Charakterisierung der humoralen und zellulären Autoimmunantwort nach B-Zell-depletierender Therapie beim Pemphigus vulgaris

Pemphigus vulgaris (PV) is a severe, potentially life-threatening autoimmune disease, characterized by extensive blisters and erosions of skin and/or mucous membranes. IgG autoantibodies against the desmosomal adhesion proteins desmoglein (dsg) 3 +/- dsg1 have been shown to induce acantholysis of epidermal keratinocytes and subsequently blister formation. Although immunosuppressive medication is commonly applied, PV remains a therapeutical challenge. Adjuvant settings, such as immunoadsorption and more recently the monoclonal anti-CD20 antibody, rituximab, have been successfully introduced for the treatment of severe PV. Rituximab induces long-term clinical remission, which is probably due to depletion of autoreactive memory B cells as progenitors of autoantibody secreting plasma cells. Although PV is considered as an autoantibody mediated, organ specific autoimmune disease the induction and perpetuation of disease is thought to be controlled by dsg3-specific, autoreactive CD4+ T cells. In the present study, we investigated the impact of rituximab on frequencies of autoreactive dsg3-specific CD4+ T helper (Th) cells. Twelve PV patients with severe and/or recalcitrant disease, who received one cycle of rituximab combined with systemic immunosuppression, were included in the study. Over an observation period of twelve months on treatment we determined the frequencies of dsg3-specific Th1 and Th2 cells in peripheral blood of patients. After application of rituximab there was a significant decrease of dsg3-reactive CD4+ Th1 and Th2 cells. This decline was directly linked to complete depletion of peripheral B cells, which was detectable already one week after administration of rituximab and continued on average six to twelve months. There was a close correlation of frequencies of autoreactive Th1 and Th2 cells, respectively, and clinical course of PV, since we noticed a significant decline of peripheral dsg3-specific Th cells up to six months after rituximab therapy accompanied by complete remission in all investigated patients. In nine PV patients with ongoing clinical remission twelve months after therapy autoreactive Th cells remained decreased over the complete time, whereas three patients, relapsing twelve months after rituximab treatment, showed a reincrease of both dsg3-specific Th1 and Th2 cells at this time. Interestingly, the frequencies of peripheral CD3+, CD3+CD4+ and CD3+CD8+ T cells, respectively, remained unaffected by rituximab. Additionally, there was no reduction of peripheral tetanus toxoid-specific Th1 cells in rituximab-treated PV patients over the entire observation period. Summarizing the results, rituximab reveals a dual mode of action: i) depletion of CD20+ autoreactive B cells and, accordingly, depletion of progenitors of autoantibody secreting plasma cells, and ii) depletion of CD20+ autoreactive B cells functioning as antigen presenting cells resulting subsequently in a decrease of peripheral autoreactive CD4+ T cell numbers. Irrespective of the influence of rituximab on the cellular immune response, the monoclonal antibody has presumably a major impact on crucial factors for growth and survival of B cells. Therefore, we investigated the effect of rituximab on the B cell activating factors, BAFF (B cell activating factor of the TNF (tumor necrosis factor) family) and APRIL (a proliferation-inducing ligand), in the sera of 19 PV patients, who were divided into three groups depending on treatment options. The first group of patients was treated with immunosuppressive drugs alone, the second group received a combination of immunosuppression and immunoadsorption and the third group was treated with immunosuppression and adjuvant rituximab. Only in the group of rituximab-treated PV patients, we observed a pronounced and statistically significant induction of BAFF, correlating inversely with numbers of peripheral B cells. PV patients treated with immunosuppressive drugs alone or in combination with immunoadsorption did not show any significant alteration of serum BAFF levels. In contrast, APRIL levels were not significantly affected by each of the treatment schedules. Interestingly, there was a reduction of circulating, dsg3-specific autoantibodies in all patients, whereas titers of pathogen-specific Varicella Zoster Virus and Epstein Barr Virus IgG were significantly increased only in rituximab-treated patients. This induction of pathogen-specific antibodies was correlated to increasing concentrations of BAFF in serum of patients after B cell depletion. The results of the present study suggest a presumably differential effect of rituximab and subsequently BAFF on the induction of autoreactive versus pathogen-specific IgG antibody production.