Objective To investigate the effects of B lymphocyte-induced maturation protein-1 ( Blimp-1) on the number and function of splenic lymphocytes.Methods The mice with defective Blimp-1 in T cells were generated by cross-breeding B6.Blimp-1flox/flox mice with B6.Lck-Cre mice.The mononuclear lymphocytes isolated from spleen of T cell conditional Blimp-1 knockout (Blimp-1CKO) mice and wild type ( WT) C57/B6 mice were comparatively analyzed.Alterations of CD4+T and CD8+T cell subsets, the secre-tion of cytokines as well as the expression of C-C chemokine receptor type 7 ( CCR7 ) and Sphingosine-1-phosphate receptor 1 (S1P1) in mice from the two groups were analyzed by flow cytometry.The changes of CD19+B cell subsets were also detected.Results Compared with WT mice, the total numbers of mononu-clear cells, T and B lymphocytes were all significantly increased in Blimp-1CKO mice ( P<0.05) .The ab-solute numbers of CD4+T, CD8+T and CD19+CD5+CD1d+B cells in mice form Blimp-1CKO group were higher than those of the control group (P<0.05), however, no significant differences with the percentages of these cell populations were observed between two groups.Higher numbers and percentages of CD19+CD5+B cells were detected in mice from Blimp-1CKO group (P<0.01).The Blimp-1CKO mice showed increased secretion of IFN-γ, TNF-α, IL-17 and IL-2, but decreased expression of CCR7 on CD8+T cells as com-pared with WT mice (P<0.05).No significant differences with the changes of S1P1 were found between the two groups.Conclusion Blimp-1 played an important role in the maintenance of number, phenotype and function of T cells.Furthermore, not only T cells but also B cell subsets in mice were affected by the dele-tion of Blimp-1 in T cells.