BDNF and idiopathic interstitial pneumonia: Furthermore, a study investigating pulmonary neurotrophin expression in patients with idiopathic interstitial pneumonia found evidence of enhanced expression of neurotrophins in the lungs of patients with IPF compared to other interstitial lung diseases, with fibroblastic foci in particular showing intense immunostaining for brain-derived neurotrophic factor and its receptor TrkB [27].