CCL2 and severe acute respiratory syndrome: In agreement with the observed host gene response, expression of both inflammatory and anti-inflammatory mediators such as IL-1ra, IL-12, IL-13 and MCP-1 was upregulated in the lungs of infected animals on day 1 p.i. Upregulation of these genes was previously observed in serum and peripheral blood mononuclear cells in human cases of SARS [40], [41], [42].