NKP46 Marks caprine natural killer cells but is also present on some CD3 and TCR delta cells
Résumé
NKp46 has proven a reliable NK cell marker in both cattle and sheep. Four anti-bovine/ovine NKp46 mAbs reacted to caprine lymphocytes and specificity was confirmed as all mAbs reacted with caprine NKp46 transfectants. At young ages, goat NKp46+ cells were scarcer in circulation (~1% of PBMC) than in cattle and sheep, but the numbers increase with age. Similar to cattle and sheep, these cells are CD16+, CD8+, moderately perforin+, and CD2 marks a major negative and a minor positive subset. NKp46+ cells produce IFN-γ in response to cytokine stimulation, and following positive selection and culture they upregulate perforin and respond with NKp46-mediated cytotoxicity, thus confirming typical NK cell functions. NKp46 expression was non-overlapping with CD21+ B-cells, CD4+ T-cells and CD14+ monocytes. Most caprine-reactive gamma/delta TcR antibodies do not mark NKp46+ cells. However, in older goats, a significant proportion of NKp46+ cells express the TcR delta chain. This occurs at an age where the proportion of classical gamma-delta T-cells is in decline. NKp46+/TcRdelta+ cells were also present in cultures of IL-2 expanded caprine NKp46+ cells. Since NK cells in most species are CD3-/NKp46+, we stained permeabilized caprine PBMCs with a human cytoplasmatic CD3 epsilon mAb, which is cross-reactive in several species. Staining patterns corresponded well with expected T-cell populations, but this mAb also stained a subset of NKp46+ cells, the majority of which were also TcRdelta+. Thus, cytCD3e cannot be used straightforward for NK cell discrimination in goats, and these overlapping populations need closer investigation.