Flow cytometric detection of gamma interferon can effectively discriminate Mycobacterium bovis BCG-vaccinated cattle from M. bovis-infected cattle.
Mycobacterium bovis is the causative agent of bovine tuberculosis, a disease that is increasing in incidence in United Kingdom cattle herds. In addition to increasing economic losses, the rise in bovine tuberculosis poses a human health risk. There is an urgent requirement for effective strategies for disease eradication; this will likely involve vaccination in conjunction with current test and slaughter policies. A policy involving vaccination would require an accurate diagnosis of M. bovis-infected animals and the potential to distinguish these animals from vaccinates. Currently used diagnostic tests, the skin test and gamma interferon (IFN-gamma) blood test, have a sensitivity of up to 95%. A further complication is that M. bovis BCG-vaccinated animals are also scored positive by these tests. We tested the hypothesis that the quantification of IFN-gamma-producing lymphocytes by flow cytometric analysis of intracellular IFN-gamma expression would provide a more accurate discrimination of M. bovis-infected animals from BCG vaccinates. Significant numbers of IFN-gamma-expressing CD4+ T cells were detected following culture of heparinized blood from M. bovis-infected animals, but not from BCG vaccinates, with purified protein derived from M. bovis (PPD-B) or live mycobacteria. Only 1 of 17 BCG-vaccinated animals had a significant number of CD4+ T lymphocytes expressing IFN-gamma, compared with 21/22 M. bovis-infected animals. This assay could allow an accurate diagnosis of M. bovis and allow the discrimination of BCG-vaccinated cattle from infected cattle.
Sopp
P
P
Institute for Animal Health, Compton, Newbury, Berkshire RG207NN, United Kingdom.
Howard
C J
CJ
Hope
J C
JC
D000818:Animals; D001500:BCG Vaccine / Q000008:administration & dosage / Q000276:immunology*; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology / Q000378:metabolism*; D002417:Cattle; D005434:Flow Cytometry / Q000379:methods*; D007371:Interferon-gamma / Q000378:metabolism*; D009163:Mycobacterium bovis / Q000145:classification / Q000276:immunology*; D014380:Tuberculosis, Bovine / Q000175:diagnosis* / Q000276:immunology / Q000517:prevention & control; D014611:Vaccination
D001500:BCG Vaccine; D007371:Interferon-gamma