TCR/CD3 complex is composed of the disulfide-linked TCR-alpha beta heterodimer that recognizes the antigen as a peptide presented by the MHC, and non-covalently paired CD3 gamma epsilon- and de-chains together with disulfide-linked zeta-chain homodimers. The CD3 chains play key roles in T cell development and T cell activation. In the present study, we found nor or extremely lower expression of CD3 epsilon in head- and trunk-kidney lymphocytes by flow cytometric analysis, while CD3 epsilon was expressed at the normal level in lymphocytes from thymus, spleen, intestine, gill, and peripheral blood. Furthermore, CD4-1(+) and CD8 alpha(+) T cells from kidney express Zap-70, but not CD3 epsilon, while the T cells from other tissues express both Zap-70 and CD3 epsilon, although expression of CD3 epsilon was low. Quantitative analysis of mRNA expression revealed that the expression level of T cell-related genes including tcrb, cd3 epsilon, zap-70, and lck in CD4-1(+) and CD8 alpha(+) T cells was not different between kidney and spleen. Western blot analysis showed that CD3 epsilon band was detected in the cell lysates of spleen but not kidney. To be interested, CD3 epsilon-positive cells greatly increased after 24 h in in vitro culture of kidney leukocytes. Furthermore, expression of CD3 epsilon in both transferred kidney and spleen leukocytes was not detected or very low in kidney, while both leukocytes expressed CD3 epsilon at normal level in spleen when kidney and spleen leukocytes were injected into the isogeneic recipient. Lower expression of CD3 epsilon was also found in kidney T lymphocytes of goldfish and carp. These results indicate that kidney lymphocytes express no or lower level of CD3 epsilon protein in the kidney, although the mRNA of the gene was expressed. Here, we discuss this phenomenon from the point of function of kidney as reservoir for T lymphocytes in teleost, which lacks lymph node and bone marrow.
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