CANINE MONOCYTES EXPRESS A RECEPTOR SPECIFIC FOR MURINE FC-GAMMA-2A AND FC-GAMMA-3 IMMUNOGLOBULINS

Murine monoclonal antibodies (mAb) of IgM and IgG subclasses that do not bind to canine cells have been used to detect the expression of Fc receptors on canine peripheral blood mononuclear cells and the cell line MAXEY-DH82. Murine Ig of IgG2a and IgG3 isotypes bound specifically to canine peripheral blood monocytes and to MAXEY-DH82, whereas Ig of IgG1, IgG2b, and IgM did not. No other cell types, including resting and activated peripheral blood lymphocytes, expressed this canine Fc receptor (cFcR) specific for murine IgG2a and IgG3. MAXEY-DH82 was used to characterize this Fcgamma2a/gamma3 receptor. Binding of murine IgG2a and IgG3 is trypsin sensitive and partially suppressed by phosphatidyl inositol-phospholipase C (PI-PLC) treatment, indicating that this cFcgamma2a/gamma3 receptor is a lipid-anchored protein. Preincubation of MAXEY-DH82 with canine sera or canine IgG prevented the binding of murine gamma2a/gamma3 Ig, demonstrating that this receptor is a cFc receptor for canine IgG. The cFcgammaR expressed on canine monocytes and on MAXEY-DH82 is probably the analog of the murine and human FcgammaRI. The specific expression of this analog by canine cells could be used in identifying and purifying canine monocytes.