CD8+ T cell responses in bronchoalveolar lavage fluid and peripheral blood mononuclear cells of infants with severe primary respiratory syncytial virus infections

A protective role for CD8(+) T cells during viral infections is generally accepted, but little is known about how CD8(+) T cell responses develop during primary infections in infants, their efficacy, and how memory is established after viral clearance. We studied CD8(+) T cell responses in bronchoalveolar lavage (BAL) samples and blood of infants with a severe primary respiratory syncytial virus (RSV) infection. RSV-specific CD8(+) T cells with an activated effector cell phenotype: CD27(+)CD28(+)CD45RO(+)CCR7(-)CD38(+)HLA-DR(+)Granzyme B(+)CD127(-) could be identified in BAL and blood. A high proportion of these CD8(+) T cells proliferated and functionally responded upon in vitro stimulation with RSV Ag. Thus, despite the very young age of the patients, a robust systemic virus-specific CD8(+) T cell response was elicited against a localized respiratory infection. RSV-specific T cell numbers as well as the total number of activated effector type CD8(+) T cells peaked in blood around day 9-12 after the onset of primary symptoms, i.e., at the time of recovery. The lack of a correlation between RSV-specific T cell numbers and parameters of disease severity make a prominent role in immune pathology unlikely, in contrast the T cells might be involved in the recovery process.