The objective of this research program is to define the cytokines elaborated by monocytes and the molecular mechanisms that regulate their expression. Exposure to TGF-beta influences the responsiveness of monocytes to secondary stimuli such as lipopolysaccharide (LPS). Pretreatment with TGF-beta results in a dramatic increase in the level of LPS-induced GM-CSF RNA and protein. However, similar treatment results in a 50% reduction in the level of IL-1 and TNF-alpha RNA. While LPS alone induces the expression of a variety of monokines, pretreatment with TGF-beta appears to prime the cells to the effects of LPS, influencing not only the magnitude of the response but also the kinetics. This interplay between inflammatory cells and cytokines may be important in the regulation of the immune response. Moreover, modulation of cytokine expression may influence the outcome of diseases such as AIDS. Exposure of monocytes to HIV-1, the etiological agent of AIDS, results in a biphasic induction pattern of cytokine expression, most notably TNF-alpha. The close association of HIV-1 and monocyte gene expression suggests that they may share a common regulatory mechanism. HIV-1 gene expression in transfected THP-1 cells (a mature monocyte cell line) is increased after stimulation with LPS, suggesting that cytokine induction may influence viral expression. However, cotransfection of the TNF-alpha promoter with TAT, a transactivator protein for HIV-1, does not lead to increased TNF expression. Analysis of nuclear proteins demonstrated that resting monocytes constitutively express NF-(kappa)B binding proteins and the level of expression is relatively unchanged by the state of activation or by infection with HIV-1. However, preliminary studies suggest that a TNF-binding protein is upregulated in HIV-1-infected monocytes and may be important in the induction of TNF gene expression.
