The AP-1 transcription factor Batf3 is required for homeostatic development of CD8α+ classical dendritic cells that prime CD8 T-cell responses against intracellular pathogens. Here, we identify an alternative, Batf3-independent pathway for their development operating during infection with intracellular pathogens mediated by the cytokines IL-12 and IFN-γ. This alternative pathway results from molecular compensation for Batf3 provided by the related AP-1 factors Batf, which also functions in T and B cells, and Batf2 induced by cytokines in response to infection. Reciprocally, physiologic compensation between Batf and Batf3 also occurs in T cells for expression of IL-10 and CTLA-4. Compensation among BATF factors is based on the shared capacity of their leucine zipper domains to interact with non-AP-1 factors such as Irf4 and Irf8 to mediate cooperative gene activation. Conceivably, manipulating this alternative pathway of dendritic cell development could be of value in augmenting immune responses to vaccines.

Rheumatoid Arthritis (RA) is an autoimmune disorder characterized by T cell dysregulation. We have shown that an altered peptide ligand (A9) activates T cells to utilize an alternate signaling pathway which is dependent upon FcRγ and Syk, resulting in downregulation of inflammation. In the experiments described herein we have attempted to determine the molecular basis of this paradox. Three major SFKs found in T cells (Lck, Fyn, and Lyn) were tested for activation following stimulation by A9/I-Aq. Unexpectedly we found they are not required for T cell functions induced by A9/I-Aq, nor are they required for APL stimulation of cytokines. On the other hand, the induction of the second messenger inositol trisphosphate (IP3) and the mobilization of calcium are clearly triggered by the APL A9/I-Aq stimulation and are required for cytokine production albeit the cytokines induced are different from those produced after activation of the canonical pathway. DBA/1 mice doubly deficient in both IL-4 and IL-10 were used to confirm that these two cytokines are important for the APL-induced attenuation of arthritis. These studies provide a basis for exploring the effectiveness of analog peptides and the inhibitory T cells they induce as therapeutic tools for autoimmune arthritis.