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

Abstract

The γδT 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- γδT 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 γδT cells. However, they did not grow well from peripheral blood leukocytes (PBL). Splenic γδT 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- γδT cell population suggesting that the new population represents up-regulation of CD335 by γδT cells. CD335 mRNA expression from sorted IL-15-incubated SPL CD335+ γδT cells or NK cells exceeded that of CD335- γδT cells. Incubation with IL-12 and IL-18 increased the number of CD335+ γδT cells in both the PBL and SPL fractions as compared to controls or IL-12 or IL-18 alone. In addition, CD335+ γδT 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 γδT cell sub-population capable of participating in type 1 immune responses.