IDO2 and influenza: Given the dichotomy between IDO2's critical role in mediating the autoreactive B cell response in the in vivo KRN model of autoimmune arthritis and the lack of effect on responses to in vitro stimuli, we used two well-characterized models to measure normal B cell responses in vivo, the PR8 influenza infection model (47) and (4-hydroxy-3-nitrophenyl) acetyl (NP) immunization model (48, 49).