Surface and cytoplasmic expression of CD2, CD13, and CD25 antigens in human T lymphotropic virus type I infected cell line. An immunoelectron microscopic study.

Immunoperoxidase electron microscopy revealed intracellular expression of CD2, CD13, and CD25 antigens in a unique human T lymphotropic virus type I infected cell line, TI-CL. This cell line is thought to be derived from cord mononuclear cells in the bifurcation stage of T cell and myelomonocytic lineage, based on cytochemical, immunologic, and molecular genetic analyses. Each antigen expression was observed on the plasma membranes, the cisternae of rough endoplasmic reticulum, and the perinuclear cisternae. Surface and cytoplasmic expression of CD25 antigen in adult T cell leukemia/lymphoma cells have been reported, but similar events concerning CD2 and CD13 antigens have not been described previously. CD13 antigen is a marker of myelomonocytic lineage, and biochemical analyses have demonstrated that monoclonal antibodies belonging to CD13 precipitated two glycoprotein molecules of 130,000 and 150,000 molecular weight and that the former molecule (gp130) is the precursor protein of the latter (gp150). In our findings, CD13-positive reaction in the cisternae of rough endoplasmic reticulum and the perinuclear cisternae may correspond to the precursor protein of CD13. CD2 antigen, a 50 kilodalton sheep erythrocyte rosette receptor protein, is the early T lineage antigen and plays an important role in T cell activation. The detection of CD2 antigen on the cell surface and in the cytoplasm may morphologically confirm that this antigen is synthesized in the cytoplasm and inserted into the plasma membrane.