Interaction of CD5 and CD72 is involved in regulatory T and B cell homeostasis

Regulatory IL-10-producing CD1d(high)CD5(+)CD19(+)B cells and CD4(+)CD25(+)Foxp3(+)T cells have been found to modulate immune responses in autoimmunity, infection, and cancer, but the interaction between these two cell subsets remains unclear. Through cell culture and flow cytometry (FACS), we analyzed the interaction of regulatory T cells (Tregs) and regulatory B cells (Bregs). A neutralizing antibody was used to determine the role of CD5 and CD72 in maintaining regulatory T and B cell homeostasis. We found that CD19(+)CD5(+)CD1d hi Bregs induced expansion of CD4(+)Foxp3(+)Tregs, and CD4(+)CD25(+)Tregs also induced expansion of IL-10-expressing Bregs. Once CD72 or CD5 was blocked, both IL-10-expressing Bregs and CD4(+)Foxp3(+)Tregs were reduced in the different cultures. Finally, FACS analysis demonstrated that Foxp3(+)CD4(+)Treg cells were reduced in CD19(Cre) mice defective of CD5 on the surface of B cells. The study suggests that the interaction of CD5 and CD72 plays a critical role in maintaining regulatory T and B cell homeostasis.