The down-regulation of Fc gamma RII and Fc gamma RIIIB by N-formyl-methionyl-leucyl-phenylalanine (FMLP) depends on secretory events in human neutrophils

We have previously demonstrated that N-formyl-methionyl-leucyl-phenylalanin e (FMLP) induces down-regulation of Fc gamma Rs on human neutrophils (PMN) modifying different Fc gamma R-dependent functions. The aim of this work wa s to assess the cellular mechanisms by which FMLP exerts this effect on Fc gamma Rs. The role of the microfilament and cytoskeletal apparatus in this process was evaluated using cytochalasin B (CB), an inhibitor of microfilam ent functions. The expression of Fc gamma RIIIB and Fc gamma RII after CB FMLP treatment was drastically diminished when compared to FMLP-treated ce lls. Neutrophil degranulation induced by FMLP affect only 22% of the cells in response to FMLP. However, the Fc gamma Rs of the whole PMN population w ere reduced, suggesting that secretory products could be responsible for th e down-regulation induced by FMLP or FMLP + CB. In fact, supernatants from FMLP-treated PMN also induced Fc gamma Rs down-regulation on naive neutroph ils. Moreover, supernatants from FMLP + CB-treated PMNs exerted a higher ef fect. Data obtained from permeabilized PMN show that after FMLP treatment t here is an intracellular depletion of both Fc gamma RIIIB and Fc gamma RII. In addition, the Fc gamma R down-regulation is abrogated by phenyl methyl sulfonyl fluoride (PMSF) but not by other protease inhibitors such as pepst atin, thiorphan, phosphoramidon and leupeptin, suggesting a role for serine protease(s) in this process. (C) 1999 Elsevier Science B.V. All rights res erved.