CD27 and rheumatoid arthritis: To further map the phenotypic changes induced by smoking, we divided CD8+ T cells isolated from the peripheral blood of female RA patients and healthy controls into four populations based on the expression of CD107a, a degranulation marker expressed by cytotoxic cells releasing effector molecules, and CD27, a co-stimulatory receptor constituently expressed in naïve and memory cells (Figure 1A).