OspA epitopes involved in binding. (a) Relative binding of overlapping OspA peptides (100 μL of 5 μg/mL peptide) to TGE. The background binding of FITC (F) to TGE has been indicated. The mean ± SD of three experiments is shown. (b) Inhibition of labeled OspA peptide binding to TGE by unlabeled OspA. TGE was probed with 100 μL of FITC-labeled OspA peptide (5 μg/mL) in the absence (black bars) or presence (white bars) of 250 μg/mL of unlabeled OspA. The mean ± SD of two experiments using OspA from B. burgdorferi N40 is shown. (c) OspA_229–247 and peptide OspA_85–103 bind to the same site, or effectively inhibit binding of a second site, in the tick gut. TGE was probed with 20 μg/mL of FITC-labeled OspA_85–103 or OspA_229–247 in the absence (black bars) or presence of competitor, 1 mg/mL of unlabeled OspA_229–247 or OspA_85–103, respectively (gray bars). Control studies used BSA as a competitor (white bars). The mean ± SD of six experiments is shown. (d) Amino acid polymorphism in OspA_85–103 and OspA_229–247. Comparison of the B. burgdorferi N40 and B. burgdorferi 25015 sequences (variable amino acids are indicated by asterisks). Seventy-nine OspA sequences available in GenBank were aligned, and the strictly conserved residues are presented in bold face. Single-letter abbreviations for the amino acid residues are indicated in Table 1.