[Protective effect of a human immunoglobulin preparation on mouse experimental infection of methicillin resistant...

Methicillin resistant Staphylococcus aureus (MRSA) selectively increased by extensive chemotherapy is now one of the major causative agents of opportunistic infections in immunocompromised patients. Immunotherapy should be applied because this infection is based on the immunocompromised state of the patients. But this therapy has not been applied because S. aureus is known to have protein A which binds to the Fc portion of IgG and blocks phagocytosis through Fc receptor of phagocytic cells which plays the major role for the killing of infected bacteria in vivo. It should be known that MRSA strains often did not express protein A. Recently isolated MRSA strains were collected from three medical institutions and examined for their expression of protein A. Incidences of protein A-negative strains were different among institutions. It was found that more than a half of the strains from a general hospital which expressed typical heat sensitive methicillin resistance did not express protein A, but that incidences of protein A-negative strains were around 20% in the MRSA strains of a complicated history from a university hospital and a research center. All protein A-negative strains were found to be agglutinated by a commercially available immunoglobulin preparation (Venilon). And this immunoglobulin was proved to have a protective effect for the mouse experimental infections of these protein A-negative MRSA strains.