Strain-Dependent Airway Hyperresponsiveness and a Chromosome 7 Locus of Elevated Lymphocyte Numbers in Cystic Fibrosis Transmembrane Conductance Regulator-Deficient Mice

Abstract

We previously observed the lungs of naive BALB/cJ Cftrtm1UNC mice to have greater numbers of lymphocytes, by immunohistochemical staining, than did BALB wild type littermates or C57BL/6J Cftrtm1UNC mice. In the present study, we initially investigated whether this mutation in Cftr alters the adaptive immunity phenotype by measuring the lymphocyte populations in the lungs and spleens by FACS and by evaluating CD3-stimulated cytokine secretion, proliferation, and apoptosis responses. Next, we assessed a potential influence of this lymphocyte phenotype on lung function through airway resistance measures. Finally, we mapped the phenotype of pulmonary lymphocyte counts in BALB × C57BL/6J F2 Cftrtm1UNC mice and reviewed positional candidate genes. By FACS analysis, both the lungs and spleens of BALB Cftrtm1UNC mice had more CD3+ (both CD4+ and CD8+) cells than did littermates or C57BL/6J Cftrtm1UNC mice. Cftrtm1UNC and littermate mice of either strain did not differ in anti-CD3–stimulated apoptosis or proliferation levels. Lymphocytes from BALB Cftrtm1UNC mice produced more IL-4 and IL-5 and reduced levels of IFN-γ than did littermates, whereas lymphocytes from C57BL/6J Cftrtm1UNC mice demonstrated increased Il-17 secretion. BALB Cftrtm1UNC mice presented an enhanced airway hyperresponsiveness to methacholine challenge compared with littermates and C57BL/6J Cftrtm1UNC mice. A chromosome 7 locus was identified to be linked to lymphocyte numbers, and genetic evaluation of the interval suggests Itgal and Il4ra as candidate genes for this trait. We conclude that the pulmonary phenotype of BALB Cftrtm1UNC mice includes airway hyperresponsiveness and increased lymphocyte numbers, with the latter trait being influenced by a chromosome 7 locus.