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

## TL;DR

This study shows that a modified TbpB vaccine can boost T-cell immunity in piglets against Glaesserella parasuis, a harmful bacteria, by inducing strong and timely immune responses.

## Contribution

The study reveals the temporal dynamics of T-cell subsets in response to a TbpBY167A vaccine in piglets, highlighting key immune mechanisms for protection.

## Key findings

- Booster vaccination significantly increased B cells, TCRγδ T cells, CD8+ αβ T cells, and CD4+ memory T cells.
- CD8+ cytotoxic T cells in vaccinated piglets rapidly transitioned to memory phenotypes after infection.
- The observed T-cell dynamics correlate with previously demonstrated protective efficacy of the vaccine.

## Abstract

Glaesserella parasuis is an important cause of respiratory and systemic disease in piglets, leading to animal welfare issues and economic losses in pig production. The high antigenic diversity of this bacterium makes it difficult to develop vaccines that provide broad and reliable protection. In this study, colostrum-deprived piglets were vaccinated with a genetically modified form of a bacterial surface protein that is involved in iron acquisition, and later exposed to infection under experimental conditions. Blood samples were collected at different time points to analyze how the immune system responded to vaccination and subsequent infection. Vaccinated animals showed a marked increase in several lymphocyte populations, including cells with cytotoxic activity and cells with a long-lasting response to the pathogen. These changes were observed only after booster vaccination and again shortly after infection, and were associated with protection against disease. Overall, these findings indicate that this vaccine candidate can stimulate a coordinated cellular immune response that may contribute to improved control of Glaesserella parasuis infections in pig herds.

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.