Effect of Salmonella typhimurium G 30 on macrophages in the protection against mouse typhoid

Abstract

The work reported in this thesis has been undertaken to investigate some of the factors which protect a host against those microbial intracellular parasites, which are able to penetrate the intestinal epithelium, such as Salmonella typhi. We have used "mouse typhoid" as our model. The work is aimed to determine the effect of oral immunization by the avirulent G 30 strain of S. typhimurium C 5 in protection against "mouse typhoid". In particular, it has looked at the proliferation of macrophages in the Peyer's patches (PP), an important component of the gut associated lymphatic tissue (GALT) following oral immunization of BALB/cJ mice with G 30 and the ability of these cells to kill ingested S. typhimurium C 5. Mouse protection tests were performed concomitantly to demonstrate the protective capacity of the orally administered G 30. The results show that oral feeding of G 30 not only increased the numbers of Peyer's patch macrophages, far above the normal level, but that then index of intracellular killing was also raised, most significantly. Both of these phenomina correlated with the observed protective effects of G 30. Further, the macrophages were shown to be activated well above the normal threshold, by esterase staining and increased ingestion of latex particles. The in vitro intracellular killing assay showed an absolute requirement for specific antibody against the target parasite, not only for opsonization but also for the subsequent intracellular killing. These finding indicate that oral feeding of G 30 to BALB/cJ mice can generate a good protection against "mouse typhoid". This appears due to an increase in the number of PP macrophages and an increase in the intracellular killing of the pathogen in the presence of specific antibody. In summary, we find a stimulation of a local antibacterial cell mediated immunity in mice to mouse typhoid, following the oral administration of the avirulent G 30 strain.