Enhanced uptake of liposomes by bovine macrophages after opsonization with antibodies to Brucella abortus.

Phosphatidylcholine:cholesterol liposomes containing 4(5) carboxyfluorescein were modified by incorporation of Brucella abortus lipopolysaccharide. These vesicles were opsonized with bovine anti-B abortus or anti-B abortus plus complement. The fluorescent marker entrapped in antibody-opsonized liposomes was taken up by cultured bovine macrophages more effectively than was the same compound which had been loaded into nonopsonized liposomes. The addition of bovine complement to antibody-opsonized liposomes did not increase the extent of 4(5) carboxyfluorescein uptake over that caused by antibodies alone. The system, described in this report, could be used as a model for evaluation of the efficacy of selectively directing liposomes containing antibiotics to macrophages infected with intracellular B abortus, since macrophages possess Fc receptors capable of binding antibody-opsonized liposomes.