Cytokines elaborated by and affecting peripheral blood monocytes are pivotal mediators in controlling inflammation. The focus of this laboratory is on understanding the regulatory events and mechanisms which control the inflammatory response, specifically: 1) elucidating cytokine signal tranduction pathways whcih, if inhibitied, can alter cytokine effects, 2) examining programmed cell death (PCD) as a means by which the number of cells at an inflammatory site is controlled. With regard to the first focus, our studies have showed that human monocytes express only the type II receptor for tumor necrosis factor- alpha (TNF-alpha), (2000 receptors/cell, KD=230 pM). Although this receptor has been shown not to contain any intrinsic kinase activity in its intracellular domain, our signal transduction studies showed the TNFalpha receptor/ligand interaction indirectly triggers tyrosine kinase activity/resulting in greatly enhanced tyrosine phosphorylation of a 43 kD protein. Inhibition of this tyrosine kinase activity eliminated the TNFalpha-stimulated functions of reactive oxygen intermediate generation and inflammatory cytokine mRNA production. Additional studies have identified a pivotal role for specific phosphatases as an off-signal for cytokine-triggered cytokine production. Inhibition of these enzymes greatly increases the magnitude and duration of cytokine synthesis triggered by inflammatory stimuli. Prolonged cytokine synthesis may further regulate inflammatory cell accumulation and activation by preventing activation of an endogenous endonuclease responsible for PCD.
