IDO has a selective and potential role for Th2 differentiation and is regulated positively during antigenic presentation and the union of CTLA-4/B7·1/B7·2 in lymphocytes and dendritic cells; in response to infection and circulation nucleic acid through TLR4 and TLR9 activation; and by tissue inflammation [44] and they are critical regulator of adaptive immunity contributing to inflammatory process. Here, CTLA4 is linked to infection.