Tissue distribution and molecular profile of a differentiation antigen detected by a monoclonal antibody (345.134S) produced against human melanoma cells

The mouse IgG2a monoclonal antibody (MoAb) 345.134S, secreted by a hybridoma derived from a mouse immunized with cultured human melanoma cells, reacts with an 85,000-dalton glycopolypeptide which is disulfide-bridged to a 30,000-dalton polypeptide having little if any covalently attached carbohydrate. The 115,000-dalton complex is peripheral rather than integral in its association with the plasma cell membrane. Indirect immunofluorescence of cryostat thin sections of human tissues with the MoAb 345.134S showed (1) strong staining of the sebaceous glands and basal layer of normal hyperpigmented skin; (2) weak staining of the basal layer of normal pigmented skin and epithelial cells of the gastrointestinal tract, parotid, renal proximal tubules, thyroid, and urinary bladder; and (3) no staining of melanocytes, mammary gland, lung, brain cortex, or liver. The staining pattern of tissues from a 20-week-old fetus is similar to that of tissues from adults. The MoAb 345.134S stained some cases of virtually all tumors tested, including some derived from normal tissues non-reactive with the antibody; intensity of staining of tumors was in general much greater than in normal tissues. The expression of the antigen detected by MoAb 345.134S in a panel of cultured human tumor cells did not correlate with the expression of other tumor-associated antigens or with HLA-A,B or Ia-like antigens. The MoAb 345.134S can mediate complement- and cell-dependent lysis of cultured human tumor cells. The lack of correlation between the extent of immune lysis and the expression of the antigen detected by MoAb 345.134S as well as the effect of puromycin on antibody-mediated cell-dependent lysis indicated that factors other than antigen density play a significant role in the outcome of immune lytic reactions mediated by this monoclonal antibody.