Rituximab (RTX), an anti-CD20 monoclonal antibody, is highly effective in the treatment of several autoimmune diseases. The mechanism by which RTX treatment improves rheumatoid arthritis and antineutrophil cytoplasmic antibody-associated vasculitis is not easily related to B cell depletion alone. Prior studies have shown that RTX mediates a rapid stripping of CD20 and CD19 from the human B cell through a process known as trogocytosis. The aim of the present study was to investigate whether changes in B cell phenotype resulting from trogocytosis would diminish the ability of B cells to promote autoimmune disease.
Human peripheral blood mononuclear cells were cultured with RTX under conditions that permitted trogocytosis. Changes in B cell phenotype and cytokine production were measured in the basal state and under conditions of activation with interleukin-4 (IL-4)/anti-CD40. The effects of RTX were characterized in terms of a requirement for interaction with the Fcγ receptor (FcγR) and other Fc-dependent interactions.
Trogocytosis induced a marked loss of surface CD19, IgD, CD40, and B cell-activating factor receptor, but did not alter induction of CD86 expression on purified B cells following IL-4/anti-CD40 treatment. Unexpectedly, RTX-dependent trogocytosis of normal human B cells in vitro led to a rapid up-regulation of IL-6 production, with no effect on the production of tumor necrosis factor α, IL-1β, interferon-γ, or IL-10. This effect was Fc-dependent and required the presence of an FcγR-bearing cell. Moreover, this effect involved the release of preformed intracellular IL-6 protein, as well as marked increases in IL-6 messenger RNA levels.
RTX-mediated trogocytosis of B cells in vitro results in acute production and release of IL-6. The nature of this effect and how it is related to the acute infusion reactions seen with RTX administration remain to be determined.