As previously reported by others for immunoglobulin (Ig)G, we observed that IgA can induce interleukin (IL)-10 expression in human monocytes. In this study, we explored the molecular mechanisms of IL-10 induction by IgA in monocytes and monocyte-derived dendritic cells (MD-DCs). Monomeric IgA induced IL-10 production in monocytes and this production was further increased upon IgA cross-linking. Similar IL-10 responses were observed in monocytes and autologous MD-DCs, and were inhibited (by approximately 77%) by preincubation with a blocking mAb to FcalphaRI. IL-10 induction by IgA correlated with activation of MAPKinases ERK1/2, p38 and JNK, whereas only p38-inhibitor SB-203580 inhibited IL-10 induction. Upon IgA stimulation, AP-1, NFkappaB and Sp1 transcription factors were activated and inhibitors of NFkappaB and of Sp1 suppressed IgA-driven transcriptional activation of IL-10. In addition, p38 MAPK activation appeared that it was required to control nuclear translocation of NFkappaB and Sp1 upon IgA stimulation. Therefore, in human monocytes and MD-DCs the mechanisms of IL-10 induction by IgA involve p38 MAPK-dependent recruitment of both NFkappaB and Sp1.