Differences in intracellular pool and receptor-dependent mobilization of the adhesion-promoting glycoprotein Mac-1...

Recruitment of cells to an inflammatory site is a process that is selectively regulated. At an inflammatory site caused by bacterial infection, predominantly neutrophil accumulation is observed. This is in contrast to allergic inflammation, where predominantly eosinophil accumulation occurs. Mac-1 is an inducible adhesion molecule for both neutrophils and eosinophils. We examined the mobilization of this receptor on neutrophils and eosinophils after exposure to factors related to bacterial infections and allergic inflammation. We found more pronounced mobilization of Mac-1 on neutrophils than eosinophils after exposure to N-formylmethionyl-leucyl-phenylalanine, lipopolysaccharides, and activated sera (C5a). There was no significant difference in Mac-1 expression after exposure to aggregated immunoglobulin G. Incubation with interleukin-5 (IL-5) caused a significant increase of Mac-1 expression on eosinophils but not on neutrophils. Neutrophils seem to respond to a greater extent than eosinophils to factors related to bacterial infections, whereas eosinophils respond better to IL-5 associated with allergic inflammation. We measured the total pool of Mac-1 to evaluate whether these differences could depend on the size of the intracellular pool. Eosinophils had a larger total pool of Mac-1 than neutrophils. This finding increases the difference between eosinophils and neutrophils when relating the mobilized pool to the total pool. Stimulation with receptor-independent stimuli such as phorbol myristate acetate and ionomycin induced more pronounced mobilization of Mac-1 on eosinophils, but no differences were obtained if the mobilized pool was related to their total pool. These results indicate that the difference in responsiveness depends on different receptor-mediated signaling, since receptor-independent stimulation resulted in relatively similar mobilization of the intracellular pool of Mac-1.