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‐ζ chain, a signal‐transducing invariant chain in T cell receptor (TCR) complex, and p56(lck) tyrosine kinase. In the present study, we investigated the structure and function of TCR complex in T cells from BALB/c mice bearing CSA1M fibrosarcoma. The expressions of TCR chains and p56(lck) in a T cell‐enriched population from spleen were analyzed. Almost complete loss of CD3‐ζ and p56(lck) was observed in the preparation from tumor‐bearing mice as assessed by immunoblotting analysis using whole cell lysates, whereas the amounts of other TCR chains were relatively unchanged. However, these changes were due to the increase of contaminating Mac‐1(+) cells in the spleen of tumor‐bearing mice because: 1) the removal of Mac‐1(+) cells led to the restoration of CD3‐ζ and p56(lck); and 2) CD3‐ζ was clearly present when the preparation was solubilized with ionic detergent. Fc receptor γ chain detected in the preparation from tumor‐bearing mice disappeared along with the removal of Mac‐1(+) cells. These observations were further supported by the finding that addition of Mac‐1(+) cells from tumor‐bearing mice to normal T cells resulted in loss of CD3‐ζ, leaving CD3‐ζ largely intact. When T cells from tumor‐bearing mice were highly purified by depletion of Mac‐1(+) cells, these T cells contained normal amounts of CD3‐ζ at mRNA, protein, and surface levels, and expressed the properly assembled TCR complex on their cell surface. Moreover, stimulation of the TCR in these T cells by anti‐TCR antibodies resulted in a comparable Ca(2+) mobilization to that observed in normal T cells. These results suggest that no structural changes occur in TCR complex in our tumor‐bearing mice, and that complete depletion of Mac‐1(+) cells in important to assess the structure of TCR complex.