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Neutrophil lactoferrin release induced by IgA immune complexes differed from that induced by cross‐linking of Fcα receptors (FcαR) with a monoclonal antibody, MIP8a

The human IgA Fc receptor (FcαR, CD89) plays an important role in host defence against invading pathogens. To study the properties of the receptor, 12 MoAbs, namely, MIP7c, MIP8a, MIP9a, MIP10c, MIP11c, MIP14b, MIP15b, MIP38c, MIP59c, MIP65c, MIP68b and MIP71a, were generated. The inhibitory effects of the antibodies on FcαR functions were tested. Three of the antibodies, MIP7c, MIP8a and MIP59c, were able to block up to 90% of soluble FcαR binding to IgA‐coated beads and 70–80% of neutrophil phagocytosis of IgA immune complexes (IC). MIP8a could also inhibit IgA IC‐induced neutrophil lactoferrin release, while cross‐linking of FcαR with MIP8a and anti‐mouse IgG could elicit neutrophil lactoferrin release. However, IgA IC‐induced lactoferrin release required both extracellular calcium and magnesium, whereas MIP8a‐induced release did not require extracellular magnesium and only partially required extracellular calcium. In addition, the time course of IgA IC‐induced lactoferrin release was slow. Lactoferrin was not detectable if the incubation time was less than 0·5 h. In contrast, MIP8a‐induced lactoferrin release was fast. Lactoferrin could be detected within 5 min of incubation. Therefore, neutrophil lactoferrin release induced by IgA IC differed from that induced by cross‐linking of FcαR with MIP8a.