<p>In sera remitted for anti-nuclear antibody (ANA) analysis, the supplement of a sensitive anti-SSA/Ro ELISA to the conventional ANA screening by immunofluorescence (IF) revealed that one fourth of the individuals with IF-ANA negative, but SSA/Ro ELISA positive sera, had systemic lupus erythematosus (SLE) or cutaneous LE. Consequently, adding a sensitive anti-SSA/Ro ELISA to the ANA screening is valuable for the serological detection of ANA negative SLE/LE patients.</p><p>SLE patients often have measurable interferon-alpha (IFN-α) levels in serum, and IFN-α treatment of patients with non-autoimmune diseases can induce SLE. Thus, the type I IFN system seems to be important in SLE and was therefore investigated. Initially, a decreased IFN-α producing capacity, due to a 70-fold reduction in the number of circulating natural IFN-α producing cells (NIPC), was noted in peripheral blood mononuclear cells (PBMC) from SLE patients. SLE-sera contained an endogenous IFN-α inducing factor (SLE-IIF), consisting of IgG and DNA in the form of small immune complexes (300-1000 kD). The SLE-IIF selectively activated NIPC and was more common in sera from patients with active disease compared to individuals with inactive disease. IFN-α producing cells could be detected by immunohistochemistry in both lesional and unaffected skin from SLE patients, and IFN-α gene transcription could be verified by in situ hybridisation in some of the skin biopsies. A reduced number of NIPC, detected by expression of the blood dendritic cell antigen (BDCA)-2, was noted among SLE-PBMC. The IFN-α production triggered by SLE-IIF in SLE-PBMC was inhibited by monoclonal antibodies (mAbs) to BDCA-2 and markedly decreased by anti-BDCA-4 mAbs. </p><p>The observations in the present thesis may explain the ongoing IFN-α production in SLE patients, indicate an important role for the activated type I IFN system in the pathogenesis, and suggest that direct targeting of SLE-NIPC may constitute a new therapeutic principle in SLE.</p>

<p>Patients with systemic lupus erythematosus (SLE) have an activated type I interferon (IFN) system with an ongoing IFN-α synthesis. This may be caused by circulating immune complexes, consisting of anti-DNA antibodies (Abs) and DNA, with IFN-α inducing capacity. Produced IFN-α may be crucial in the pathogenesis, because this cytokine can break tolerance and promote autoimmunity.</p><p>In the present thesis, possible mechanisms of the IFN-α production in SLE were studied. To investigate whether IFN-α inducing material could be derived from apoptotic cells, IgG from SLE patients (SLE-IgG) were combined with apoptotic cells. This combination induced high IFN-α production in normal peripheral blood mononuclear cells (PBMC). The IFN-α induction was associated to presence of anti-RNP Abs, but not to anti-dsDNA Abs, indicating that two inducers could be active in SLE, one containing DNA and the other RNA.</p><p>Apoptotic cells and SLE-IgG exclusively activated the natural interferon producing cells (NIPC) and the IFN-α response was enhanced by type I IFN and inhibited by IL-10 and TNF-α. The IFN-α induction was dependent on FcγRII, because blocking this receptor reduced IFN-α production and NIPC were found to express FcγRIIa.</p><p>To further elucidate the role of different autoantibodies in the IFN-α induction, sera from patients with Sjögren´s syndrome (SS), containing autoantibodies to RNA binding proteins (SSA, SSB, RNP and/or Sm) were investigated. The combination of SS or SLE sera and apoptotic or necrotic cell material induced high IFN-α production in PBMC. RNA, but not DNA, was required for IFN-α induction, indicating that RNA and Abs to RNA-binding proteins form potent IFN-α inducing complexes.</p><p>The findings in this thesis can explain central mechanisms for the activation of NIPC in SLE, and perhaps also other autoimmune diseases. This activation is mediated by interferogenic immune complexes, and modulating the NIPC activation may be a novel therapeutic approach in SLE.</p>

In sera remitted for anti-nuclear antibody (ANA) analysis, the supplement of a sensitive anti-SSA/Ro ELISA to the conventional ANA screening by immunofluorescence (IF) revealed that one fourth of the individuals with IF-ANA negative, but SSA/Ro ELISA positive sera, had systemic lupus erythematosus (SLE) or cutaneous LE. Consequently, adding a sensitive anti-SSA/Ro ELISA to the ANA screening is valuable for the serological detection of ANA negative SLE/LE patients. SLE patients often have measurable interferon-alpha (IFN-α) levels in serum, and IFN-α treatment of patients with non-autoimmune diseases can induce SLE. Thus, the type I IFN system seems to be important in SLE and was therefore investigated. Initially, a decreased IFN-α producing capacity, due to a 70-fold reduction in the number of circulating natural IFN-α producing cells (NIPC), was noted in peripheral blood mononuclear cells (PBMC) from SLE patients. SLE-sera contained an endogenous IFN-α inducing factor (SLE-IIF), consisting of IgG and DNA in the form of small immune complexes (300-1000 kD). The SLE-IIF selectively activated NIPC and was more common in sera from patients with active disease compared to individuals with inactive disease. IFN-α producing cells could be detected by immunohistochemistry in both lesional and unaffected skin from SLE patients, and IFN-α gene transcription could be verified by in situ hybridisation in some of the skin biopsies. A reduced number of NIPC, detected by expression of the blood dendritic cell antigen (BDCA)-2, was noted among SLE-PBMC. The IFN-α production triggered by SLE-IIF in SLE-PBMC was inhibited by monoclonal antibodies (mAbs) to BDCA-2 and markedly decreased by anti-BDCA-4 mAbs. The observations in the present thesis may explain the ongoing IFN-α production in SLE patients, indicate an important role for the activated type I IFN system in the pathogenesis, and suggest that direct targeting of SLE-NIPC may constitute a new therapeutic principle in SLE.

Patients with systemic lupus erythematosus (SLE) have an activated type I interferon (IFN) system with an ongoing IFN-α synthesis. This may be caused by circulating immune complexes, consisting of anti-DNA antibodies (Abs) and DNA, with IFN-α inducing capacity. Produced IFN-α may be crucial in the pathogenesis, because this cytokine can break tolerance and promote autoimmunity. In the present thesis, possible mechanisms of the IFN-α production in SLE were studied. To investigate whether IFN-α inducing material could be derived from apoptotic cells, IgG from SLE patients (SLE-IgG) were combined with apoptotic cells. This combination induced high IFN-α production in normal peripheral blood mononuclear cells (PBMC). The IFN-α induction was associated to presence of anti-RNP Abs, but not to anti-dsDNA Abs, indicating that two inducers could be active in SLE, one containing DNA and the other RNA. Apoptotic cells and SLE-IgG exclusively activated the natural interferon producing cells (NIPC) and the IFN-α response was enhanced by type I IFN and inhibited by IL-10 and TNF-α. The IFN-α induction was dependent on FcγRII, because blocking this receptor reduced IFN-α production and NIPC were found to express FcγRIIa. To further elucidate the role of different autoantibodies in the IFN-α induction, sera from patients with Sjögren´s syndrome (SS), containing autoantibodies to RNA binding proteins (SSA, SSB, RNP and/or Sm) were investigated. The combination of SS or SLE sera and apoptotic or necrotic cell material induced high IFN-α production in PBMC. RNA, but not DNA, was required for IFN-α induction, indicating that RNA and Abs to RNA-binding proteins form potent IFN-α inducing complexes. The findings in this thesis can explain central mechanisms for the activation of NIPC in SLE, and perhaps also other autoimmune diseases. This activation is mediated by interferogenic immune complexes, and modulating the NIPC activation may be a novel therapeutic approach in SLE.