Effects of human intravenous immunoglobulin on canine monocytes and lymphocytes

Objective-To evaluate interactions of human intravenous immunoglobulin (IVI G) with canine lymphocytes and monocytes. Sample Population-Heparinized blood samples from 4 clinically normal Beagle s. Procedure-Binding ability of IVIG to canine lymphocytes and monocytes was m easured by flow cytometry and an indirect immunofluorescent assay. Dual-sta ining fluorescent assays were done to determine lymphocyte subsets that bin d IVIG. Competitive assays were done, using intact canine IgG and Fc fragme nts, and inhibition of binding was compared with that of F(ab)(2) fragments . Ability of IVIG to inhibit phagocytosis of antibody-coated canine RBC als o was determined, using a canine mononuclear cell phagocytic assay. Results-IVIG concentrations (10, 1, 0.1, and 0.01 mg/ml) bound to (mean +/- SD) 99.6 +/- 0.4, 92.4 +/- 6.1, 20.4 +/- 24.6 and 2.0 +/- 5.1% of canine l ymphocytes, respectively, Dual staining analyses with IVIG and canine lymph ocyte markers indicated that IVIG bound to CD4, CD8, and B lymphocytes, The aforementioned 4 IVIG concentrations bound to 98.0 +/- 2.1, 85.5 +/- 13.5, 64.7 +/- 32.8, and 26.5 +/- 17.1% of monocytes, respectively. Inhibition o f IVIG (0.01 mg/ml) binding to monocytes was significant(P < 0.05) in the p resence of 1 and 10 mg of canine IgG/ml and 1 mg of canine Fc fragments/ml. In the presence of F(ab')(2) fragments of canine IgG, inhibition was not s ignificant, suggesting that binding is Fc mediated. Go-culturing of monocyt es, opsonized RBC, and the 4 concentrations of IVIG and no IVIG resulted in 11.8 +/- 5.1, 27.7 +/- 12.3, 31.8 +/- 15.1, 53.8 +/- 6.7, and 45 +/- 12% o f the monocytes containing RBC, respectively. Phagocytosis inhibition was s ignificant (P < 0.05) at an IVIG concentration of 10 mg/ml, Conclusions-IVIG binds to canine lymphocytes and monocytes; binding to the latter is Fe mediated. IVIG also inhibits Fc-mediated phagocytosis of antib ody-coated RBC. Clinical Relevance-Owing to its ability to inhibit Fc-mediated phagocytosis of antibody-coated RBC, IVIG may be an effective short-term treatment for dogs with immune-mediated hemolytic anemia.