Identification of rATG-binding targets by competitive inhibition of binding. NCI-H929 myeloma cells were incubated with control rabbit IgG (□) or rATG (▪) for 1 hour at 37°C followed by incubation on ice with the monoclonal antibody noted to assess for blockade of rATG binding. Myeloma cell lines and naive and CD40L-activated B cells were used as targets based on expression of the antigen of interest: RPMI-866 (IgG1, CD38), NCI-H929 (HLA-ABC, CD16, CD32, CD64, CD126 [IL-6R]), naive human B cells (CD52), CD40L-activated B cells (HLA-DR, CD19, CD20, CD27, CD30, CD40, CD80, CD95), and human myeloma cells (CD38, CD138). Significant inhibition of rATG binding to numerous B-cell-specific surface proteins from all stages of B-cell development was observed. Error bars denote 1 SD. The table shows the average fraction of myeloma cell lines and cells from 3 patients expressing the noted surface marker. Relative level of common expression of each marker among all cell types is summarized at the bottom of the table.