In addition to examining inflammatory cells, we evaluated the vascular integrity of the lung following SARS-CoV MA15 infection in the presence and absence of C3. We observed no differences in the numbers of platelets present in the bronchoalveolar lavage (BAL) fluid between C57BL/6J and C3–/– mice at either 2 or 4 days postinfection, indicating that the absence of C3 does not appear to significantly alter vascular permeability following infection with SARS-CoV (Fig. S2B). The gene discussed is C3; the disease is infection.