Opsonins as Determinants of Survival in Intraperitoneal Infections of Mice

Abstract

IT has recently been established that the rapidity with which various species of Gram-negative organisms are eliminated from the mouse peritoneum, is entirely dependent on the availability of opsonic factors^1,2. In the normal mouse peritoneum there are large numbers of mononuclear cells³ which, once they have engulfed the injected bacteria, destroy them equally rapidly irrespective of their virulence for the mouse. The limiting factor which determines whether overall bacterial multiplication occurs is the rate at which the organisms are phagocytosed, and this is controlled by the supply of opsonic factors. Virulent strains for example of Salmonella typhimurium require greater concentrations of serum opsonic factors to promote phagocytosis than do avirulent members of the same species⁴. That these considerations apply to intraperitoneal infections was apparent by the finding that pretreatment of virulent S. typhimurium organisms with dilute specific antiserum before injection, greatly altered the capacity of these organisms to cause disease and death in mice¹. Treatment by dilute antiserum did not by itself affect the viability of the organisms. It seems clear that the trace amounts of antiserum adsorbed by the injected bacteria rendered them susceptible to phagocytosis and this changed the whole balance of the host/parasite interaction.