SFTPA2 and idiopathic pulmonary fibrosis: The most studied biomarkers able to discriminate IPF from healthy donors are the markers Krebs von den Lungen (KL)-6 [80,81,82,83], the chitinase-like protein (YKL40) [84,85], leucocytes and circulating innate immune cells [78,79,80], and surfactant proteins (SP)-A, -B, -D [86,87,88,89,90,91].