CD4 and infection: The measurement of antibodies and T cells specific for P.aeruginosa and H.influenzae in patients with BR [31, 32] and COPD [30, 33] has previously revealed increased antibody responses associated with repeated infection, but decreased T cell responses, despite CD4+ T cell presence and oligoclonal TcR T cell expansion in the lungs [34, 35], suggesting immune dysregulation such as T cell exhaustion.