Non-Specific Immunity in Pneumococcal Infection of Mice

Abstract

THE development of early, non-specific protection against experimental infections with Gram-negative micro-organisms has been observed following injection of bacterial endotoxin, lipopolysaccharide and lipid A¹. Reports of similar activities of these substances against infections with Gram-positive organisms are less numerous and have been substantiated only in the case of infection with Staphylococcus pyogenes or Mycobacterium fortuitum². In an attempt to assess the role of phagocytosis by cells of the liver and spleen in this non-specific protection, we have utilized certain fatty acid esters which are capable of profoundly increasing or reducing the activity of these cells³. One of the experimental models selected for this work has been infection with Streptococcus pneumoniae in mice. Infections with this organism have usually been carried out by the intraperitoneal route and are highly lethal, unless the infection is modified by the classical means of active or passive immunization. In an attempt to demonstrate other, perhaps less potent, protective mechanisms, we felt that a less-virulent type of infection might be more appropriate. This has been achieved by using a strain of Strep. pneumoniae type 8, preparing the challenge inoculum in 0.1 M phosphate buffer at pH 7.4 and injecting the chosen dose of organisms by the intravenous route. Details of this technique will be published fully elsewhere.