We describe the isolation of the gene encoding a 22-kDa antigen from Borrelia burgdorferi, the etiologic agent of
Lyme disease. The p22 gene is 582 nucleotides in length and encodes a protein of 194 amino acids with a predicted molecular mass of 21.8 kDa. The leader signal sequence of P22 consists of a positively charged short amino terminus, a central hydrophobic domain, and at the carboxyl terminus, a cleavage site that is presumably recognized and cleaved by a B. burgdorferi signal peptidase. P22 has 98.5% homology with the recently described B. burgdorferi protein IpLA7. P22 is processed as a lipoprotein, as demonstrated by [3H]palmitate labeling. Pulsed-field gel electrophoresis showed that p22, like LA7, is localized to the linear chromosome of B. burgdorferi. Examination of sera from patients with
Lyme disease revealed that antibodies to P22 are rarely detected in patients with early-stage
disease characterized by erythema migrans (2 of 20), and 35% of the patients with late-stage
disease characterized by arthritis (9 of 26) developed antibodies to P22. Sera from patients with syphilis did not react with P22. When patients with late-stage
disease were tested for their antibody reactivities to four other outer surface proteins (OspA), OspB, OspE, and OspF), 75% of these patients responded to P22 or to one or more outer surface proteins.