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In the course of chronic carrier state of El-Tor vibrio cholerae gnotobiotic rats develop an immunomorphological reaction in the mucous membranes of the small and large intestines, Peter's patches, and mesenterial lymph nodes consisting in activation of reactive centers of follicles, hyperplasia of reticular cells, and an increase in the number of pyroninophilic plasma cells. The vibrio cholerae caused no pathological changes in enterocytes and other cells but its inoculation was accompanied by a "minor inflammation" in the intestinal wall and mesenterial lymph nodes. Eosinophilic infiltration in the intestinal tract, intensive mast cell reaction with degranulation in the small and large intestines and regional lymph nodes was observed.

Many authors have demonstrated simplification of the species composition of the normal microflora in animals long kept in a closed environment. The purpose of the present work is to reveal the effect of such simplification (without reduction of the total number of bacteria) on the immunocompetent system of the animals. Three months old germ-free, monocontaminated (Staph. albus) and conventional guinea pigs with reduced fecal microflora were used in this study. Guinea pigs of the second group were fed a sterile diet but were kept in an ordinary vivarium. Two groups of control animals were: 1) conventionals fed regular diets; 2) conventionals fed the diet contaminated with fecal microflora of guinea pigs after sterilization. The fecal microflora was examined. The total number of bacteria in faeces of monocontaminated and microflora-reduced conventional animals was approximately the same as in conventional controls. Various lymphoid organs were examined. Their weight, size, number and activity of germinal centres, amount of globulin-producing cells, their differentiation and amount of globulins in single cells were determined. The lymphoid tissue in microflora-reduced animals and especially in monocontaminated guinea pigs was found to be underdeveloped. These changes were, however, less pronounced than in germ-free animals. It is suggested that simplification of the microflora in a macro-organism during long-term enclosure reduces the lymphoid tissue; such a macro-organism may develop severe reactions of the microbial shock, when occurring in a normal microbial environment.