In summary, we have shown that human appendix and murine PP B cells, freshly isolated from normal tissue, respond to IL-6 with significant increases in IgA SFC. Further, sIGA+ B cells from appendix express more IL-6R than is seen with B cells isolated from PBMC and spleen. When IgA subclass responses were measured, rhIL-6 induced both IgA1 and IgA2 SFC responses; however, 60-70% of the total response was represented by the IgA2 subclass. Our studies suggest that the human appendix as well as murine PP are enriched sources for sIgA+ B cells which are responsive to cytokines such as IL-6 for induction of IgA plasma cell responses. © 1991 Humana Press Inc.