IDENTIFICATION OF IL-6 AS ONE OF THE IMPORTANT CYTOKINES RESPONSIBLE FOR THE ABILITY OF MONONUCLEAR-CELLS TO STIMULATE SERTOLI-CELL FUNCTIONS

There is increasing evidence that locally produced cytokines may play an important role in the control of testicular function. In a previous report we demonstrated that medium conditioned by activated human per ipheral blood mononuclear cells (PBMC-CM), which is a rich source of c ytokines, has extremely potent effects on Sertoli cell transferrin and cGMP secretion. Part of this activity could be explained by interleuk in-1 beta (IL-1 beta) but additional cytokines were evidently involved . In the present study we tried to characterize and purify additional components active on Sertoli cells from PBMC-CM. To this end PBMC-CM w as subjected to a purification procedure involving successively: adsor ption to silicic acid, affinity chromatography with an antiserum recog nizing a mixture of cytokines except IL-1 beta, gel-filtration, revers ed-phase HPLC and cation-exchange FPLC. Throughout this protocol a Ser toli cell bioassay was used to monitor the effects on transferrin and cGMP production. After cation-exchange FPLC, SDS-PAGE using silver sta ining showed a single protein band in the bioactive fractions. NH2-ter minal amino-acid sequencing revealed that the active principle(s) in t his band corresponded to four truncated forms of IL-6 missing the firs t 13, 14, 17 and 18 N-terminal amino-acids, respectively. The truncate d IL-6 molecules were as active as intact IL-6 in the Sertoli cell bio assay. Since neither IL-1 beta nor IL-6 alone or in combination could account for the extremely potent effect of PBMC-CM, we tested a series of additional cytokines (IL-1 alpha, TNF-alpha, IL-4, TGF-beta, IFN-g amma) alone and in combination with IL-1 beta and IL-6. These data sug gest that IL-1 beta, IL-6 and TNF-alpha display more than additive eff ects on Sertoli cell transferrin and cGMP secretion and that the combi nation of these cytokines may explain the major part of the effects ob served with crude PBMC-CM. The observation that the latter effects cou ld be observed with murine as well as human IL-1 beta, IL-6 and TNF-al pha further supports the potential physiological relevance of these fi ndings. (C) 1997 Elsevier Science Ireland Ltd.