DO STRUCTURAL-CHANGES OF T-CELL RECEPTOR COMPLEX OCCUR IN TUMOR-BEARING STATE

T cells in tumor-bearing mice and cancer patients were recently shown to be devoid of CD3-zeta chain, a signal-transducing invariant chain i n T cell receptor (TCR) complex, and p56(lck) tyrosine kinase. In the present study, we investigated the structure and function of TCR compl ex in T cells from BALB/c mice bearing CSA1M fibrosarcoma. The express ions of TCR chains and p56(lck) in a T cell-enriched population from s pleen were analyzed. Almost complete loss of CD3-zeta and p56(lck) was observed in the preparation from tumor-bearing mice as assessed by im munoblotting analysis using whole cell lysates, whereas the amounts of other TCR chains were relatively unchanged. However, these changes we re due to the increase of contaminating Mac-1(+) cells in the spleen o f tumor-bearing mice because: 1) the removal of Mac-1(+) cells led to the restoration of CD3-zeta and p56(lck); and 2) CD3-zeta was clearly present when the preparation was solubilized with ionic detergent, Fc receptor gamma chain detected in the preparation from tumor-bearing mi ce disappeared along with the removal of Mac-1(+) cells, These observa tions were further supported by the finding that addition of Mac-1(+) cells from tumor-bearing mice to normal T cells resulted in loss of CD 3-zeta, leaving CD3-epsilon largely intact. When T cells from tumor-be aring mice were highly purified by depletion of Mac-1(+) cells, these T cells contained normal amounts of CD3-zeta at mRNA, protein, and sur face levels, and expressed the properly assembled TCR complex on their cell surface. Moreover, stimulation of the TCR in these T cells by an ti-TCR antibodies resulted in a comparable Ca2+ mobilization to that o bserved in normal T cells. These results suggest that no structural ch anges occur in TCR complex in our tumor-bearing mice, and that complet e depletion of Mac-1(+) cells in important to assess the structure of TCR complex.