Interaction between alpha 1 antitrypsin and lymphocyte surface proteases: immunoregulatory effects.

Alpha 1 antitrypsin (alpha 1-AT) is the major plasma protease inhibitor. Radioiodinated alpha 1-AT binds to human lymphocytes. The binding is fast and reversible, and the cells can be saturated with a maximum of approximately 1.2 x 10(6) molecules of alpha 1-AT per lymphocyte. The receptor for alpha 1-AT is a surface-associated protease. Addition of alpha 1-AT completely inhibits cell surface proteolytic activity. Furthermore alpha 1-AT decreases 3H-thymidine incorporation into lymphocytes stimulated by B or T cell mitogens or by allogeneic cells. Since alpha 1-AT was shown to be produced by activated monocytes and to bind to lymphocytes, it is likely to represent a mediator of monocyte-lymphocyte interactions.