Protective Effect and Antibody Titer of Intravenous Immunoglobulin (IVIG) against Clinical Isolates of Opportunistic Bacteria

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Abstract
Neonates and leukopenic, immunosuppressed 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 102,400. 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 400,000 to 12,800,000, 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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