In spite of the considerable experimental evidence that Leydig cells maintain the elevated number of macrophages in the testis, the mechanism involved remains to be established. It may involve direct contact via Leydig cell-mac-rophage specializations, although the relatively slow decline in macrophage numbers following Leydig cell destruction by EDS treatment suggests that simple physical attachment is not the mechanism responsible. Other cytokines may be involved; for example, both colony-stimulating factor-1 (CSF-1) and interleukin-1a (IL-1) have been implicated in regulating testicular macrophage function. Normal resident macrophage development in many tissues including the testis is dependent upon CSF-1, while IL-1 is a key mediator of the inflammatory response including monocyte recruitment. buy antibiotics online
However, CSF-1 expression in the adult testis appears to be extremely low, and the role of this cytokine in stimulating testicular macrophage development appears to be exerted systemi-cally, possibly at the level of bloodborne tissue macrophage precursors. Moreover, the principal site of IL-1 production in the testis in the absence of an inflammatory stimulus is the Sertoli cells and spermatogenic cells, rather than the Leydig cells. These data point to the involvement of another, as yet unidentified, Leydig cell cytokine or product.