MUTUAL CONTACT OF ADHERENT POLYMORPHONUCLEAR LEUKOCYTES INHIBITS THEIR GENERATION OF SUPEROXIDE

Superoxide generation by polymorphonuclear leukocytes (PMNs) in suspen sion, or adherent to glass or plastic, after stimulation with N-formyl methionyl-leucyl-phenylalanine or phorbol myristate acetate was measur ed by cytochrome c reduction and spin trapping. Amounts of superoxide generated by adherent PMNs were inversely related to cell density. The generation of hydrogen peroxide was also inhibited at higher cell den sities. In contrast to adherent cells, superoxide released by PMNs in suspension linearly increased with respect to cell number over a wider range. Microscopic observation indicated that the number of cells in mutual contact increased rapidly at cell densities higher than 4 x 10( 4) cells/cm(2), and inhibition of superoxide became apparent at higher cell densities. Mediators which could be released by PMNs, such as NO and adenosine, were not the cause of inhibition. These data suggest t hat mutual contact of PMNs suppresses their generation of superoxide. Survival rates of PMNs after stimulation increased at higher densities , indicating that the mutual contact-induced inhibition of superoxide generation by PMNs may be physiologically relevant at sites of inflamm ation.