Babesia bovis-specific T CD4+ cell clones from immune cattle express either the ThO or Th1 profile of cytokines

Abstract

The central role of T cells in the immune response against hemoprotozoan parasites, both as helper cells for T-dependent antibody production, and as effect or cells acting directly or indirectly on intracellular parasites through the elaboration of cytokines, has prompted us to investigate the bovine cellular immune response against B. bovis antigens. T cell clones generated from four B. bovis-immune cattle by in vitro stimulation with soluble or membrane associated merozoite antigen were characterized for reactivity against various forms of antigen and different geographical isolates of B. bovis and B. bigemina. The clones were categorized into seven different groups based on differential patterns of reactivity. This panel of T cell clones and additional clones specific for either the 77 kDa merozoite apical complex associated protein (Bb-1) or the 42 kDa major merozoite protein (MSA-1) were analyzed for cytokines. Biological assays to measure IL-2/IL-4, IFN-γ and TNF-α /TNF-β and Northern blot analysis to detect mRNA encoding bovine IL2, IL-4, IFN-γ, TNF-β and TNF-α revealed the differential production of cytokines by clones with different antigen specificities. Two Bb-1-specific T cell clones produced the Th1 pattern of cytokines: IL-2, IFN-γ, TNF-β and TNF-α, but not IL-4. Clones specific for the 42 kDa protein produced undetectable levels of all cytokines, but expressed an unrestricted or Th0 pattern of cytokine mRNA: IL-2, IL-4, IFN-γ and TNF-α. Finally, the majority of Th clones reactive with undefined merozoite antigens expressed the Th0 pattern of cytokines, and several clones were of the Th1 phenotype, whereas none of the clones expressed a Th2 profile of cytokines. Because in other protozoal infections Th1 cells, IFN-γ, TNF-α, and TNF-β, but not IL-4 are associated with the development of a protective immunity, Bb-1 is a logical candidate for a B.bovis vaccine.