Lung, spleen and liver tissues were fixed with formalin, embedded in paraffin and sectioned. Then, the tissue sections were stained with H&E or Masson's-trichrome stain. The prevalence of lungs with hemorrhage was estimated and the score of the left lobe was calculated using H&E staining: 4, 75–100% 3, 50–75% 2, 25–50% 1, 0–25% and 0, no hemorrhage.23 (link) For the in situ TUNEL assay, cell death was determined using a TUNEL staining kit (Roche Diagnostics, Indianapolis, IN, USA).21 (link) Briefly, sections of paraffin-embedded lung tissues were deparaffinized and subjected to antigen retrieval. Then, the sections were incubated with a mixture of TdT and fluorescence-labeled nucleotides. The prepared sections were examined with Olympus BX51 microscope (Olympus, Tokyo, Japan) and Qimaging camera (RoHs, Surrey, British Columbia, Canada). For pulmonary immune complex deposition, the frozen sections were stained with FITC-conjugated anti-C3 and Alexa Fluor 647-conjugated anti-mouse IgG (Abcam, Cambridge, UK). DNA was visualized using DAPI (Sigma-Aldrich), and the sections were examined with Olympus BX51 microscope and Qimaging camera.