Role of cell surface contact in the kinetics of superoxide production by granulocytes.

Abstract

A C T The complement-derived anaphylatoxin C5a and a putative analogue of bacterial chemotactic factor (N-formyl-methionyl-leucyl-phenylalanyl [fMLP]), as well as bacterial lipid A, all stimulate human granulocyte (PMN) adhesiveness and superoxide (O) production in a concentration-dependent manner. Since attachment of particulate matter to the PMN membrane is an early event in the triggering of respiratory burst of these cells, we further examined how adherence might modulate the release of 2 induced by soluble mediators of inflammation. We found that both the quantity and kinetics of 2 production depend on prior attachment of the cells to a surface. In stirred suspensions of PMN, fMLP induces only a short burst (2.5 min) of 2 release associated with reversible PMN aggregation. The magnitude, but not the time course, of both these responses depend on the fMLP concentration. Unlike the short respiratory re- sponse of cells in suspension, PMN allowed to settle onto stationary petri dishes, then overlaid with fMLP, rapidly spread and attach to the surface where they remain and release 2 throughout the 60-mi test pe- riod. Prolonged 2 release also follows fMLP stimu- lation in suspensions of PMN pretreated with cyto- chalasin B, in which case aggregation becomes irreversible during the 20-min burst. If fMLP is slowly infused into a suspension of cells at 37C or if PMN are challenged at 0C, and then warmed to 37C, 2 release greatly decreases or becomes undetectable. Suspended PMN do not respond to a second challenge by the same stimulus regardless of the rate or tem- perature at which the first stimulus was added, a phenomenon formerly described as desensitization. How- ever, if PMN challenged with fMLP in suspension un- dergo the short respiratory response and then are later placed in petri dishes, they adhere and resume pro-