REGULATION OF CD18 EXPRESSION IN HUMAN NEUTROPHILS AS RELATED TO SHAPE CHANGES

The study analyses the distribution and quantitative expression of sur face CD18 of neutrophils exposed to distinct stimuli that produce diff erent types of continuous shape changes, including types that are asso ciated with locomotion and others that are not. The chemotactic peptid e N-formyl-L-norleucyl-L-leucyl-L-phenylalanine, colchicine and nocoda zole were used to induce a polarized locomotor morphology, phorbol myr istate acetate, 1,2-dioctanoylglycerol and 1-oleoyl-2-acetylglycerol t o induce non-polar motile cells ruffling all over the surface and (H2O )-H-2 to induce non-polar cells performing circus movements as have be en previously described. Except for colchicine and nocodazole, these s timuli increased surface expression of CD18. Thus, stimulated shape ch anges are frequently, though not always, associated with increased sur face expression of CD18. High concentrations (10(-7) to 10(-5) M) of p horbol myristate acetate but not of chemotactic peptide induced down-r egulation of surface CD18. Cytochalasin D (10(-4) M) stimulated CD18 e xpression even though it inhibited shape changes. The surface distribu tion of CD18 determined by light microscopy was uniform in unstimulate d cells or in various forms of stimulation except for cells treated wi th 10(-5) M cytochalasin D. Cytochalasin D (10(-5) M) produced CD18 ac cumulation at the pole opposite the F-actin cap. Experiments with colc hicine, nocodazole, (H2O)-H-2 and cytochalasin D suggest that microtub ules as well as microfilaments modulate surface expression of CD18. Th e results suggest that protein kinase C and phosphatases play a role i n regulating surface expression of CD18 in neutrophils. Increased CD18 expression in response to phorbol myristate acetate, but not in respo nse to chemotactic peptide was inhibited by the protein kinase C inhib itor Ro 31-8220 (10(-6) to 10(-5) M). Ro 31-8220 (10(-5) M) alone incr eased CD18 expression of initially resting cells. Furthermore, the pho sphatase inhibitor okadaic acid (5 muM) and calyculin A (0.04 muM) sup pressed CD18 expression in chemotactic peptide-treated cells, but ther e was no detectable effect in phorbol myristate acetate-stimulated cel ls. This indicates that at least two different pathways mediating CD18 expression are operative in human neutrophils, one being protein kina se C-dependent, the other(s) probably being protein kinase C-independe nt.