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Individuals of the Le(b+)/secretor phenotype revealed a stronger natural immune response to Le(x) and Le(y) epitopes irrespective of Helicobacter pylori serologic status. In contrast, H. pylori-infected Le(b-) type individuals showed a significantly higher proportion of strong responders to Le(x) antigen compared with the H. pylori-uninfected subgroup. The data suggest that the immune response to Lewis type 2 determinants is related to both the H. pylori serologic status and the Le(a,b) phenotype of the host.

A possible association of serum anti-T IgM and IgG antibody levels with Lewis blood-group phenotype was investigated in 168 blood donors and 132 gastric cancer patients using ELISA with synthetic T-disaccharide-polyacrylamide conjugate as antigen. The donors of Le(a-b+) phenotype showed the highest anti-T IgM level irrespective of ABO(H) blood group. A significant decrease in anti-T IgM in serum was observed among cancer patients of Le(a-b+) phenotype: 95% of weak responders versus 17.5% for related groups of donors (p < 10(-6)). In contrast, no significant difference between patients and donors was found for Le(b-) individuals. Thus, a level of natural anti-T antibodies in serum of blood donors and its decrease in patients with gastric cancer are related to Le(a,b) phenotype. This should be taken into account where anti-T antibody level in the serum is used as a tumour marker or for monitoring patients during cancer immunotherapy with mucin-type vaccines.

For studying the dynamics of induction and disappearing of complement-fixing antibodies (CFA) specific to Trichomonas vaginalis, T. hominis and T. tenax we have immunized rabbits intravenously with live individuals of the protozoa as well as intravenously, intramuscularly and subcutaneously with individuals killed at 56 degrees C. Each method of immunization was carried out by 5 inoculations with intervals of 10 days. For carrying out quantitative complement fixation we have taken blood from the ear vein of all immunized rabbits immediately before the immunization and also after it, each 10th day during one year. The dynamics of rising and lowering of titres depended on the species of trichomonads and on the method of immunization. The antigens of T. vaginalis and T. hominis induced CFA in much higher titres as antigens of T. tenax. Titres of CFA specific for all three species of above-mentioned trichomonads rose most rapidly and to the highest level when the immunization of rabbits was carried out intravenously with live individuals of protozoa. Normalization of the titres of CFA has taken place during one year at least.