We have found that sera from patients with early stages of
Lyme disease contain predominant
immunoglobulin M reactivity to a major 23-kDa
protein (p23) from Borrelia burgdorferi 2591 isolated in Connecticut. To characterize this immunodominant
antigen, we cloned and sequenced
p23 and found it to be 83% identical by nucleotide sequence and 75% identical by
amino acid sequenced to pC (recently renamed
OspC), an abundantly expressed
protein on the outer surface of PKo, a European strain of B. burgdorferi (B. Wilske, V. Preac-Mursic, S. Jauris, A. Hofmann, I. Pradel, E. Soutschek, E.Schwab, G. Will, and G. Wanner, Infect. Immun. 61:2182-2191, 1993). In addition, immunoelectron microscopy localized
p23 to the outer membrane, confirming that
p23 is the strain 2591 homolog of
OspC. The North American strain B31, commonly used in serologic assays for
Lyme disease, does not express
OspC. Northern (
RNA) blot analysis detected low levels of
ospC mRNA in B31, and
DNA sequencing of the
ospC gene from B31 revealed a 54-bp deletion in the upstream regulatory region, possibly accounting for the low transcriptional activity of
ospC. The
ospC coding region from B31 was cloned and antibody-reactive
OspC was expressed in Escherichia coli. An
immunoglobulin M enzyme-linked
immunosorbent assay using recombinant
OspC as the target
antigen shows promise for the serodiagnosis of early stages of
Lyme disease.