B-Cell Epitopes in the Immunodominant p34 Antigen of Mycobacterium avium ssp. paratuberculosis Recognized by Antibodies from Infected Cattle

OSTROWSKI, M; MUNDO, S.L.; HARRIS, N.B.; BARLETTA, R.G.; LOPEZ, O.J

SCANDINAVIAN JOURNAL OF IMMUNOLOGY

Año: 2003 vol. 58 p. 511 - 521

0300-9475

Mycobacterium avium ssp. paratuberculosis (M. paratuberculosis) causes Johne’sdisease, a chronic and fatal enteritis in ruminants. In the last stage of the disease,antibody titres rise and levels of interferon-g decrease, suggesting that the host–immune response is switching from a T helper 1 (Th1) to a Th2 profile. Ininfected cattle, the membrane protein p34 elicits the predominant humoralresponse against M. paratuberculosis. To map the B-cell epitopes of this antigen,affinity-purified bovine antibodies against the carboxy-terminal region of p34were used to screen a 12-mer phage display library. Several phage clones carryingpeptides resembling fragments of p34 were affinity selected. Based on thepredicted amino acid sequence, peptides were chemically synthesized, whichdemonstrated reactivity with serum from naturally infected and p34-vaccinatedcattle. Immunization of mice with these peptides elicited an anti-p34 antibodyresponse. Two B-cell epitopes were identified and characterized. Based on thereactivity and the type of immune response elicited, epitope A was determined tobe conformational, whereas epitope B was demonstrated to be sequential. Bothepitopes were shown to be present in p34 proteins from M. avium ssp. avium orM. paratuberculosis but absent from M. intracellulare, the other member of theM. avium complex. Furthermore, both epitopes were mapped to regions of p34that display high variability when compared to homologous proteins from othermycobacterial species of public and animal health importance. We hypothesizethat these variable regions of p34 may play a role in the immunobiology ofM. paratuberculosis infections.