Abstract
Gene transcription studies have identified dual roles for the cytokines IL-17A and IL-22 in bovine tuberculosis, where they show potential as both predictors of vaccine success and correlates of infection. To allow for a detailed investigation of the cell populations responsible for production of these cytokines, we have utilised a novel bovine IL-22 specific recombinant antibody for flow cytometry. Bovine tuberculin (PPDB) induced greater IL-22 and IL-17A production in Mycobacterium bovis (M. bovis)-infected cattle compared to non-infected controls, while PWM-induced cytokine levels were similar between the two groups. In M. bovis-infected animals, PPDB specific IL-22 and IL-17A responses were observed in both CD4+ T cell and γδ T cell populations. Although both cytokines were detected in both cell types, IL-22/IL-17A double producers were rare and confined mainly to the γδ T cell population. These results support previous gene transcription studies and extend the observation of increased IL-22 and IL-17A responses in M. bovis-infected animals to the level of protein production. We were also able to characterise the cell populations responsible for these disease-related cytokine responses. The data generated can be used to further our understanding of the immunopathology of bovine tuberculosis and to produce more sensitive and specific immune-diagnostic reagents.
Highlights
Mycobacterium bovis (M. bovis), the main causative agent of bovine TB and a member of the M. tuberculosis complex, is capable of causing disease in humans and infecting a wide array of wildlife species, including domestic cattle
To characterise the cellular components that respond to stimulation with mycobacterial antigens by producing IL-17A and/or IL-22, we developed multiparameter flow cytometry panels
These experiments were repeated in a larger number of cattle naturally infected with M. bovis (TB reactors) as well as uninfected control animals to enumerate the percentage of lymphocytes producing either IL-22 (Fig. 2a) or IL-17A (Fig. 2b)
Summary
Mycobacterium bovis (M. bovis), the main causative agent of bovine TB and a member of the M. tuberculosis complex, is capable of causing disease in humans and infecting a wide array of wildlife species, including domestic cattle. In most of the cattle studies detailed above, IL-17A and IL-22 responses were measured from a PBMC population, and the precise nature of the cells responsible for producing these cytokines were undefined Given that both cytokines have been implicated as biomarkers for two very different applications: (i) predictors of vaccine success and (ii) correlates of infection, it is possible that different cell types may be active in these settings. To allow for such future investigations, methodologies must first be established that allow detailed characterisation of these cellular immune responses to M. bovis antigens To this end, we have utilised a novel bovine IL-22 specific recombinant antibody for use in intracellular flow cytometry, which revealed both CD4+T cells and γδT cells as the major producers of IL-17A and IL-22 in the setting of bovine TB
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