MODULATION OF THE IMMUNE-RESPONSE BY TRANSFORMING GROWTH-FACTOR-BETA

For the past several years immunologists have been fascinated by a series of experiments showing that transforming growth factor beta (TGFbeta) suppresses T- and B-lymphocyte growth as well as IgM and IgG production by B cells. Moreover, while exerting chemotactic activity on monocytes and inducing expression of interleukin-1 and interleukin-6 by these cells, TGFbeta interferes with bacterially induced tumor necrosis factor alpha production, oxygen radical formation and the adhesiveness of granulocytes to endothelial cells. These mechanisms may provide the basis for the effect of TGFbeta to prevent the microvascular changes associated with brain edema formation in bacterial meningitis. Given the potential of lymphocytes as well as macrophages to produce TGFbeta1, this cytokine may exert negative feedback signals on the immune response, provided the cytokine is processed from its latent form to the bioactive homodimer. Potent effects of TGFbeta have been observed in experimental animals including the inhibition of the generation of virus-specific cytotoxic T cells and antiviral antibodies as well as the diminution of cellular infiltrates with decreased major histocompatibility complex class-II expression and CD8+ T cells in the tissue of virally infected animals. TGFbeta may also be of importance in tumor immunology. By the production of bioactive TGFbeta as detected in glioblastoma and acute T-cell leukemia, tumor cells may induce an immunodeficiency state and escape immune surveillance. In inflammation, monitoring of TGFbeta in the tissue will bring light on the immune regulation in acute and chronic inflammatory diseases.