Identification and characterization of rat T cell subpopulations expressing T cell receptors α/β and γ/δ

Abstract

Peripheral lymphoid organs of the rat were investigated for the presence of lymphocytes that expressed the pan‐T cell markers CD5 and OX‐52 but not the T cell receptor (TcR) α/β. Two such populations were identified: 2% to 4% of lymphocytes in adult spleen, lymph nodes and peripheral blood are CD5⁺ TcR α/β⁻ and express the OX‐52 antigen at the same density as TcR α/β⁺ T‐cells. About 90% of these cells are CD8⁺. A second population is CD5⁻, CD8⁺ and OX‐52^low. Radioimmunoprecipitation from digitonin lysates of surface‐labeled cells with an anti‐CD3 antiserum showed that the CD5⁺, but not the CD5⁻ population of TcR α/β⁻ cells expresses a CD3‐associated disulfide‐linked cell surface molecule of about 100 kDa apparent mol. mass. Upon reduction, one major band, migrating with 48 kDa was observed. A band of the same size was obtained with an anti‐human δ chain peptide antiserum, indicating that the CD3‐associated non‐TcR α/β molecule is the rat TcR α/δ. Functional assays showed that most, if not all natural killer (NK) cell activity is present in the CD5⁻‐OX‐52^low population. Reactivity to foreign major histocompatibility complex (MHC) antigens in mixed lymphocyte reaction was exclusively found in TcR α/β⁺ splenic T cells. It is concluded that rat α/δ T cells in the spleen do not contain a high frequency of cells with specificity for foreign MHC antigens. The seeding of the periphery with α/β and the presumptive α/δ T cells was followed from birth. Most prominently in the spleen, α/β T cells reached adult levels much later than α/δ T cells. Taken together, these findings demonstrate the expression of the TcR α/δ on a minor population of peripheral rat T cells with the predominant phenotype CD4⁻CD8⁺ that has no NK cell activity when freshly isolated and does not contain a high frequency of alloreactive cells.