A cytoplasmic human melanoma associated antigen as a marker of activation in lymphoid cells.

A cytoplasmic glycoprotein, originally identified by the monoclonal antibody 465.12S in melanoma tumors, is significantly increased in epithelial cells of different histotype following transformation. In the present study we show that the cytoplasmic melanoma associated antigen (cyt-MAA) is drastically enhanced in lymphoid cells by polyclonal and allogeneic stimulation, as well as by transformation. Normal T-cells with helper and suppressor phenotype are far more susceptible than B-cells to this enhancement. However, among transformed lymphoid cells, the expression of the cyt-MAA does not correlate with lineage, but rather with stage of differentiation. Acute lymphoblastic leukemias represent the only exception, since in these lymphoid malignancies cyt-MAA levels are highly heterogeneous even within groups of phenotypically similar lesions. Thus, the expression of the cyt-MAA is shared by cells of distant embryological origin in early stages of their differentiation and/or during proliferation. Quantitation of the cyt-MAA may provide useful information for the classification of some lymphoid malignancies.