CD4 and CD8 T cells participate in the immune memory response against Vaccinia virus after a previous natural infection

The present study evaluates the immune response of memory CD4⁺ and CD8⁺ T cells from patients following a natural Vaccinia virus (VACV) infection. A total of 42 individuals were involved in the study being: 22 previously infected individuals (vaccinated or not against smallpox) and 20 non-infected individuals (vaccinated or not). A short-term in vitro stimulation with UV-inactivated VACV of whole blood cells was performed. Our study showed that previously infected individuals have a lower percentage of CD4⁺ T cells expressing lymph-node homing receptors (CD4⁺CD62L⁺CCR7⁺) and higher percentage of memory CD4⁺ T cells subsets (CD4⁺CD45RO^High) when compared with non-infected subjects, after in vitro viral stimulation. We also showed that infected individuals presented higher percentages of CD4⁺ and CD8⁺ memory T lymphocytes expressing IFN-γ when compared to non-infected individuals. We verified that the percentage of CD4⁺ and CD8⁺ T memory cells expressing TNF-α was higher in infected and non-infected vaccinated subjects when compared with non-infected unvaccinated individual. We also observed that previously infected individuals have higher percentages of CD8⁺ T cells expressing lymph-node homing receptors (CCR7⁺ and CD62L⁺) and that the memory T cells expressing IFN-γ and TNF-α were at higher percentages in the whole blood cells from infected and non-infected vaccinated individuals, when compared to unvaccinated non-infected subjects. Thus, our findings suggest that CD4⁺ and CD8⁺ T cells are involved in the immune memory response against Vaccinia virus natural infection.