Dendritic cell: T-cell interactions in spondyloarthritis.

The discovery of the association between spondyloarthritis (SpA) and HLA-B27 inevitably turned the spotlight on T-lymphocytes as the cells which recognize peptide antigens within the binding groove of the HLA-B27 molecule and then carry out effector functions. These include cytolysis, cytokine and chemokine production and activation of other effector cells, such as those which could destroy joints or drive new bone formation. In this view the T-cell assumed the role of "director" of the immune response and therefore, in inflammatory diseases such as SpA, of immuno-pathology. The important research questions under this paradigm were the identity of the peptides recognized by T-cells in disease, including whether they were derived from self proteins or from micro-organisms, the influence of HLA-B27 in selecting antigenic peptides for recognition by T-cells, the T-cell receptors used in recognition and the effector programmes which the T-cells initiated. Whilst these questions continue to be explored-many have not yet been answered-attention has shifted to a new "master regulator" of the immune response, namely the dendritic cell and the possibility that the genetic influences which contribute to susceptibility to SpA do so at the level of the dendritic cell (DC).