Neonates and leukopenic, immunosupressed patients are at high risk for severe infection of opportunistic pathogens despite of the availability of potent antimicrobial agents. In this study, antibody titers of immunoglobulin preparations (IVIG) were contrasted with the protective effect in mice against each of bacterial infection. Antibody titers were determined by ELISA. The antigens were 70-80 clinical isolates of Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae and Staphylococcus aureus, respectively. Antibody titers of IVIG against these three gram-negative bacteria ranged 3200 to 102400. ICR mice were inoculated intraperitoneally with each of several strains against which IVIG showed various titers. IVIG showed rather high protective activities against well-reactive strains, while it showed little protective activities against poor-reactive strains. In the case of P. aeruginosa, statistical analysis of the results obtained with the antibody titer and efficacy showed a good correlation (p<0.01). On the other hand, IVIG showed a high and complicate antibody titer against S. aureus IVIG ranging 400000 to 12800000, since apparent titers contained non-specific binding of Fc portion of IgG with protein A on the cell wall. IVIG was active in mice, where protein A was less and specific binding was stronger. Bacterial cells have various components ; lipopolysaccharide, lipid A, capsule, flagella, pill, etc. that are responsive to specific antibodies. This study indicates that IVIG have such antibodies and that is associated with protective activity against bacterial infection in proportion to antibody titer.

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Keeping the pH constant during the incubation of sample and complement solutions was an inportant factor to obtain a reproducibla ACA value. Lyophilized complement shows a pH of 8.8-9.0 after reconstitution. The pH of frozen complement is 7.2-7.4. When the ACA of an intravenous IgG (IVIG) was tested with the reconstituted complement, the ACA value was higher than when the preparation was tested with frozen complement.
Ionic strength also affected the ACA test of an IVIG which did not contain ionic substances such as NaCl or glycine. Even when the pH and ionic strength of commercial IVIG preparations were standardized by dialysis, the concentration of IgG polymer did not necessarily correlate with the ACA value.

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