Potential explanation for increased SREBP in CF epithelial cells and decreased SREBP in AM macrophages that lack CFTR could be that intracellular cholesterol pools to the decreased mSREBP expression and decreased SRE activity seen in the AM with decreased CFTR expression, as Cav1 expression is negatively regulated by SRE in macrophages. Here, CFTR is linked to cystic fibrosis.