Detection of intracellular IFN‐γ and IL‐4 cytokines in CD4+ and CD8+ T cells in the peripheral blood of dogs naturally infected with Leishmania infantum

Canine leishmaniosis (CanL) is a systemic zoonotic disease the clinical manifestations of which can range from self‐healing cutaneous lesions to disseminated visceral disease. Effective activation of cellular immunity is the cornerstone of resistance against Leishmania infantum in infected dogs. The aim of this cross‐sectional, controlled study was the intracellular detection of interleukin 4 (IL‐4) and interferon‐γ (IFN‐γ) in CD4+ and CD8+ lymphocytes in the peripheral blood of 40 dogs naturally infected with L. infantum by applying flow cytometry. The percentage of CD4+IL‐4+ and CD8+IL‐4+ lymphocytes (with or without immunostimulation) was low in the clinically healthy and subclinically infected dogs in contrast to clinically affected ones. In the same groups of dogs, the percentage of CD4+IFN‐γ+ and CD8+IFN‐γ+ T cells in their resting phase and following specific immunostimulation with Leishmania soluble antigen (LSA) was also low. CD4+IL‐4+ and CD8+IL‐4+ T cell percentage was higher in sick compared to clinically healthy and subclinically infected dogs, after immunostimulation. The corresponding figure of CD8+IL‐4+ cells in sick dogs after LSA immunostimulation was also increased thus underlining the important role these cells may play in humoral immunity and perhaps the progression of CanL.