Heat-shocked monocytes are resistant to Staphylococcus aureus-induced apoptotic DNA fragmentation due to expression of HSP72

Human peripheral blood monocytes became apoptotic following phagocytosis of Staphylococcus aureus. The consequences of heat stress for monocytes were studied with regard to the effect on S. aureus-induced apoptosis. Exposure of monocytes to 41.5 degrees C for 1 h resulted in RSP72 expression and had no influeuce on phagocytosis of bacteria; moreover, phagocytosis of S. aur eus immediately or shortly after heat shock had no effect on the S. aureus- induced monocyte apoptosis, as evidenced by DNA fragmentation assay. In con trast, cells which recovered from heat shock for 18 to 24 h, although activ e as phagocytes, were resistant to the S. aureus-induced apoptosis. The obs erved protective effect was related to the induction of HSP72, since blocki ng of HSP72 synthesis by an antisense oligomer abolished the protective eff ect of heat shock on bacterium-induced monocyte apoptosis.