Mechanisms of lymphocyte loss in SARS coronavirus infection.

1. Human lymphocytes and monocytes are not permissive to productive SARS coronavirus (SARS-CoV) infection in vitro. 2. Challenge of lymphocytes and monocytes with infectious SARS-CoV, inactivated virions, and receptor-binding fragment of spike protein does not trigger apoptosis. 3. Direct infection/interaction between viruses and lymphocytes/monocytes is unlikely to be the cause of lymphopaenia in SARS patients. 4. Lymphopaenia in SARS patients is likely to result from indirect mechanisms secondary to the viral infection.