Sequential activation of human peripheral lymphocytes displaying two distinct euchrysine binding patterns in PHA-stimulated cultures.

The patterns of supravital staining with euchrysine, a fluorescent dye thought to bind preferentially to membranes of lysosomes and other structures involved in endocytosis, were evaluated sequentially in PHA-stimulated cultures of human unseparated, T and non-T lymphocytes under conditions of a reversible, amethopterine-imposed DNA synthesis block. It was found that type I cells (with a single conglomerate of fluorescent granules, constituting approx. 50% of resting T cells) were almost completely replaced by type III cells (with large conglomerates of coarse granules, typical of lymphocytes undergoing blast transformation) up to the end of second day of culture. Type II cells (with very fine fluorescent granules scattered over the cytoplasms, present in about 50% of T and all non-T lymphocytes) did not initially change their number but later were replaced by type III cells, usually starting from the third day of culture. A hypothesis is discussed according to which only type I cells are primarily responsive to PHA, whereas type II cells require "help" from the former, prior to transition into the proliferative stage.