GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR IS A GROWTH-FACTOR FOR PROMASTIGOTES OF LEISHMANIA-MEXICANA-AMAZONENSIS

ABSTRACT. In this paper we show that murine lung conditioned medium (LCM) displays, in addition to its already described colony‐stimulating activity on bone marrow cells, a potent growth‐stimulating activity on promastigotes of Leishmania mexicana amazonensis. Immunoprecipitation of LCM with an antibody specific for murine granulocyte‐macrophage colony stimulating factor (GM‐CSF) abrogates both activities, indicating that the leishmanial growth‐promoting activity is due to the presence of GM‐CSF on LCM. Furthermore, recombinant GM‐CSF (rGM‐CSF) added to the culture medium or to the immunoprecipitated LCM is able to respectively induce or to partially recover the growth‐promoting activity of the LCM. Sequential in vitro passages of the parasite induces a progressive loss of sensitivity to the growth‐factor. Parasite forms recently collected from lesions are significantly more responsive to the growth‐factor than forms already adapted to grow in culture. Since it has been shown that several different microorganisms display receptors for vertebrate‐like hormones and that GM‐CSF is able to enhance a cutaneous leishmanial lesion, our results permit us to raise the hypothesis that a direct interaction between a host‐derived hormone and a pathogenic microorganism can be of importance in defining the fate of an infection. The fact that GM‐CSF is produced by cells that actively participate in a leishmanial infection (T‐lymphocytes and macrophages) reinforces our hypothesis. Copyright © 1990, Wiley Blackwell. All rights reserved