Bovine WC1− γδT cells incubated with IL-15 express the natural cytotoxicity receptor CD335 (NKp46) and produce IFN-γ in response to exogenous IL-12 and IL-18

Summary The γδ T cells of ruminants are believed to participate in innate immunity and have been described with regulatory, inflammatory and cytotoxic functions. Here we describe a subset of CD3 + TcR1 + WC1 − γδ T cells expressing CD335 (NKp46), classically associated with CD3 − natural killer (NK) cells, as a consequence of incubation with IL-15. This population, undetectable at the time of collection, developed after 2 week of IL-15 culture from splenic leukocytes (SPL) reaching greater than 50% of the total γδ T cells. However, they did not grow well from peripheral blood leukocytes (PBL). Splenic γδ T cells positively selected by magnetic separation prior to incubation with IL-15 and analyzed by flow cytometry, consistently yielded CD3 + cells expressing CD335. These cells arose from the CD335 − γδ T cell population suggesting that the new population represents up-regulation of CD335 by γδ T cells. CD335 mRNA expression from sorted IL-15-incubated SPL CD335 + γδ T cells or NK cells exceeded that of CD335 − γδ T cells. Incubation with IL-12 and IL-18 increased the number of CD335 + γδ T cells in both the PBL and SPL fractions as compared to controls or IL-12 or IL-18 alone. In addition, CD335 + γδ T cells demonstrated a robust ability to produce IFN- γ in response to exogenous IL-12 and IL-18. Taken as a whole, we describe a new phenotypically distinct bovine γδ T cell sub-population capable of participating in type 1 immune responses.