On the role of CD26 in CD4 memory T cells.

We studied an in vivo mouse model to evaluate the relationships between CD26--a glycoprotein with dipeptidyl peptidase IV (DPP-IV) activity implicated in the regulation of immune functions--and T cells expressing the effector/memory phenotype CD45RB. We report that CD26 does not define a differentiation stage of CD4 T cells because the density and frequency of CD26 on CD4 T cells from the spleen, inguinal and mesenteric lymph node was similar within the CD45RB+ (naïve) and CD45RB- (antigen primed) subsets. This observation was confirmed using CD4 T cells from a T-cell receptor transgenic (tg) model. CD4 tg T cells specific for ovalbumin (OVA) were adoptively transferred and challenged in vivo with antigen. CD26 expression was the same on naive and antigen-stimulated CD4 T cells. Depleting CD4 T cells with an anti-CD4 antibody preferentially depleted the CD45RB+ subset. In CD4 depleted animals CD26 expression was not altered on the CD45RB- subset but the density of CD26 was marginally increased on the remaining CD45RB+ CD4 T cells. The results suggest that, unlike the human, CD26 in the mouse was not directly linked with T cell activation.