MODULATION OF TCR-MEDIATED SIGNALING PATHWAY BY THYMIC SHARED ANTIGEN-1 (TSA-1) STEM-CELL ANTIGEN-2 (SCA-2)

Thymic shared antigen-1 (TSA-1) is a glycosyl-phosphatidylinositol (GP I)-anchored differentiation Ag expressed on murine lymphocytes, and is identical to stem cell Ag-2 (Sca-2), Using newly established mAb agai nst TSA-1/Sca-2, we have previously shown that surface TSA-1 expressio n is induced upon activation in T cells, and that anti-TSA-1 inhibits IL-2 production induced by anti-CD3 stimulation in T cell hybridomas. In the present study, we have analyzed the functional role of TSA-1 du ring T cell activation using normal T cells, T cell hybridomas, and tr ansfected Jurkat cell lines that expressed either GPI-anehored or tran smembrane form of TSA-1, Anti-TSA-1 inhibited IL-2 production from nor mal T cells stimulated with soluble anti-CD3 plus accessory cells, Ant i-TSA-1 exhibited the inhibitory effect on T cells, but not on accesso ry cells, because anti-TSA-1 inhibited IL-2 production in jurkat cells transfected with TSA-1 cDNA, but not in control transfectant, A trans membrane form of TSA-1 was expressed in Jurkat cells by fusing the ext racellular portion of TSA-1 to the transmembrane and cytoplasmic regio ns of the class I Db, The analysis using this transfectant revealed th at anti-TSA-1-mediated inhibition of IL-2 production did not require t he GPI anchor of TSA-1, Finally, in addition to the inhibition of IL-2 production, tyrosine phosphorylation of CD3 zeta-chains observed foll owing TCR stimulation, one of the important early activation events, w as markedly reduced by anti-TSA-1. These results imply that TSA-1/Sca- 2 plays an important regulatory role in the TCR signaling pathway of a ctivated T cells in addition to its role in T cell differentiation.