Interferons and interferon-induced antiviral proteins in the testis
Introduction
The mammalian testis encompasses two main compartments (a) the interstitium that, in addition to the Leydig cells is responsible for testosterone production contains macrophages, fibroblasts, blood and lymphatic vessels and (b) the seminiferous tubules that are bordered by the peritubular myoid cells and composed of the different generations of germ cells associated with the somatic Sertoli cells (Jégou, 1993).
Surprisingly, the development of sexually transmissible diseases and the increase of the occurrence of testicular cancer had not led to research on the antiviral capabilities of testicular cells, which might be an important reservoir for sexually transmissible or oncogenic viruses. Concerning HIV, some studies have shown that the virus is present in spermatogonia and spermatocytes (Nuovo et al., 1994), as well as in spermatozoa (Baccetti et al., 1994), although there are controversies in this area (Pudney and Anderson, 1991). However, HIV-infected men are often azoospermic or oligospermic (Alexander, 1990) and their testosterone rate is usually diminished at the latest stages of the disease (Villette et al., 1990, Raffi et al., 1991). In this context, we have decided to search for a potential antiviral defense system within the testis, by researching interferons (IFNs) and IFN-induced proteins.
IFNs are small proteins well known for their crucial involvement in the cellular antiviral action. Once produced by the cells, IFNs bind to specific cellular receptors, either on the producing cells themselves or on neighbouring cells, and then induce the expression of several proteins, among which three different gene products, namely 2′5′ oligoadenylate synthetase (2′5′ AS), double-stranded RNA-activated protein kinase (PKR) and Mx protein have attracted much attention due to their ability to generate an antiviral state (Staeheli, 1990, Samuel, 1991).
In order to investigate the testicular antiviral defense system, we have first studied IFNs expression in the seminiferous tubules (Dejucq et al., 1995) and in the interstitium of the rat testis (Dejucq et al., 1997). Then, we have focused on the production of the three main IFN-induced proteins by the cells of the rat seminiferous tubules (Dejucq et al., 1997).
Our results show that antiviral activity is mainly assumed by the testicular somatic cells, both in the seminiferous tubules (peritubular and Sertoli cells) and in the interstitium (macrophages and Leydig cells), while germ cells (spermatogonia, pachytene spermatocytes and early spermatids) appear virtually devoid of a self defence.
Section snippets
Testicular cell cultures
Sertoli cells and peritubular cells were prepared according to a technique previously described (Dejucq et al., 1995). Pachytene spermatocytes and early spermatids were purified by centrifugal elutriation (Pineau et al., 1993). Highly enriched Leydig cells and testicular macrophages were prepared according to the multistep isolation method of Klinefelter et al. (1988). Spermatogonia were obtained using the separation method previously described by Dym et al. (1995).
For IFN search, cells were
mRNA expression: RT-PCR experiments
Using specific primers, we found IFN-α mRNA expression in control Leydig cells, testicular macrophages, Sertoli cells, spermatogonia, spermatocytes and early spermatids, but no expression in control peritubular cells. However, in the latter cells, the IFN-α mRNA was induced after Sendai virus stimulation.
Protein activity: IFN bioassay
Basal antiviral activity was clearly detected in testicular macrophages and, to a much lesser extent, in early spermatids and pachytene spermatocytes. Among all the testicular cells, the best
Discussion
To understand how the testicular antiviral defence system is organised, we investigated IFNs expression within the testis and examined the expression of the three main IFN-induced proteins within the seminiferous tubules. The protection of the germ cells against viruses is indeed of prime importance, as their infection could result in the total destruction of the germ line or generate the diffusion of the virus or viral DNA to all germ cell classes, including the spermatozoa themselves. Among
Acknowledgements
This study was supported by funds from INSERM, Ministère de l’Education Nationale, de la Recherche et de la Technologie, Région Bretagne and Foundation Langlois. N. Dejucq was a recipient of a Conseil Régional de Bretagne fellowship.
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