Cytokine profile of protective anti‐Trichinella spiralis CD4+ OX22− and non‐protective CD4+ OX22+ thoracic duct cells in rats: secretion of IL‐4 alone does not determine protective capacity

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Abstract
SUMMARY: We analysed the cytokine profile of a T cell subset (CD4+ CD45 RC−) that confers protection against Trichinella spiralis infection in rats. These CD4+ cells are generated in the gut and appear in the thoracic duct lymph within 72 h after infection. Cytokine mRNA levels for IL‐2, IL‐3, IL‐4, IL‐5, IL‐10 and IFN‐γ and functional cytokine secretion for IL‐4, IL‐5, IFN‐γ, TNF‐α and mast cell differentiation activity were tested in vitro following stimulation with T. spiralis antigens. Compared to a non‐protective T cell population (CD4+ CD45 RC+ or CD8+), also isolated from the same thoracic lymph, no significant differences were observed in the levels of mRNA for IL‐2, IL‐3, IL‐4, IL‐5, IL‐10 or IFN‐γ in the protective CD4+ CD45 RC− cells. However, analysis of the cytokine activities in culture supernatant of these T cell subsets following 24 h stimulation in vitro with T. spiralis antigens showed that significant IL‐4 and IL‐5 activity but little IFN‐γ or TNF‐α was secreted by the protective CD4+ CD45 RC− cells. Whereas the non‐protective CD4+ CD45 RC+ cells secreted significant levels of IL‐4, IFN‐γ, mast cell differentiating activity and TNF‐α but little IL‐5 activity. Nonprotective CD8+ cells were found to secrete IL‐4 but not IL‐5. Production of IL‐4 was essentially equal for both protective and non‐protective T cell subsets. These findings suggest that the presence or absence of IFN‐γ secretion, rather than IL‐4 alone, determines whether a T cell subset has protective activity against T. spiralis infection in rats.