STRUCTURAL AND SEROLOGICAL STUDIES OF THE O-ANTIGEN OF THE BACTERIUM PROTEUS-VULGARIS OX2 (SEROGROUP O2) USED IN THE WEIL-FELIX TEST

Based on monosaccharide analysis and H-1- and C-13-NMR spectroscopy, t he following structure of the O-specific polysaccharide chain of Prote us vulgaris OX2 lipopoiysaccharide (LPS), which defines the O2 specifi city of Proteus, was established: [GRAPHICS] where L-QuiNAc is N-acety l-L-quinovosamine (2-acetamido-2,6-dideoxy-L-glucose). Various strains of P. vulgaris OX2 used in the Weil-Felix test for serodiagnosis of r ickettsiosis (spotted fevers, except for Rocky Mountain spotted fever) were shown to produce LPS with the same O-specific polysaccharide, wh ich differs structurally and serologically from LPS of P. vulgaris OX1 9 used as antigen for serodiagnosis of typhus and Rocky Mountain spott ed fever. O-Acetyl groups present in the polysaccharide are not import ant for manifesting the immunospecificity. ELISA confirmed that the ep itope responsible for the cross-reactivity between sera from patients with Japanese spotted fever and P. vulgaris OX2 cells is located on th e P. vulgaris LPS. At the same time, no cross-reaction was observed be tween rabbit anti-P. vulgaris OX2 antibodies and the spotted fever gro up (SFG) rickettsial cells. Therefore, human anti-SFG rickettsial anti bodies and rabbit anti-P, vulgaris OX2 antibodies may bind to distinct epitopes on P. vulgaris OX2 LPS, and no epitope recognized by rabbit anti-P. vulgaris OX2 antibodies is present on the LPS or any other sur face antigen of SFG rickettsiae.