To determine whether the cytotoxic ability of CD4 and CD8 T cell responses was altered in CF, we measured the intracellular expression of granzyme B (gzmB) and found no significant differences in the percentage of gzmB+ CD4 (Fig. 3A) or CD8 (Fig. 3B) T cells between non-CF and CF samples. This evidence concerns the gene CD4 and cystic fibrosis.