Dialyzable leukocyte extract induces mast cell secretion

Abstract

Dialyzable leukocyte extract (DLE) transfers the ability to elicit delayed-type hypersensitivity, an action which may be due to components that are antigen specific and those that are nonspecific. In the present study we have found that human DLE is capable of inducing secretion of serotonin and histamine from rat mast cells. Release of mediators was noncytotoxic, dose-dependent, and time-dependent and required energy and calcium. In addition, DLE facilitated mast cell secretion caused by IgE and anti-IgE antibody when mast cells were preincubated in doses of DLE below those capable of causing secretion directly. Similar secretory effects were also observed with purified mast cells, and DLE caused mast cell degranulation in vivo. Fractionation of DLE showed that the mast cell-activating components were mostly in the 500–3500 molecular weight fraction in which other nonspecific activities of DLE have been found, and not in the 3500-10,000 molecular weight fraction in which the ability to transfer antigen-specific delayed reactions has been reported to be found. We suggest that some nonspecific effects of DLE may be due to induction or augmentation of secretion from mast cells, and that in some instances the participation of mast cells in delayed-type hypersensitivity could be mediated by such leukocyte-derived factors.