The potential role of vitamin D in the immune response to bovine tuberculosis

Abstract

The role of vitamin D in the immune response of cattle, particularly in the context of bovine tuberculosis (bTB), remains underexplored. This thesis investigated the impact of circulating vitamin D concentrations on immune responses and disease outcomes in cattle from herds with both recurrent bTB in their natural environment, and cattle experimentally infected with Mycobacterium bovis (M. bovis). Chapter 1 aimed to evaluate the variation in plasma vitamin D levels and their influence on cytokine expression. Plasma samples from nine herds in Northern Ireland and the Republic of Ireland (n=495) revealed a mean vitamin D concentration of 31.92 ng/ml, with 42% of samples below the optimal threshold of 30 ng/ml. Peripheral blood mononuclear cells (PBMCs) cultured in serum from low (< 30 ng/ml) and high (51.93 ng/ml) vitamin D groups and stimulated with M. bovis purified protein derivative showed no significant difference in cytokine expression of IL-1β, IL-6, and IL-8 at 12 hours post-stimulation. These findings suggest that current circulating vitamin D levels may not strongly influence innate cytokine expression, which could have implications for bTB disease progression.

Chapter 3 investigated the association between vitamin D concentration, TB vaccination, and M. bovis infection outcomes in dairy calves. The study comprised two phases: vaccination (week 0-52) and experimental infection (week 52-65). Twenty-eight calves, vaccinated (n=14) or unvaccinated (n=14), were infected with 7,600 CFU of M. bovis post-vaccination. Serum 25(OH)D concentrations were measured at intervals using ELISA. Post-infection, vaccinated calves exhibited significantly higher 25(OH)D concentrations compared to non-vaccinates. Higher 25(OH)D levels were associated with lower pathology scores, regardless of vaccination status, indicating a negative linear relationship. A significant effect of 25(OH)D concentrations on lymph node pathology was observed at week 62 and a tendency at week 65. No correlation was found between interferon-γ production and vitamin D concentration.

Overall, these studies highlight the crucial role of vitamin D in modulating immune responses and reducing disease severity in cattle infected with M. bovis. The insights gained underscore the potential for optimising TB vaccination protocols and developing novel TB control strategies through vit D supplementation, offering promising avenues for enhancing bovine health management.

Date of Award	Dec 2024
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Higher Education Authority
Supervisor	Ilias Kyriazakis (Supervisor) & Kieran Meade (Supervisor)