resting B cells (G0/G1) to enter the cell cycle (S and G2/M). Addition of human rIL-6 to these cultures on day 3 restored IgG- and IgA-subclass SFC responses by day 7. Cytokine-induced IL-6R expression also occurred in vivo because freshly isolated GMC expressed high levels of this receptor. These results show that GMC produce cytokines that induce B cell activation including IL-6R expression and secrete IL-6 that regulates B cell terminal differentiation into plasma cells of IgG- and IgA-subclasses. We are currently assessing the cytokines produced by GMC that induce the expression of IL-6R on B cells.