IL-10 is expressed by T helper 2 (Th2) cells, B cells, DCs, and macrophages (Moore et al., 2001), and also by Th1 cells (Anderson et al., 2007; Assenmacher et al., 1994; Del Prete et al., 1993; Gerosa et al., 1996; Jankovic et al., 2007; Pohl-Koppe et al., 1998) and (reviewed in O'Garra and Vieira, 2007; Trinchieri, 2007), certain regulatory (Treg) T cells (Moore et al., 2001; O'Garra and Vieira, 2004; Roncarolo et al., 2006), and Th17 cells (Awasthi et al., 2007; Fitzgerald et al., 2007; McGeachy et al., 2007; Stumhofer et al., 2007).