Characterization of age-related changes in bovine CD8 ⁺ T-cells

Evaluation of the changes induced by immunological interventions requires a baseline against which to compare those changes. The age-related changes in the CD8 ⁺ T-cell population of cattle were studied. The results indicate that CD8 ⁺ T-cells could be divided into γ/δ TCR1 ⁺ and γ/δ TCR1 ^- according to their expression of the γ/δ T-cell receptor. As a proportion, the CD8 ⁺ γ/δ TCR1 ⁺ population appears to increase with age. Within the CD8 ⁺γ/δ TCR1 ^- a population of cells expressing a profile of surface molecules previously associated with effector memory T cells (CD45RO ⁺, CD62L ^-, CD27 ^-, CD45RA ^- and CD28 ^-) increases with age. Furthermore, a parallel increase with age in the proportion of CD8 ⁺CD45RO ⁺ T cells that express the cytotoxic granule protein perforin was observed. In peripheral tissues, namely lungs, it was found that the majority of CD8 ⁺ T cells present expressed a phenotype indicative of previously primed T cells (high expression of CD45RO and perforin). In contrast, only a small population of memory CD8 ⁺ T cells was present in lymphoid tissue where most of the CD8 ⁺ T cells expressed a naïve phenotype. In conclusion, in cattle, like in human, CD8 ⁺ T cells that express a phenotype associated with antigen experience accumulate with age that may play a role in immunocompetence as the individual ages.