Clearance of an Influenza A Virus by CD4+ T Cells Is Inefficient in the Absence of B Cells

The primary CD8⁺ T-cell response protected most B-cell-deficient μMT mice against intranasal infection with the HKx31 influenza A virus. Prior exposure did not prevent reinfection upon homologous challenge, and the recall CD8⁺ T-cell response cleared the virus from the lung within 7 days. Depleting the CD8⁺ T cells substantially reduced the capacity of these primed mice to deal with the infection, in spite of evidence for established CD4⁺ T-cell memory. Thus, the control of this relatively mild influenza virus by both primary and secondary CD4⁺ T-cell responses is relatively inefficient in the absence of B cells and CD8⁺ T cells.