PHAGOCYTOSIS OF PSEUDOMONAS-AERUGINOSA FAILS TO ELICIT HEAT-SHOCK PROTEIN EXPRESSION IN HUMAN MONOCYTES

Phagocytosis represents, a powerful stress for the phagocytic cells. P hagocytosis of Staphylococcus aureus induces a stress response associa ted with the synthesis of specific heat shock/stress proteins (HSP). H ere we investigated the stress response of human monocyte-macrophages (m phi) to Pseudomonas aeruginosa, a bacterium found, as for S. aureus , in the airways of patients suffering cystic fibrosis. P. aeruginosa activated in m phi the production of both extra- and intracellular O-2 (-) increased Interleukin-1 beta and actin, but failed to induce host HSP. Neither S. aureus exotoxins nor the scavenging property of P. aer uginosa's alginate, but the lower toxicity of P. aeruginosa and/or dif ferential activation of proteine kinase C (PKC) by the two bacteria, m ight explain their differences in host HSP induction. While O-2(-) is insufficient to induce HSP synthesis in m phi, hydroxyl radicals, gene rated in the presence of exogenous iron, is a likely additional signal , along with PKC activation, for HSP induction during bacterial phagoc ytosis.