- Problem This study examined the effect of lipopolysaccharide (LPS) on the capacity of Leydig cells to produce and express interleukin-18 (IL-18), IL-18 receptor (IL-18R) and the IL-1β-converting enzyme (ICE) (IL-18 family), under in vitro conditions. Method of study Primary Leydig cells (LCs) were isolated from murine testis by the Percoll technique, and cultured both in the presence and absence of LPS (0.1, 1, 5 μg/mL) for 3 and 24 hr. LCs were examined for their capacity to produce and express IL-18 family molecules by using immunohistochemical staining (IHC), enzyme-linked immunosorbent assay (ELISA), Western blot and real-time polymerase chain reaction (PCR) analysis. Results Leydig cells were shown to constitutively express IL-18, as examined by IHC, ELISA, Western blot and real-time PCR analysis. Addition of LPS to LC cultures was shown to significantly increase the basal levels of IL-18, in a dose- and time course-dependent manner, as examined by ELISA, Western blot and real-time PCR analysis. In addition, LPS increased LC cultures to express ICE and IL-18 R, as examined by real-time PCR analysis. Conclusion Our results demonstrate that LPS increased the capacity of murine LCs to produce the IL-18 family molecules. IL-18, in the testis, might be involved in the regulation of physiological and infection/inflammatory processes, and thus, could be a component of the autocrine/paracrine factor net that controls steroidogenesis and male fertility; further studies are needed to confirm this possibility.