Alteration of cultured lymphocyte mitogens by plant lectins

Human lymphocytes placed in culture for 1 to 4 wk (CL) progressively lose stimulating ability when tested in one way mixed lymphocyte culture (MLC), while other membrane components remain quantifiably the same as fresh lymphocytes (FL), i.e. normal T and B cells, HL A antigens, and normal responses to PHA, Concanavalin A (Con A) and MLC stimuli. In the present work lymphocytes were placed in culture with mitogenic doses of PHA and Con A, and washed aliquots (ML) were studied at weekly intervals in MLC. The peak ³H thymidine uptake of FL or CL in response to PHA or Con A was at 5 days, while the peak MLC response was at 9 days. After 1 and 2 wk in culture ML strongly stimulated autologous responding FL (40X control), with a peak response at 9 days. However, the response of allogenic FL to stimulating ML in MLC was even lower than to stimulating CL, if autologous stimulation of FL by ML was subtracted. Moreover, responding ML were strongly stimulated by autologous FL, but not by autologous CL. In contrast to FL, CL were not stimulated by autologous CL. In contrast to FL, CL were not stimulated by autologous ML. The HL A antigens on ML were clearly identifiable by microcytotoxicity. The ML mitogen was stable after heating at 56° for 1 hr, in contrast to allogenic MLC mitogens. It is concluded that plant lectins can unmask new mitogenic sites on cultured lymphocyte membranes as well as mask existing MLC mitogenic sites, and therefore may have strong effects in altering transplantation immunogenicity.