FIG. 6.

Immunoreactivity with PA and with the 305-319 peptide from sera of rabbits immunized with PA. Seven rabbits received priming immunizations with PA in CFA and then were boosted 2 weeks later with PA in IFA (A), and four rabbits received priming immunizations with PA in Alhydrogel and were boosted twice at 2-week intervals (B). Ten days after the final booster immunization (day 24 for rabbits in panel A and day 34 for rabbits in panel B), rabbits were bled and individual rabbit sera (circles) were analyzed for immunoreactivity with either PA, the 305-319 peptide, or an irrelevant peptide sequence. For analysis of peptide reactivity, a recombinant protein displaying two copies per molecule of aa 305 to 319 of PA or an irrelevant peptide sequence was immobilized on the ELISA plates as described in Materials and Methods. As a positive control, the immunoreactivity of the sera from four MAP peptide-immune rabbits (triangles) is also shown in panel A. There was no significant difference in GMT observed in the sera of the rabbits immunized with PA in Freund's (A) upon testing with either the immobilized 305-319 peptide or the irrelevant peptide sequence (P = 0.8513; Student's t test). The lower limit of assay detection for the ELISA is 16; samples below this limit are plotted at 16. Horizontal lines represent GMTs.