Surface proteins of the human eosinophil. I. Isolation of eosinophil IgG binding proteins.

Proteins involved in the attachment of eosinophils to immobilized antigen-antibody complexes were isolated. Eosinophils, purified from normal human peripheral blood, were surface labelled with 125I-iodide in the presence of lactoperoxidase and hydrogen peroxide. Immobilized immune complexes were prepared by covalent coupling of tetanus toxoid antigen to cellulose and treatment of the fixed antigen with human anti-tetanus IgG. Intact cells were allowed to interact with the antigen-antibody complex and the cells were then lysed in situ with a salt solution containing the non-ionic detergent NP40. After exhaustive washing to remove unattached proteins, the bound proteins were eluted with a buffer containing mercaptoethanol with or without SDS. A major protein of mol. wt 16K and a minor protein of mol. wt 18K were isolated. These proteins were unaffected by the temperature of attachment of eosinophils to the fixed IgG antigen complexes or by the presence of protease inhibitors and did not therefore appear to be proteolytic cleavage products.