Seasonal variations in endotoxin sensitivity.

In the autumn season in rabbits of the same strain we have seen a spontaneous (natural) resistance to either or endotoxin revealed by the Shwartzman reaction model. This `spontaneous' resistance could easily be increased by two small doses of endotoxin, in contrast to January and June. Apart from the difference of the season, the experiments were carried out under identical conditions. The animals, however, were not air-conditioned and the seasonal variation in endotoxin sensitivity could be explained by the stress of the previous hot summer which might have enhanced the function of the non-specific defence mechanism of the organism. Dietary factors may also have a role in the variation of sensitivity, but this is not definitely proven in this experiment. The chance eliciting the Shwartzman reaction could be enhanced by increasing the provoking dose in the above experiments. The Shwartzman reaction could be elicited by homologous and also heterologous endotoxin. However, the reaction was more marked at the skin site of the heterologous endotoxin preparation. This confirms the immunological specificity in the skin preparation of the Shwartzman reaction.