A single blood sample was collected from mild cases, 1-3 days after the development of respiratory symptoms. As controls, blood samples from 20 apparently healthy individuals were collected. Sequential blood/lung aspirate samples (standardized tracheal aspirates) were collected from the critically ill patients. The first sample was collected within 3 days for 13 patients; while one each was collected on 4 and 8 (pregnant woman) days after the appearance of symptoms (Table 1 ). Blood and lung aspirates were transported to the lab within half an hour of collection. Lung aspirates obtained from severe cases were immediately aliquoted and frozen at 280uC. An aliquot was mixed in 1:3 proportions with the RNAlater and stored at 280uC for gene analysis. Hundred microlitre of the blood sample from every patient was processed immediately for TLR staining as described below. In parallel, blood samples were immediately processed for the isolation of Peripheral Blood Mononuclear Cells (PBMCs) by density gradient centrifugation using Ficoll-Hypaque (Sigma). Plasma layer was removed and stored at 280uC in aliquots; cell pellets were stored in 500 ml RNALater solution (Ambion) at 280uC.