MACROPHAGE-MIGRATION INHIBITORY FACTOR PRODUCTION BY LEYDIG-CELLS - EVIDENCE FOR A ROLE IN THE REGULATION OF TESTICULAR FUNCTION

Macrophage migration inhibitory factor (MIF), described originally as a product of activated T lymphocytes, recently has been found to be re leased by monocytes/macrophages and the anterior pituitary gland. Immu nohistochemical studies of the adult rat testis using an affinity-puri fied polyclonal antimurine MIF antibody demonstrated strong staining f or MIF in Leydig cells and their putative precursors. Peritubular myoi d cells and the seminiferous epithelium were negative for MIF staining ; however, a weak reaction around the heads of elongated spermatids al so was observed. The expression of MIF messenger RNA and protein in wh ole rat testis was demonstrated by Northern blot and Western blot anal yses, respectively. Both MIF messenger RNA and protein immunoreactivit y in Leydig cells was observed in testes obtained from long term hypop hysectomized rats. Significant concentrations of intracellular MIF wer e detected in lysates of the TM3 Leydig cell line (7.23 +/- 2.6 pg/mu g protein), and testicular interstitial fluid contained 14.7 +/- 1.6 n g/ml MIF protein, as measured by MIF-specific enzyme-linked immunosorb ent assay. To gain insight into the possible biological role of MIF in the testis, cultures of adult rat seminiferous tubules and purified L eydig cells were incubated together with recombinant murine MIF (rMIF) . Neither rMIF (50 ng/ml) nor a neutralizing anti-MIF antiserum was fo und to affect basal or LH-stimulated Leydig cell steroidogenesis in vi tro. However, a dose-dependent decrease in the secretion of inhibin by the seminiferous tubules was observed at rMIF concentrations ranging from 10-100 ng/ml. Taken together, these data indicate that Leydig cel ls produce MIF in vivo and suggest an important regulatory role for th is newly discovered mediator of testicular function.