Respiratory Syncytial Virus (RSV) Infects CD4+ T Cells: Frequency of Circulating CD4+ RSV+ T Cells as a Marker of Disease Severity in Young Children

Background. Although human airway epithelial cells are the main target of respiratory syncytial virus (RSV), it also infects immune cells, such as macrophages and B cells. Whether T cells are permissive to RSV infection is unknown. We sought to analyze the permissiveness of CD4(+) T cells to RSV infection. Methods. CD4(+) and CD8(+) T cells from cord blood, healthy young children, and adults were challenged by RSV or cocultured with infected HEp-2 cells. Infection, phenotype, and cytokine production by T cells were analyzed by flow cytometry or enzyme-linked immunosorbent assay. Expression of RSV antigens by circulating CD4(+) T cells from infected children was analyzed by flow cytometry, and disease severity was defined by standard criteria. Results. CD4(+) and CD8(+) T cells were productively infected by RSV. Infection decreased interleukin 2 and interferon. production as well as the expression of CD25 and Ki-67 by activated CD4(+) T cells. Respiratory syncytial virus antigens were detected in circulating CD4(+) and CD8(+) T cells during severe RSV infection of young children. Interestingly, the frequency of CD4(+) RSV+ T cells positively correlated with disease severity. Conclusions. Respiratory syncytial virus infects CD4(+) and CD8(+) T cells and compromises T-cell function. The frequency of circulating CD4(+) RSV+ T cells might represent a novel marker of severe infection.