Temporal Dynamics of T Cell Immunity Induced by TbpBY167A Vaccine in Colostrum-Deprived Piglets Challenged with Glaesserella parasuis

Glaesserella parasuis (G. parasuis) is a key pathogen responsible for swine respiratory disease, and the development of broadly protective vaccines is hampered by its high antigenic diversity. The iron-acquisition protein TbpB is a conserved vaccine candidate, but the cellular immune responses it elicits, particularly T-cell subset dynamics during immunization and challenge, remain insufficiently defined. This study characterized these responses after oral immunization of colostrum-deprived piglets with the TbpBY167A mutant. Ten colostrum-deprived piglets were allocated to immunized and non-immunized (PBS) groups, immunized at days 15 and 30 of life and subsequently challenged with G. parasuis (45 days old); peripheral blood mononuclear cells were collected at baseline, after each immunization, and at 1 and 3 days post-infection. Multiparametric flow cytometry was used to quantify major leukocyte subsets and T-cell phenotypes defined by sIgM, CD172a, CD3, TCRγδ, CD8α/β, CD4 and CD27 expression. Booster immunization induced significant expansion of B cells (p < 0.01), TCRγδ T cells (p < 0.01), CD8+ αβ T cells (p < 0.001) and CD4+ memory T cells (p < 0.01) in immunized piglets compared with controls. After challenge, CD8+ cytotoxic T cells in immunized animals rapidly shifted from naïve to memory phenotypes, peaking at 48–72 h (p < 0.01). These biphasic T-cell dynamics are consistent with the protective efficacy previously demonstrated for this vaccine in colostrum-deprived piglets, and support a key contribution of TCRγδ, CD8+ cytotoxic and CD4+ memory T cells to immunity against G. parasuis and to the design of next-generation vaccines.