The tumor progression-associated human melanoma antigen P3.58 mediates monocyte-lymphocyte interactions in vitro

The melanoma-associated antigen P3.58 is rarely found on benign proliferating melanocytes but is consistently expressed on advanced malignant melanomas which have a high probability of metastasis. Previous studies have shown that its expression on normal tissues is limited to vascular endothelia and lymphoid follicle germinal centers and that it is also expressed by activated monocytes in vitro. In the studies reported here, anti-P3.58 monoclonal antibodies (mAb) were shown to partially inhibit antigen-specific and anti-CD3-induced T cell proliferation and to completely block a lymphocyte/monocyte clustering which occurs in the absence of added antigen. This inhibition is highly specific for P3.58 mAb and was not affected by mAb directed to major histocompatibility complex or T cell antigens. P3.58 therefore seems to be involved in an antigen-independent attraction or adhesion of lymphocytes. P3.58 is the second example (HLA-DR being the first) of an association between the expression of an immune function-associated molecule and the development of metastatic disease in melanoma.