Biochemical and immunological properties of Coxiella burnetii cell wall and peptidoglycan-protein complex fractions

Abstract

Coxiella burnetii morphological cell types were fractionated into large-cell variant cell walls, two fractions of small-cell variant cell walls, and one fraction of small-cell variant whole cells. Based on the contents of peptidoglycan (PG)-constituents and the yields of the sodium dodecyl sulfate-insoluble PG-protein complex (PG-PC) from cell walls, the fraction of large-cell variant cell walls contained significantly less PG than did the fraction of small-cell variant cell walls. The yields of PG-PC from the fractions of large-cell variant cell walls and small-cell variant cell walls were 2 and 32%, respectively. These results indicated that the PG of the large-cell variant cell walls may be partially digested by PG-lytic enzymes or incompletely synthesized, whereas the small-cell variant cell walls appeared to have intact PG. Proteins associated with PG-PC were resistant to proteolysis by trypsin, protease VI, and proteinase K. Saturated and unsaturated fatty acids were detected in whole cells and cell walls but not in PG-PC, which contained a 3-deoxy-D-mannooctulosonic acid-like component that is also present in phase I lipopolysaccharide. Immunogenicity of the fractions was tested by measuring the temporal sequence of phase II and phase I antibody responses in vaccinated rabbits. Both phase II and phase I antibody responses were demonstrated with all fractions except the sodium dodecyl sulfate supernatant of the small-cell variant cell walls, whereas PG-PC elicited a pure phase II antibody response up to 29 days postvaccination. The immunogenicity of these fractions may reflect a quantitative difference in antigen concentration or may be due to a qualitative difference in phase II and I determinants.