Effect of the O-Antigen Chemical Structure in Different Subspecies of Francisella Tularensis on Immunological Reactions
The greatest diagnostic significance for tularemia is played by antibodies against lipopolysaccharide (LPS). Previously, it has been shown that specific antibodies that appear in the blood serum of laboratory animals infected with virulent strains and people who have recovered from tularemia can bind both to LPS Francisella tularensis and to LPS Francisella novicida, while after the vaccination specific antibodies to LPS F. novicida are absent. The aim of this work was to investigate the effect of the structure of the O-antigen of lipopolysaccharide F. tularensis of various subspecies on immunological reactions with specific antibodies. The method to isolate LPS from the various F. tularensis strains according to Westphal with modifications was used, and mild acid hydrolysis, and a method of negative contrast in carrying out electron microscopy were used. The ratio of hydrophilic and hydrophobic components of LPS molecules isolated from strains of various subspecies is determined. Correlation of the size of a capsular substance, determined by electron microscopy, with the ratio of hydrophilic and hydrophobic parts in LPS preparations obtained from the same strains was found. It was shown that in virulent strains of F. tularensis the capsule thickness and the ratio of the hydrophilic and hydrophobic parts were higher than those of the vaccine strain 15 NIIEG. Data indicating the presence of a capsule in F. novicida strain were obtained. A hypothesis is proposed that explains the cross-reacting of the sera of humans and animals infected with virulent strains, and with F. tularensis LPS, and with F. novicida LPS.