Evaluation of the Potential Role of Class II Histocompatibility Antigen HLA-DR in Platelet/Thmor Cell Interaction

It has been reported that HLA-DR Is a potent inducer of thrombin generation. Human colorectal cells (GEO, WiDr, DLD-1, and MIP) that lack the constitutive expression of HLA-DR cause platelet aggregation through a thrombin-dependent mechanism. ileatment with recombinant human @†̃-lnterferon induced the expression of HLA-DR in the GEO, WiDr, and DLD-1 cells, whereas the MIP cell line remained HLA-DR negative. The concurrent analysis of tumor cell/platelet interaction after i-interferon treatment showed a decrease in platelet proaggregating ac tivity of either the responsive GEO (highly expressing HLA-DR) or the unresponsive MIP (lILA-DR negative) cells. Furthermore, the DLD.1 (moderately expressing HLA-DR) cells showed an increase of proaggre gating activity after v-interferon treatment, whereas W1Dr (highly ex pressing HLA-DR) cells did not modify theiractivity. These results suggest a lack of a role of lILA-DR in the in vÃ1⁄4ro platelet proaggregating activity of human colorectal tumor cells.