Quantitation of tumor antigen expression on the surface of malignant line Ib lymphocytes by immuno-electron microscopy.

Malignant line Ib lymphocytes obtained from strain C58/J mice moribund with the syngeneic, transplantable leukemia were examined by transmission electron microscopy. A large, multilobulated nucleus containing a prominent nucleolus was typically viewed. In addition to normal organelles, cytoplasmic elements included frequent intracisternal A-type virions. The cell membrane possessed pseudopodia, and occasionally C-type viruses were noted budding from the plasma membrane. On the basis of complement-mediated antibody cytotoxicity assays with the use of either antiserum against mouse IgM, antiserum against mouse IgG, or antiserum against Thy 1.2 antigen, Ib cells were characterized as T-cells. Similarly, leukemia lymphocytes were lysed by a highly specific rabbit anti-Ib tumor-associated surface antigen (TASA) in the presence of complement. The density and distribution of TASA on malignant lymphocytes were analyzed by immuno-electron microscopy with the use of a bridging technique in conjunction with antiserum against Ib TASA. The following observations were reported after the examination of more than 100 randomly selected Ib lymphocytes: a) The density of the TASA was low, b) the distribution of the TASA was random, and c) no evidence indicated cell cycle-dependent expression of the TASA.