Fig. 1.

The CD8 T cell response following acute RSV infection. (A) Following antigen presentation by DCs, naive CD8 T cells become activated, as measured by the upregulation of activation markers, such as CD11a, and the downregulation of the lymphoid homing receptor CD62L. Activated RSV-specific CD8 T cells expand both in frequency and total number in the lung, peaking at approximately 8–10 days following RSV infection. The peak of pulmonary CD8 T cell expansion coincides with complete viral clearance from the lung. (B) After peak expansion, contraction occurs to reduce the total number of RSV-specific CD8 T cells and form a stable memory population. (C) Based on their phenotype and circulatory properties, three primary memory CD8 T cell populations are formed following infection: T_CM, T_EM, and T_RM. T_CM (CD62L^hiCCR7^hiIL-7Rα^hiKLRG1^lo) primarily circulate between the blood and secondary lymphoid organs, while T_EM (CD62L^loCCR7^loIL-7Rα^loKLRG1^hi) predominate within the lung but are also capable of circulating within the blood. In contrast, T_RM (CD62L^loCD69^hiCD103^hi) represent a non-circulating, lung-resident population of memory CD8 T cells.