CD4 and cystic fibrosis: Patients with cystic fibrosis (CF) complicated by allergic bronchopulmonary aspergillosis (ABPA) are vitamin D deficient and in vitro treatment with 1,25 (OH)2 vitamin D3 of CD4+ cells from CF patients with ABPA decreases Aspergillus fumigatus(Af)-induced Th2 responses.