Assessment of adaptive immune responses of dairy cows with Burkholderia contaminans-induced mastitis

Burkholderia contaminans, an emerging pathogen related to cystic fibrosis, is known to cause potentially fatal infections in humans and ruminants, especially in immunocompromised individuals. However, the immune responses in cows following its infection have not been fully elucidated. In this study, T- and B-lymphocytes-mediated immune responses were evaluated in 15 B. contaminans-induced mastitis cows and 15 healthy cows with multi-parameter flow cytometry. The results showed that infection with B. contaminans was associated with a significant decrease in the number and percentage of B lymphocytes but with a significant increase in the proportion of IgG(+)CD27(+) B lymphocytes. This indicated that humoral immune response may not be adequate to fight intracellular infection, which could contribute to the persistent bacterial infection. In addition, B. contaminans infection induced significant increase of γδ T cells and double positive (DP) CD4(+)CD8(+) T cells but not CD4(+) or CD8(+) (single positive) T cells in blood. Phenotypic analysis showed that the percentages of activated WC1(+) γδ T cells in peripheral blood were increased in the B. contaminans infected cows. Interestingly, intracellular cytokine staining showed that cattle naturally infected with B. contaminans exhibited multifunctional TNF-α(+)IFN-γ(+)IL-2(+)B. contaminans-specific DP T cells. Our results, for the first time, revealed a potential role of IgG(+)CD27(+) B cells, CD4(+)CD8(+) T cells and WC1(+) γδ T cells in the defense of B. contaminans-induced mastitis in cows.