RESUMEN
Non-specific immunostimulants such as plant extracts and natural and synthetic thymic preparations are widely used for enhancing the reactivity of the human defence system in chronic infections, immunodeficiency, autoimmunity and neoplastic diseases. Considering the high prevalence of latent infections by Lymphotropic herpesviruses and their frequent spontaneous reactivation, one wonders whether the stimulation of lymphoid cells by such immunostimulants may further support virus reactivation. We have performed tissue culture experiments using the well defined infectious system of human herpesvirus-6 (HHV-6) and the immature T cell HSB2 to test the effects of echinacin, isoprinosine and thymus factors on the frequency and extent of virus antigen expression in infected cells. The results show that various viral antigens related to virus replication and to the synthesis of structural components appear earlier in cells stimulated with such substances as echinacin, timunox and TP-1, but not following the stimulation with isoprinosine. Similarly, virus genome containing cells as determined by in situ hybridization techniques increased after stimulation with thymic preparations (thymostimulin and thymopentin), but not with echinacin and isoprinosine. The data suggest that the synthesis of proteins or DNA of lymphotropic viruses may be transiently enhanced when lymphoid cells are stimulated by certain non-specific immunostimulants. There was no evidence, however, of increased virus replication. Since the data presented here are rather preliminary results from tissue culture studies, the use of such substances in patients should include a critical monitoring of the activity of lymphotropic viruses to exclude untoward effects through persistent viral activity and/or autoimmune dysregulations (e.g. secondary to selective expression of viral antigens). More detailed studies are needed to this effect including long-term controls in patients treated by these substances.