CD4+ and γδ T Cells are the main Producers of IL-22 and IL-17A in Lymphocytes from Mycobacterium bovis-infected Cattle

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.

Measuring bovine γδ T cell function at the site of Mycobacterium bovis infection

“…In agreement, Steinbach et al recently described bovine γδ T cells from the periphery as being major producers of IL-22 during infection with M. bovis [43]. Consistent with these previous reports, we measured significant expression of IL-22 in our γδ T cell/macrophage co-cultures; in contrast, however, we observed no expression of IL-22 by γδ T cell within late-stage M. bovis granulomas.…”

“…Consistent with these previous reports, we measured significant expression of IL-22 in our γδ T cell/macrophage co-cultures; in contrast, however, we observed no expression of IL-22 by γδ T cell within late-stage M. bovis granulomas. This is in agreement with Aranday-Cortes et al , who observed a decrease in IL-22 levels by qPCR in late-stage granulomas from M. bovis -infected cattle [43, 44]. Similarly, Palmer et al observed very low levels of expression of IL-22 by RNAScope in any stage of lesion collected at 150 days post M. bovis infection [63].…”

“…We observed that γδ T cells comprise a significant proportion of the cells expressing transcripts for CCL2 within both the lungs and the lymph nodes of infected animals (Figure 2E, Table 5). Expression of IL-10, IL-17, and IL-22 is also upregulated during TB, and γδ T cells have been implicated as a significant source of these cytokines at the site of infection [43–45]. However, in contrast to published reports, we found that fewer than 20% of cells producing IL-10 or IL-17 were γδ T cells (Figure 2 and Table 5), and we observed no γδ T cells expressing IL-22 in the tissues at this stage of infection (data not shown).…”

Controlled Mycobacterium tuberculosis infection in mice under treatment with anti-IL-17A or IL-17F antibodies, in contrast to TNFα neutralization

“…IL-17A is induced in early phases of M. tuberculosis infection14 and contributes to the recruitment of neutrophils1718. Human and animal vaccination studies with M. bovis bacille Calmette-Guérin (BCG) show increased IL-17A responses181920, but specific T cell frequency and cytokine expression profile did not correlate with protection against tuberculosis after BCG vaccination21. The IL-17 pathway seems to be dispensable for low dose M. tuberculosis host resistance1213, while control of a higher inoculum of M. tuberculosis H37Rv1011 or of the hypervirulent M. tuberculosis strain HN878 appears to induce an IL-17A-dependent inflammation, as recently described12.…”

Cattle as Experimental Model to Study Immunopathogenesis of Tuberculosis

“…Indeed, enhanced IL-22 and IL-17A mRNA expression in M. bovis-infected cattle following elicitation with BPPD has also been reported [82] thus proposing that evaluation of these cytokines could be useful biomarkers in bovine infection. To investigate the precise cell populations involved in production of these cytokines, Steinbach et al [83] [74,79]. These observations might be useful for further understanding the immunopathology of bovine TB and to produce more accurate immunodiagnostic reagents.…”