Membrane alterations in lymphocyte proliferation.

The production of antibody or cell-mediated immunity to foreign antigens requires interaction with the requisite B- or T-lymphocytes. When human lymphocytes encounter antigens or plant lectins, they undergo a series of changes which ultimately result in lymphocyte proliferation and an appropriate immunologic response. Antigens or lectins first attach to specific receptors on the lymphocyte membrane. This attachment is followed by changes in membrane permeability and transport of various nutrients and cations. Some of these changes, such as the increase in the transport of sodium and potassium, are adaptive, maintain the internal cation environment, and permit mitogenesis to proceed. Others such as changes in calcium metabolism appear regulatory rather than adaptive and are closely linked with initiation of proliferation and immunologic response. The lymphocyte, like other mammalian cells, maintains a very low free internal calcium concentration. Changes in internal ionized calcium can regulate secretion, contraction, and cell proliferation. The mechanism of calcium regulation is currently under investigation. Calcium may interact directly with cellular enzymes or regulate lymphocyte metabolism in conjunction with a regulatory calcium binding (modulator) protein, "calmodulin".