Finally, while skewing toward Th2 CD4 T cell gene expression and limited Th1 gene expression has previously been shown to be associated with exacerbation and bacterial colonization,24 the underlying mechanisms responsible for these phenotypes are not well understood and there remains a lack of specific investigation of potential alterations of the function of Th1 or CD8 T cell responses in CF. This evidence concerns the gene CD4 and cystic fibrosis.