TGF-beta in infections and infectious diseases.

Since it was first described as having the ability to inhibit macrophage activation, transforming growth factor-beta (TGF-beta) has been analyzed for its role in regulating immune responses to a variety of pathogens, including viruses, bacteria, yeast, and protozoa. Most of the studies have involved organisms that infect macrophages, and this discussion will attempt to highlight these findings. Perhaps the most work has been performed with protozoan pathogens, including Trypanosoma cruzi and a variety of Leishmania species, so the discussion will begin with these organisms. Other studies have focused on mycobacteria and viruses, including human immunodeficiency virus, so these areas will also be emphasized in the discussion. For the most part, investigators have reported that TGF-beta has, as expected, a negative influence on host responses and a beneficial effect on the survival and growth of intracellular pathogens. However, other studies have found that TGF-beta may have a positive or beneficial effect in some models of infection. This review will attempt to highlight studies and conclusions on the roles of TGF-beta in infection.