The role of APRIL - A proliferation inducing ligand - In autoimmune diseases and expectations from its targeting.

Autoimmunity occurs when an adaptive immune response is directed against a self-antigen. As such, autoimmune reactions associated with the production of autoantibodies are common. These autoantibodies may either be pathogenic by inducing the initial damage to self, or exacerbate the reaction secondarily to the initial damage. In both cases, the pathway(s) leading to exposure of the immune system to the self-antigen inducing the production of autoantibodies is largely unknown. The latter is largely complicating the setting of putative prophylactic treatments. As a consequence, one possible way to control these diseases is to eliminate the cells producing antibodies. We will see that this approach is not yet part of any treatment in autoimmunity. Indeed, all the currently available non-specific immunosuppressive treatments do not target directly quiescent antibody-producing plasma cells. However, treatments aimed at depleting precursors of plasma cells, mature B-lymphocytes and/or antigen-experienced B cells not yet fully differentiated into plasma cells, are emerging. Such strategies were recently proven to be highly successful in several autoimmune disorders by two independent ways. The first way is by induction of B-cell cytotoxicity with an antibody directed against the surface antigen CD20. The second way is by antagonism of a key B-cell survival factor, the B-cell activation factor from the TNF superfamily (BAFF). In the present review, we will focus on the current knowledge regarding the role of a molecule related to BAFF, a proliferation-inducing ligand (APRIL), in autoimmune diseases, which acts on antibody-producing plasma cells. We will discuss expectations deriving from APRIL targeting in autoimmune diseases.