Bovine WC1(+) γδ T lymphocytes modify monocyte-derived macrophage responses during early Mycobacterium avium subspecies paratuberculosis infection

Following Mycobacterium avium subspecies paratuberculosis (Map) infection, some calves are apparently able to successfully clear the pathogen whereas others become persistently infected; however the reasons for this remain unknown. The importance of innate immunity, and in particular the role of γδ T lymphocytes, during early anti-mycobacterial immune response is recognized but specific mechanisms remain incompletely characterized. The objective of this study was to investigate how bovine WC1(+) γδ T lymphocytes mediate macrophage function during early Map infection. To achieve this objective, Map-infected monocyte-derived macrophages (MDMs) were co-cultured either in direct contact with, or separated by a semi-permeable membrane from, autologous WC1(+) γδ T lymphocytes. Nitrites, IL-17A, IFN-γ, IL-4 and IL-10 from cell culture supernatants were measured. Expression of CD25 on WC1(+) γδ T lymphocytes, expression of MHC-I and MHC-II on MDMs and the viability of Map recovered from MDM cultures 72h after Map infection were also assessed. Map viability was significantly reduced when WC1(+) γδ T lymphocytes were co-cultured in direct contact with Map-infected MDMs. Both MDMs and WC1(+) γδ T lymphocytes generated increased concentrations of IFN-γ and IL-4 in our system, and MDM/WC1(+) γδ T lymphocyte synergism was identified for IFN-γ production. MDMs but not WC1(+) γδ T lymphocytes were a significant source of IL-17A. The presence of WC1(+) γδ T lymphocytes was associated with higher expression of MHC-I on MDMs and increased concentration of nitrites in supernatants 72h after Map infection. In conclusion, this study showed that WC1(+) γδ lymphocytes had differential effects on Map-infected macrophages in vitro.