A high titer antibody response against P22 protein immunocomplex is not correlated with protection in naturally tuberculosis-infected goats

Abstract

Caprine livestock are significant reservoirs of the Mycobacterium tuberculosis complex (MTBC),contributing to tuberculosis (TB) transmission among animals and humans. The P22 proteinimmunocomplex (P22PI), derived from bovine tuberculin, shows immunostimulating capacityand is used for TB diagnosis. This study assessed the immunogenicity and protective efficacyof P22PI in two groups of goats: 24 naïve goats (12 immunised, 12 controls) from a TB-freeherd, and 24 infected goats (12 immunised, 12 controls), referred to as pre-infected animals,from a M. bovis-infected herd. Both were exposed for 5 months to M. bovis-naturally infectedgoats. Reactors to single and comparative intradermal tuberculin (SIT and SCIT, respectively)tests and interferon-gamma release assay (IGRA) significantly increased (p < 0.05) in bothgroups 5 months’ post-exposure, with no significant differences between immunised andcontrol animals. However, immunised animals exhibited a significantly higher (p < 0.05)antibody response against P22PI. Most naïve animals (83.3%) and all pre-infected animalsdeveloped TB-compatible lesions, with extensive necrosis in the lungs and associated lymphnodes, compared to 50% and 83.3% of control animals, respectively. These findings suggestthat while P22PI stimulates an intense antibody response under the conditions of the presentstudy, it does not confer protection against TB and may exacerbate disease severity.