Anti–IFN-γ autoantibody titers in relation to treatment with rituximab. (A) IFN-γ labeled beads were incubated with subject plasma at 10-fold serial dilutions to generate an Ab titration curve, as a function of fluorescence intensity, and determine a common dilution factor within the dynamic range of the assay. A representative example of the titration curve for patient 4 during rituximab therapy with the 1:5000 dilution indicated (black arrow) that lies within the linear phase of the dilution curve. (B) Each patient's Ab titer over the course of rituximab therapy was plotted at 1:5000 dilution.