Release of slow reacting substance (SRS) from human leucocytes by lymphokine.

A human histamine releasing lymphokine (histamine releasing factor, HRF) was studied for its ability to release slow reacting substance (SRS) alongside histamine from human leucocytes. HRF was found to release a substantial amount of SRS from human leucocytes. The SRS was identified by its slow contraction of isolated guinea pig ileum preparation in the presence of atropine and mepyramine, inhibition of this action by the SRS antagonist FPL 55712, the inhibition of its production by eicosa--5, 8, 11, 14--tetraynoic acid (ETYA) but not indomethacin, and a final confirmation by a radioimmunoassay for leukotriene C4 (LTC4). Amounts of SRS ranging from a few nanograms to about 180 ng (eqt LTD4) could be released from 10(8) leucocytes depending on the dose of HRF, and there is a good correlation between the amount of SRS produced and the percentage histamine release accompanying it. These findings suggest that the human lymphokine (HRF) may play an important role in acute hypersensitivity and inflammatory reactions in addition to its traditional role as mediator of delayed hypersensitivity reactions.