BDNF and idiopathic pulmonary fibrosis: The rationale for investigating the TRP receptors in IPF is clear as there is evidence for the physiological up-regulation of this pathway; IPF patients have a greater cough reflex sensitivity to inhaled capsaicin [7, 8], and elevated levels of the neurotrophins NGF and BDNF in induced sputum and BAL fluid [5, 8], which are involved in neuronal differentiation and proliferation.