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Diverse roles of B cells in the pathophysiology of rheumatoid arthritis are now well established. B cells contribute to autoimmunity by producing autoantibodies, processing autoantigen and the production of different cytokines which are involved in the inflammatory cascade. Therefore approaches to target B lymphocytes directly or indirectly are developed for clinical practice to treat autoimmune diseases including rheumatoid arthritis. Transient B cell depletion by rituximab (anti-CD20 antibody) has gained prime importance in recent years. Meanwhile anti-CD20 mediated transient B cell depletion therapy is now used with clinical efficiency in the treatment of patients with rheumatoid arthritis. Rituximab induces noteworthy changes in the homeostasis of peripheral B cell subpopulations during the repletion phase with emerging immature B cells in peripheral blood followed by normalization of the naïve B cell pool and a longterm delay in memory B cell subsets in patients with rheumatoid arthritis. Particularly IgD+CD27+ memory B cells repopulate very slowly during B cell regeneration. In a prospective clinical study, our laboratory has shown that the overall number of memory B cells correlates well to the duration of clinical response to rituximab. Little is known about the particular molecular changes in the memory B cell repertoire after rituximab therapy. To better understand peripheral memory B cell subsets, we explored in detail the somatic mutational frequency and pattern of Ig-VH3 gene rearrangements by using a single B cell sorting technique followed by nested PCR before and up to 6 years after rituximab therapy in 18 RA patients. We compared rituximab inflicted dynamics of mutational acquisition to memory B cell repopulation in 4 healthy donors and 6 non RA patients undergoing high dose chemotherapy followed by autologous or allogeneic stem cell transplantation (SCT). Firstly we analyzed the peripheral composition of memory B cell subsets. The phenotypic analysis of peripheral pre-switch (IgD+CD27+) and post-switch (IgD-CD27+) memory B cells did not reveal any quantitative differences in RA patients prior to B cell depletion therapy compared to healthy donors. However extending those studies in directly analysing the B cell immunoglobulin receptor from individual B cells of RA patients and healthy controls brought interesting results. Pre-switched and post-switched memory B cells showed a highly significant difference in the amount of mutations/sequence. The population of IgD+CD27+ memory B cells is comprised of non-mutated, low and highly mutated (median= 9 mutations/ sequence) rearranged Ig receptors whereas the IgD-CD27+ memory B cell compartment shows quite uniformly highly mutated (median 18 mutations/ sequence) sequences indicating a significant difference between these two groups (mutational frequencies 3.83±0.19% vs. 7.1±0.53%; P=0.0001). Profound changes were noted in the re-emerging pre-switch memory B cells (IgD+/ CD27+) after transient B cell depletion with rituximab. These cells showed over a time period of 6 years after treatment with rituximab significantly delayed acquisition of mutations in Ig receptors on the single B cell level. One year after a single course of rituximab 84% of single repopulating IgD+/CD27+ B cells were unmutated and no highly mutated Ig-VH gene rearrangements were found(P=0.0001). Over time increasing numbers of mutations could be detected i-e 7.8% during 2nd year of regeneration (P=0.0001), 14% after 4 years (n=2). Nevertheless even 6 years after rituximab, VH mutations in IgD+ memory B cells were still reduced with 27% highly mutated sequences compared to 52% pre therapy(P=0.0001). Post-therapy analysis of CDR3 length of regenerated IgD+ memory B cells revealed increased CDR3 length which also correlates well with elevated number of non-mutated VH gene rearrangements observed during repletion phase. In comparison patients undergoing high dose chemotherapy followed by allogeneic stem cell transplantation repopulated IgD+ memory cells earlier with higher numbers of mutations in IgD+ memory B cells. One year after transplantation Ig receptors showed already 22% highly mutated and 42 % unmutated VH rearrangements. These findings indicated that anti-CD20 mediated B cell depletion seems not only to delay the production of pre-switch memory B cells but also significantly affects the acquisition of mutations in the IgD+ memory B cell pool. In contrary to the mutational pattern of IgD+ memory B cells after rituximab class switched memory B cells repopulate in the periphery with quantitatively normal mutations in their Ig receptors. Although the numeric replenishment of these recirculating class-switched memory B cells was also reduced after rituximab, we found no delay in quantitative acquisition of mutations also an increased proportion of IgA expressing B cells in this memory B cell subset was detected. Our data showed that post-therapy mutational targeting in RGYW/WRCY motifs were significantly increased as compared with that of pre-treatment (27% before rituximab vs. 43% after therapy, P=0.0003) indicating that affinity maturation may operate differently in class-switched memory B cells before and after B cell depletion. These results indicate a normal development process with an unimpaired mechanism of mutational acquisition in class-switched memory B cells. These data argue for different requirements to undergo somatic hypermutations in IgD+ memory B cells in comparison to class switched memory B cells. To conclude, our work has demonstrated for the first time a delayed acquisition of somatic hypermutations at single Ig receptor VH gene rearrangements of IgD+ memory B cells in comparison to class-switched memory B cells. These results demonstrate that IgD+ memory B cells are particularly susceptible to anti-CD20 treatment in patients with rheumatoid arthritis. In addition antigenic pressure and/or selection are substantially reduced by rituximab therapy which is basically not seen in the class-switched memory compartment. These data are in line with the hypothesis that IgD+ memory B cells have distinct requirements for activating their mutational machinery compared to class-switched memory B cells which recover normal mutations during regeneration phase. The results have implications in understanding the pathophysiology of memory B cell in rheumatoid arthritis and may be helpful in designing new targeted therapies.
Von 1989 bis 2000 wurden an der Orthopädischen Universitätsklinik in Würzburg, König-Ludwig-Haus, 16 Patienten mit rheumatoider Arthritis aufgrund einer Vorfußdeformität mit Großzehengrundgelenksarthrodese und Resektion der II.-V. Metatarsophalangealgelenke operiert. 9 Patienten (11 Füße) konnten klinisch, radiologisch und pedographisch nachuntersucht werden (Gruppe A). Das Durchschnittsalter lag zum Zeitpunkt der Operation bei 58,1 Jahren. Der Nachuntersuchungszeitraum betrug im Durchschnitt 5,3 Jahre. Zum Vergleich wurden 12 Patienten (18 Füße), die von 1986 bis 1994 an der Großzehe mit Resektionsarthroplastik operiert wurden, nachuntersucht (Gruppe B). Das Alter während der Operation betrug durchschnittlich 53,3 Jahre. Die Nachuntersuchung erfolgte im Durchschnitt 10,7 Jahre später. Der Hallux-valgus-Winkel konnte in Gruppe A auf durchschnittlich 23°, in Gruppe B auf 34° korrigiert werden. Nach dem Score nach Kitaoka erreichte die Gruppe A durchschnittllich eine Punktzahl von 67, die Gruppe B 47 Punkte. Die geringe Punktzahl in Gruppe B wurde durch erneute Fehlstellung der Großzehe (67% dorsale Luxation, 50% H.-valgus-Rezidiv), Schwielen und metatarsalgische Beschwerden hervorgerufen. In Gruppe A traten in 2 Fällen schwerwiegende Komplikationen auf, die aber nicht direkt die Großzehe betrafen. Wundheilungsstörungen kamen in Gruppe A häufiger vor als in Gruppe B. Alle Arthrodesen waren knöchern konsolidiert. Die Patientenzufriedenheit betrug in Gruppe A 91%, in Gruppe B 83%. Bei der Pedographie zeigte sich in Gruppe A ein besseres Abrollverhalten über die Großzehe. In Gruppe B traten häufig abnormal hohe Druckwerte unter den Metatarsalen auf. Bei 85% korrelierte dies mit plantaren Schwielen. Dass das Interphalangealgelenk der Großzehe nach Arthrodese des Grundgelenks häufiger arthritische Veränderungen aufweist, konnte nicht bestätigt werden. Insgesamt ist die Großzehengrundgelenks-arthrodese als bevorzugte Operationsmethode anzusehen, da sie zur Stabilität des I. Strahls führt. Auch die Resektionsarthroplastik nach Hueter-Mayo ist aufgrund der hohen Patientenzufriedenheit empfehlenswert, führt jedoch im Langzeitverlauf zu einem deutlichen Korrektur- und Funktionsverlust.