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IgA antibodies to S. sonnei and S. flexneri lipopolysaccharides (LPS) in secretions, as well as Escherichia coli LPS in coprofiltrates of children with acute diarrhea, were determined with the use of enzyme immunoassay (EIA). In adult patients with dysentery serum and salivary anti-LPS antibodies were assayed. The results of EIA showed that children aged up to 18 months had an elevated level of LPS of the causative agent in their coprofiltrates. The specificity of this assay permitted its use for finding out the agent of acute enteric infection. In adults, the levels of salivary anti-LPS antibodies in dysentery patients and in healthy persons significantly differed, which might also be regarded as a sign of Shigella infection. No significant difference in the levels of IgG antibodies to LPS in the saliva of sick and healthy persons was registered. IgA antibodies were found to be active mainly against common determinants of S. sonnei and S. flexneri LPS and thus not suitable for the differentiation of the causative agents of dysentery. For this purpose, the levels of serum IgG antibodies to LPS of different Shigella species should be determined.

The levels of antiribosomal antibodies to Shigella ribosomes in serum and saliva samples from 38 dysentery patients (15 S. sonnei cases and 23 S. flexneri cases), 14 patients with salmonellosis and 136 healthy adults were determined in ELISA with ribosomes from S. sonnei R-mutant used as solid-phase antigen. High levels of "normal" antiribosomal IgA, IgG and IgM antibodies were revealed in the sera of healthy persons while the level of salivary IgA antibodies was very low. In dysentery infection no increase in the levels of serum IgG and IgM antibodies and only a slight increase in the level of IgA antibodies were revealed. Local immune response was manifested by the early (on days 2-4 from the onset of infection) and significant augmentation (12- to 16-fold) of salivary antiribosomal IgA antibodies. An increase in the level of these antibodies was registered in 95-100% of dysentery patients but not in patients with salmonellosis, which made it possible to recommend the method for diagnosing shigellosis. Immune response to Shigella ribosomal antigens, in contrast to the response induced by Shigella O-antigen, is almost exclusively local.

Avidity of Vi-antibodies was studied in the patients suffering from typhoid fever and chronic carriers in the indirect hemagglutination test (IHAT) by means of titration with erythrocytic diagnostic agents sensitized with various doses of the Vi-antigen. The minimal sensitizing dose still adequate for detection of the antibodies in the titre of 1 : 20 was accepted as the avidity index. By the avidity sign the antibody heterogeneity index was calculated as the ratio of the optimal sensitizing dose to the minimal sensitizing one. In comparison with the patients suffering from typhoid fever of at the acute period of the disease in chronic carriers Vi-antibodies were more avid, this being conditioned chiefly by the highly avid IgG-antibodies. During the acute period of the disease the avidity of Vi-antibodies elevated only against the antibodies of the IgG-class. An increase of heterogeneity by the same sign was noted with increase of the degree of the serum antibody avidity.

Specific IgA and sIgA antibodies were studied in the sera of patients suffering from various intestinal diseases (dysentery, salmonellosis, typhoid fever, chronic typhoid carrier state) and in the sera of healthy persons immunized by parenteral route with typhoid alcohol vaccine. The nature of antibodies was identified in Coombs' test, using monospecific antisera to alpha-chain and to the secretory component. IgA and sIgA antibodies were revealed most frequently in the sera of dysentery patients and of chronic typhoid carriers. No sIgA antibodies were found in the sera of subcutaneously immunized persons. The presence of specific sIgA antibodies in the serum reflects the participation of local immune mechanisms in the formation of systemic immunity in the intestinal infections.

The authors studied the immunoglobulin and specific antibodies content of various classes in the serum, coprofiltrates and the saliva of 68 patients suffering from Sonne dysentery and in 48 healthy adult persons. Mancini's test demonstrated a significant elevation of IgG and IgM content in the blood of dysentery patients in comparison with that in healthy persons, and the absence of any changes in the IgA content. The titres of specific IgG-, IgA- and IgM-antibodies in determination in the modified Coombs' test increased consideerably during dysentery infection and were found in high titres during the first week of the disease; they reached the maximum during the second week and persisted at this level for 3 weeks. The greatest antibody elevation was in the IgA-class. Antibodies revealed in the coprofiltrates and the saliva of dysentery patients belonged to IgA- and IgG-class. There proved to be a correlation of the antibody changes in these two secretions.

The accumulation of Vi-antigen in the human body was studied with the use of such characteristic as the specific adsorption capacity of red blood cells. This parameter was shown to depend on the phenotype in the ABO blood group system. In cases of typhoid fever an increase in the adsorption capacity of red blood cells was observed at the acute period of the disease. These changes were particularly manifest in patients belonging to groups O and A. The authors suggest that the adsorption of the antigen on red blood cells has a definite kinetics related to the dynamics of the infectious process.

The study of the adsorption capacity of erythrocytes in 4 strains of mice was made. According to the results of the determination of the background capacity of erythrocytes, the strains of mice, opposite with respect to the sorption of S. typhi Vi- and O-antigens, were selected. After the immunization of these mice with the killed culture of S. typhi, the process of the sorption of the antigen on erythrocytes showed a characteristic kinetics. The course of immune response was characterized by specific changes in the adsorption capacity of erythrocytes in all strains of mice: the increase of this capacity on week 1 was followed by its sharp drop on weeks 3-4 and its subsequent restoration to the initial level by weeks 7-8. The non-specific stimulation of the host had no essential influence on the kinetics of the fixation of S. typhi antigens on erythrocytes. Experiments with the passive immunization of the animals revealed that different receptors take part in the process of the sorption of Vi-antigen on erythrocytes, some of these receptors being related to antibodies.

A study was made of the dynamics of serum H-antibodies in typhoid patients depending on the period of the disease and the severity of its course; the blood sera of chronic carriers were examined as well. H-antibodies were determined in the indirect hemagglutination test with the use of erythrocyte H-dignoasticum. Antibodies of different physico-chemical nature (of IgG and IgM classes) were obtained by fractionation in columns with DEAE-cellulose. Results of the investigations showed that the titres of sum total serum H-antibodies failed to depend on the severity of the course of the disease. The maximum value of the mean geometrical titre of H-antibodies in the blood serum was determined on the 3rd-4th week from the onset of the disease. In chronic carriers the sum total H-antibody titres were greater than in typhoid patients. The serum H-antibody titres increased on account of IgG-globulins both in the typhoid patients and in carriers.

The ability of erythrocytes to absorb Vi-antigen at optimal (Sopt) and minimal (Smin) sensitizing doses in 52 patients suffering from enteric fever and 61 healthy individuals was studied. Smin has been found to be independent of ABO phenotype of both ill and healthy individuals. At the same time Sopt is considerably reduced in patients having A blood group as compared to healthy individuals. Relationship between antigen binding rigidity with erythrocyte receptors and individual blood groups has been determined.