MRC1 and bacterial infectious disease: CD206 is a marker of anti-inflammatory activated macrophages in humans.1,36 Gene expression of CD206 by AMs in both control and SEA horses was increasedafter natural hay challenge.50 In contrast, the current study identified increased postchallenge expressionof CD206 only within the SEA group, which might indicate that the alveolar milieu inthe acute stage of SEA exacerbation drives AMs to a different phenotype than wouldoccur in bacterial infection.