In systemic lupus erythematosus all pathways lead to endogenous nucleic acids-mediated production of interferon α (IFNα).
Increased production of autoantigens during apoptosis (UV-related and/or spontaneous), decreased disposal, deregulated handling and
presentation are all important for the initiation of the autoimmune response. Nucleosomes containing endogenous danger ligands that
can bind to pathogen-associated molecular pattern receptors are incorporated in apoptotic blebs that promote the activation of DCs and
B cells and the production of IFN and autoaantibodies, respectively. Cell surface receptors such as the BCR and FcRIIa facilitate the
endocytosis of nucleic acid containing material or immune complexes and the binding to endosomal receptors of the innate immunity
such as TLRs. At the early stages of disease, when autoantibodies and immune complexes may not have been formed, antimicrobial
peptides released by damaged tissues such as LL37 and neutrophil extracellular traps, may bind with nucleic acids inhibiting their
degradation and thus facilitating their endocytosis and stimulation of TLR-7/9 in plasmacytoid DCs. Increased amounts of apoptosisrelated
endogenous nucleic acids stimulate the production of IFN and promote autoimmunity by breaking self-tolerance through
activation and promotion of maturation of conventional (myeloid) DCs. Immature DCs promote tolerance while activated mature DCs
promote autoreactivity. Production of autoantibodies by B cells in lupus is driven by the availability of endogenous antigens and is
largely dependent upon T cell help, mediated by cell surface interactions (CD40L/CD40) and cytokines (IL21). Chromatin-containing
immune complexes vigorously stimulate B cells due to combined BCR/TLR crosslinking. DC, dendritic cell, BCR, B cell receptor, FcR, Fc
receptor, UV, ultraviolet; TLR, toll-like receptor. Reprinted with permission from Bertsias GK, Salmon JE, Boumpas DT. Therapeutic
opportunities in systemic lupus erythematosus: state of the art and prospects for the new decade