AbstractObjectiveSpondylarthritis (SpA) is characterized by spinal and peripheral joint inflammation, frequently combined with extraarticular manifestations. Despite the well‐established association of SpA with the class I major histocompatibility complex (MHC) allele HLA–B27, there are still different, parallel hypotheses on the relationship between HLA–B27 and disease mechanisms. The present study was undertaken to investigate several characteristics of mature dendritic cells (DCs), which are believed to be essential for triggering disease in a model of SpA in HLA–B27–transgenic rats.MethodsWe combined different whole‐proteome approaches (2‐dimensional polyacrylamide gel electrophoresis and iTRAQ) to define the most aberrant molecular processes occurring in spleen DCs. Videomicroscopy and flow cytometry were used to confirm both cytoskeletal and class II MHC expression deficiencies.ResultsOur proteome studies provided evidence of up‐regulation of proteins involved in class I MHC loading, and unfolded protein response, along with a striking down‐regulation of several cytoskeleton‐reorganizing proteins. The latter result was corroborated by findings of deficient motility, altered morphology, and decreased immunologic synapse formation. Furthermore, class II MHC surface expression was reduced in DCs from B27‐transgenic rats, and this could be linked to differences in class II MHC–induced apoptotic sensitivity. Finally, we found reduced viability of the CD103+CD4− DC subpopulation, which likely exerts tolerogenic function.ConclusionTaken together, our findings have different important implications regarding the physiology of B27‐transgenic rat DCs, which have a putative role in spontaneous disease in these rats. In particular, the reduced motility and viability of putatively tolerogenic CD4+ DCs could play an important role in initiating the inflammatory process, resulting in SpA.