Structural and Serological Studies of the O-Antigen of the Bacterium Proteus vulgaris OX2 (Serogroup O2) Used in the Weil--Felix Test

M. Cedzynski,¹ Yu. A. Knirel,^2,3 K.-I. Amano,⁴ A. S. Swierzko,¹ N. A. Paramonov,² S. N. Senchenkova,² and W. Kaca¹

¹Center of Microbiology and Virology, Polish Academy of Sciences, ul. Lodowa 106, 93-232 Lodz, Poland; fax: (48-42) 49-16-33.

²Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, Leninskii pr. 47, Moscow V-334, GSP-1, 117913 Russia; fax: (7-095) 135-53-28; E-mail: knirel@ioc.ac.ru

³To whom correspondence should be addressed.

⁴Central Research Laboratory, School of Medicine, Akita University, 111, Hondo, Akita 010, Japan.

Submitted September 20, 1996.

Based on monosaccharide analysis and ¹H- and ¹³C-NMR spectroscopy, the following structure of the O-specific polysaccharide chain of Proteus vulgaris OX2 lipopolysaccharide (LPS), which defines the O2 specificity of Proteus, was established: (see full article for figure), where L-QuiNAc is N-acetyl-L-quinovosamine (2-acetamido-2,6-dideoxy-L-glucose). Various strains of P. vulgaris OX2 used in the Weil--Felix test for serodiagnosis of rickettsiosis (spotted fevers, except for Rocky Mountain spotted fever) were shown to produce LPS with the same O-specific polysaccharide, which differs structurally and serologically from LPS of P. vulgaris OX19 used as antigen for serodiagnosis of typhus and Rocky Mountain spotted fever. O-Acetyl groups present in the polysaccharide are not important for manifesting the immunospecificity. ELISA confirmed that the epitope responsible for the cross-reactivity between sera from patients with Japanese spotted fever and P. vulgaris OX2 cells is located on the P. vulgaris LPS. At the same time, no cross-reaction was observed between rabbit anti-P. vulgaris OX2 antibodies and the spotted fever group (SFG) rickettsial cells. Therefore, human anti-SFG rickettsial antibodies 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 surface antigen of SFG rickettsiae.

KEY WORDS: lipopolysaccharide, O-specific polysaccharide, structure, serological cross-reactivity, spotted fever, Weil--Felix test, Proteus vulgaris, Rickettsia.

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