MPO and Autoimmunity: Having demonstrated dendritic cell TLR9 ligation is required for the generation of systemic anti-MPO autoimmunity, anti-MPO T cell recall responses and subsequent kidney injury and further demonstrating that TLR9 ligation upregulates dendritic cell CD40 expression (Figure 1), the importance of CD40-induced dendritic cell activation as a second signal for the induction of nephritogenic autoimmunity was further assessed.