Estimation of the degree of opsonization of homologous erythrocytes by IgG for intravenous and intramuscular use.

In an effort to evaluate the capacity of polyspecific IgG preparations to sensitize homologous erythrocytes, immunoglobulin G for intramuscular use and an IgG preparation for intravenous use were tested for their tendency to associate with and to opsonize homologous erythrocytes. It was found that the amount of IgG associated with erythrocytes by far exceeded the opsonic moiety. Erythrocytes incubated in IgG in amounts higher than that achieved in vivo after 5 infusions of 0.4 g/kg body weight each, were sometimes lightly opsonized when tested on rosette formation with and phagocytosis by adherent monocytes. IgG for intravenous use was lower than IgG for intramuscular use in its opsonic activity and did often not reach the level of significance. Comparison with rosette formation and phagocytosis of erythrocytes with known amounts of antibodies allowed the prediction that following high-dose infusion of IgG, less than 25 opsonic molecules per red blood cell are achieved in recipients of blood groups A, B, and AB (and probably even less in those of blood group (O). Erythrocytes preincubated in polyspecific IgG failed to inhibit phagocytosis of optimally sensitized erythrocytes by cultured macrophages.