Interleukin (IL)-10 has been shown to have various effects on B cells, including positively affecting the production of immunoglobulin A (IgA) and IgG. Several human IL-10-related molecules have been identified. These include IL-19, IL-20, IL-22, IL-24, IL-26, IL-28 and IL-29. To determine the effects of the IL-10 analogues on the class switch recombination in B cells, we analysed Ig production from naïve B cells stimulated with these cytokines in the presence of anti-CD40. None of the cytokines were found to induce Ig production by themselves in the presence of anti-CD40 Ab. However, all cytokines inhibited the production of IgA and IgG induced by anti-CD40 Ab alone. In combination with anti-CD40 Ab and IL-4, IgG4 were inhibited in cultures stimulated with IL-20, IL-22, IL-26, IL-28 and IL-29 compared with IL-4 and anti-CD40 Ab alone, whereas all IL-10 analogues increased the production of total IgG. All analogues reduced anti-CD40 Ab + transforming growth factor (TGF)-beta-induced IgA production compared with cultures stimulated with anti-CD40 Ab and TGF-beta alone. Together, these data show that the IL-10-related cytokines in combination with anti-CD40 Ab are not by themselves directly involved in the Ig regulation in B cells. However, some of the analogues might have regulatory effects on CSR induced by CD40-ligation in combination with IL-4 or TGF-beta.