NCR1+ cells in dogs show phenotypic characteristics of natural killer cells

No specific markers for natural killer (NK) cells in dogs have currently been described. NCR1 (NKp46, CD355) has been considered a pan species NK cell marker and is expressed on most or all NK cells in all species investigated except for the pig which has both a NCR1+ and a NCR1− population. In this study peripheral blood mononuclear cells (PBMC) from 14 healthy dogs, 37 dogs with a clinical diagnosis, including a dog diagnosed with LGL leukemia, and tissue samples from 8 dogs were evaluated for NCR1+ expression by a cross reacting anti bovine NCR1 antibody. CD3−NCR1+ cells were found in the blood of 93 % of healthy dogs and comprised up to 2.5 % of lymphocytes in PBMC. In a selection of healthy dogs, sampling and immunophenotyping were repeated throughout a period of 1 year revealing a substantial variation in the percentage of CD3−NCR1+ over time. Dogs allocated to 8 disease groups had comparable amounts of CD3−NCR1+ cells in PBMC to the healthy individuals. All organs examined including liver, spleen and lymph nodes contained CD3−NCR1+ cells. Circulating CD3−NCR1+ cells were further characterized as CD56−GranzymeB+CD8−. A CD3+NCR1+ population was observed in PBMC in 79 % of the healthy dogs examined representing at the most 4.8 % of the lymphocyte population. In canine samples examined for CD56 expression, CD56+ cells were all CD3+ and NCR1−. To our knowledge, this is the first examination of NCR1 expression in the dog. The study shows that this NK cell associated receptor is expressed both on populations of CD3+ and CD3− blood lymphocytes in dogs and the receptor is found on a CD3+ GranzymeB+ CD8+ leukemia. Our results support that CD56 is expressed only on CD3+ cells in dogs and shows that NCR1 defines a different CD3+ lymphocyte population than CD56+CD3+ cells in this species. CD3−NCR1+ cells may represent canine NK cells.