Role of filter-bound IgA in inhibiting polymorphonuclear leukocyte chemotaxis.

The effects of human serum IgA on human polymorphonuclear leukocyte (PMN) function were studied. In Boyden chambers, chemotactic migration against semipurified C5a as well as the formylated tripeptide FMLP was inhibited in the presence of IgA. Under such conditions, the release of superoxide anion was not changed. In addition, chemotaxis "under agarose" using the leading front evaluation remained unaltered in the presence of IgA despite IgA-induced aggregation of PMN and reduced density of migrating cells. Chemotaxis filters incubated with radiolabelled IgA demonstrated strong binding of IgA, and further, these IgA-pretreated filters impeded PMN migration. Incubation of PMN with IgA followed by subsequent washings did not affect chemotactic migration. These data show that filter binding of IgA is responsible for the inhibition of chemotactic PMN-migration in the Boyden chambers, most probably mediated by increased cell-substrate adhesion. Experiments using casein showed displacement of IgA by casein which enables PMN to fully respond to casein.