<qa>  What is the cytometric bead assay?Sputum and serum samples are analyzed by quantitative real-time polymerase chain reaction PCR qRT-PCR and by cytometric bead assay CBA. Components of the innate immune system mannose-binding protein, TLR recognition proteins and surfactant proteins are genetically determined from sputum or blood respectively. In the conduct of this study the investigators will retrospectively and systematically evaluate the available high-resolution computed tomography HRCT studies of affected patients 