Phospholipase A2 activity of Fc gamma 2b receptors of thioglycollate-elicited murine peritoneal macrophages.

The detergent lysate of plastic adherent cell population of thioglycollate-elicited peritoneal exudate cells from 100 individual Swiss mice was subjected to affinity chromatography on two different media, Sepharose coupled to heat-aggregated human IgG (IgG-Sepharose) and Sepharose coupled to the phosphatidylcholine analog, rac-1-(9-carboxyl)nonyl-2-hexadecylglycero-3 -phosphorylcholine (PC-Sepharose). Both IgG- and PC-binding proteins were further purified by Sephadex G-100 gel filtration and isoelectric focusing in the presence of 6M urea. Both IgG- and PC-binding proteins thus purified appear to be homogeneous in size as well as charge properties. The IgG-binding proteins of a molecular weight of 25,000 had an isoelectric point of 4.8, whereas the PC-binding proteins of a molecular weight of 42,000 were more basic and had an isoelectric point of 6.0. Both materials retained their IgG-binding capabilities as judged by their inhibitory capacity of murine EA gamma rosetting systems. The subclass specificities of the IgG- and the PC-binding proteins were for IgG2a and IgG2b, respectively. The PC-binding proteins possessed a typical phospholipase A2 activity, which was maximal at pH 9.5, depended on Ca++, and was specific for cleavage of fatty acid from the sn-2 position of phosphatidylcholine. The binding of aggregated IgG2b to the PC-binding proteins caused the ninefold increase in noted enzymatic activity in the presence of, but not in the absence of, Ca++ (5mM). The IgG-binding proteins on the other hand, lacked any detectable phospholipase A2 activity. Thus, the biochemical and biological properties of the PC- and IgG-binding proteins isolated from murine peritoneal macrophages are essentially identical to those homologous proteins previously isolated from P388D1 cells [20].