Lack of correlation between BCG-induced tuberculin skin test sensitisation and protective immunity in cattle

Cellular immune response of Curraleiro Pé-duro and Nellore calves following Mycobacterium bovis-BCG vaccination

“…Yet, the use of the skin test as a clinical indicator of successful BCG--induced protective immunity is controversial. Whelan et al (2011) found that the loss of the TST reaction after BCG vaccination was not correlated with loss in protection on neonate calves. The TST and IFN-γ responses are both predictive of infection, however the relationship between the two responses is not so clear.…”

“…The specific IFN-γ production is often used for accessing vaccine responses. In TB context, however, the IFN-g is also correlated with lesion scores (i.e severity of disease) and has been used as a diagnostic tool, in enzyme-linked immunosorbent spot (ELISpot) assay and in blood-based in vitro laboratory test, as the Bovigam test (Vordermeier et al 2006, Whelan et al 2011. The release of IFN-g in infected cattle may be caused by the bacterial burden during later stages of infection, after the immune control of the pathogen has failed, leading to the destructive effects of Th1 response on tissues.…”

“…BCG is currently used for human vaccination against tuberculosis (TB) and experimentally used in cattle (Buddle et al 2005, Kaufmann et al 2006. The BCG vaccination elicits strong cellular mediated immune (CMI) response without causing clinical disease (Waters et al 2009, Whelan et al 2011, Chan et al 2013. The main tools for human and bovine TB diagnosis are tuberculin skin test (TST) reaction to purified protein derivated from M. bovis culture (bPPD), as well as, specific IFN-g production (i.e., T helper 1 response, Th1) after antigenic stimulation.…”

Immunity and Vaccination against Tuberculosis in Cattle

“…Detection of a delayed type-hypersensitivity (DTH) response to tuberculin is used as the primary screening tool for detection of TB in cattle, although there is not a consistent correlation with protection post-vaccination. Most effective vaccines elicit a DTH response, and non-sensitising vaccines such as low oral doses of BCG have not been shown to induce protection [56], although maintenance of a DTH response is not linked with protection [49]. Serological responses to mycobacterial antigens have not been linked with protection post-vaccination as shown when TB protein vaccines were used alone, whereas when TB protein vaccines are used concurrently with a BCG vaccine, protection was not adversely affected by the induction of an antibody response [45].…”

“…Vaccination with TB vaccines can compromise the interpretation of the tuberculin skin test, and up to 80 % of BCGvaccinated calves have been shown to react in the tuberculin skin test at 6 months post-vaccination [49]. Encouragingly, this decreased to 10 -20 % by 9 months post-vaccination and protection against TB was not dependent on maintenance of a tuberculin skin test response.…”