As higher M2 alveolar macrophage counts have been documented during allergic asthma (51), we tried to determine whether asthma-induced increased Brucella susceptibility could be the result of the preferential invasion of M2 macrophages by Brucella. Microscopic analysis showed a strong increase in the frequency of both iNOS+ and arginase-1+ cells in the lungs of Alt sensitized mice. Here, ARG1 is linked to allergic asthma.