[Phase variations of Francisella tularensis lipopolysaccharide in human infection and immunization]

The comparative study of the specificity of antibodies in human sera after tularemia infection and immunization with live tularemia infection was carried out with the use of passive hemagglutination and immunoblotting techniques. The sera of tularemia patients contained two different types of immunoglobulins: strictly specific to the antigenic epitopes of F. tularensis Iipopolysaccharide (LPS) and strictly specific to F. tularensis subsp. novicida LPS. Such phenomenon may be due to phase variations of the antigenic structure of F. tularensis LPS in the body of a slightly susceptible host. The immune sera of vaccinated were found to contain antibodies, strictly specific only to F. tularensis LPS. At the same time in one vaccinee by the presence of pronounced postvaccinal reactions was found sharply defined interaction between serum imunoglobulins and F. tularensis subsp. novicida LPS. As the result, the data on the possibility of the antigenic modification of F. tularensis in tularemia infection in humans were obtained. At the same time antigenic epitopes, characteristic of faintly pathogenic and closely related F. tularensis novicida LPS, appeared in the structure of F. tularensis LPS.