Tumor-bound immunoglobulins: an in vivo phenomenon of masked specificity.

We examined the specificity of the lg "coating" on murine tumor cells grown in vivo. Cells were treated in vitro for release of cell-bound lg from ascites tumors. Such uncoated cells showed an increased expression of tumor-associated antigens and a parallel decrease in intensity of the lg coat, but displayed no changes in the expressions of other normal membrane antigens. This was shown by a complement-dependent cytotoxicity assay and radioimmunoassay. These changes were attenuated if the tumor originated from animals that had been irradiated before tumor inoculation. No alterations were found with corresponding cells propaged in vitro and submitted to the same treatments. Our findings and others suggest tumor-specific antibodies among the lg coats detected on tumor cells grown in vivo.