title: Use of antigen-specific interleukin-2 to differentiate between cattle vaccinated with Mycobacterium bovis BCG and cattle infected with M. bovis.
abstract: We describe here the application of a novel bovine interleukin-2 (IL-2) enzyme-linked immunosorbent assay (ELISA) for the measurement of antigen-specific IL-2 in cattle naturally infected with Mycobacterium bovis and in cattle vaccinated with Mycobacterium bovis BCG and then experimentally challenged with pathogenic M. bovis. Supernatants from whole-blood cultures stimulated with mycobacterial antigen (bovine purified protein derivative [PPDB] or the peptide cocktail ESAT6-CFP10) were assessed using a sandwich ELISA consisting of a new recombinant monoclonal fragment capture antibody and a commercially available polyclonal anti-bovine-IL-2. The production of IL-2 was compared to the production of gamma interferon (IFN-γ) in the same antigen-stimulated whole-blood supernatants. The data show that cattle infected with M. bovis produced quantifiable levels of antigen-specific IL-2, while IL-2 levels in cattle vaccinated with M. bovis BCG did not. Furthermore, cattle vaccinated with M. bovis BCG and then challenged with pathogenic M. bovis displayed a more rapid induction of IL-2 but ultimately had lower levels of infection-induced IL-2 than did unvaccinated challenge control cattle. These data suggest that IL-2 responses are not detectable post-BCG vaccination and that these responses may require infection with virulent M. bovis to develop. This may be useful to differentiate infected cattle from uninfected or BCG-vaccinated cattle, although the overall sensitivity is relatively low, particularly in single intradermal comparative cervical tuberculin (SICCT)-negative infected animals. Furthermore, the strength of the IL-2 response may correlate with pathology, which poses interesting questions on the immunobiology of bovine tuberculosis in contrast to human tuberculosis, which is discussed.
authors.affiliation: TB Research Group, Animal Health and Veterinary Laboratories Agency, Surrey, United Kingdom.
authors.forename: Shelley G
authors.initials: SG
authors.lastname: Rhodes
authors.forename: Lucy C
authors.initials: LC
authors.lastname: McKinna
authors.forename: Sabine
authors.initials: S
authors.lastname: Steinbach
authors.forename: Gilly S
authors.initials: GS
authors.lastname: Dean
authors.forename: Bernardo
authors.initials: B
authors.lastname: Villarreal-Ramos
authors.forename: Adam O
authors.initials: AO
authors.lastname: Whelan
authors.forename: C
authors.initials: C
authors.lastname: Pirson
authors.forename: Gareth J
authors.initials: GJ
authors.lastname: Jones
authors.forename: Derek
authors.initials: D
authors.lastname: Clifford
authors.forename: H Martin
authors.initials: HM
authors.lastname: Vordermeier
mesh_terms: D000818:Animals; D001500:BCG Vaccine / Q000008:administration & dosage / Q000276:immunology*; D002417:Cattle; D002478:Cells, Cultured; D019411:Clinical Laboratory Techniques / Q000379:methods*; D003937:Diagnosis, Differential; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods; D007371:Interferon-gamma / Q000378:metabolism; D007376:Interleukin-2 / Q000032:analysis* / Q000378:metabolism; D007963:Leukocytes, Mononuclear / Q000276:immunology; D009163:Mycobacterium bovis / Q000276:immunology*; D014380:Tuberculosis, Bovine / Q000175:diagnosis* / Q000276:immunology*; D014730:Veterinary Medicine / Q000379:methods*
chemical_list: D001500:BCG Vaccine; D007376:Interleukin-2; D007371:Interferon-gamma