The role of the TLR-dependent signaling pathway in the mechanism of phagocyte protection by exogenous heat shock protein HSP70 from the endotoxin action

305 Endotoxins play an important role in the developp ment of a Grammnegative sepsis, as well as in some diss eases, such as metabolic syndrome and coronary heart disease [1]. The effect of endotoxins (lipopolysacchaa rides, LPS) on the target cells is realized via Tollllike receptors 4 (TLR4) which they contain. Entering the bloodstream, LPS first interact with the LPSSbinding protein and then with CD14 receptors of the target cells (including blood phagocytes). Then, LPS pass from CD14 to MDD2 (lymphocyte antigen 96) with subsequent formation of two LPS–MDD2–TLR4 complexes, which further form a heterodimeric comm plex in the target cell membrane [2]. Signal transducc tion from this complex activates transcription factors (in particular, NFFκB, nuclear factor kappa B) and triggers the cell response, characteristic of which is an increase in adhesion factors and synthesis of proinn flammatory cytokines, TNFFα being the first to be synthesized [3]. In inflammatory diseases (in particular, sepsis), the synthesis and secretion of heat shock proteins (HSP70) are elevated, which plays an important role in the mechanism providing protection from heat shock and other types of stress. It is assumed that HSP70 can bind to TLRs [4]. Application of exogee nous recombinant HSP70 decreases the animal morr tality rate in the septic shock model, as well as inhibits endotoxinninduced activation of neutrophils and macrophages [5]. Study of the effects of HSP70 and LPS on TLR expression has yielded ambiguous results, suggesting both an increase and a decrease in TLR expression induced by HSP70 and LPS [6, 7]. The effect of intraa cellular HSP70 has been rather comprehensively studd ied; however, the mechanisms underlying the action of extracellular HSP70 are still unclear. We have studied the role of the TLRRdependent signaling pathway in the mechanism underlying the protection of blood phagocytes from endotoxins by the exogenous heat shock protein HSP70. We have earlier demonstrated that exogenous HSP70 protects innate immunity cells from endotoxins [5]; however, the mechanism of its protective action is unclear. Here, we have shown that HSP70 increases the numm ber of TLR2 and TLR4 on the cell membrane of neuu trophils and monocytes and insignificantly elevates TNFFα production by these cells predominantly with involvement of TLR44dependent signal transduction. On the other hand, exogenous HSP70 decreases the LPSSinduced increase in TLR2 and TLR4 expression in these cells. MATERIALS AND METHODS The following reagents were used in this study: E. The gene of recombinant human …