Purification of GC cells and phenotype of GC-derived transformants. (A) Tonsillar B-cell suspensions were stained with PE-Cy5-labeled anti-CD10 mAb, and CD10⁺ GC cells were positively selected by FACS sorting. Percentages of CD10⁺ cells in the unsorted and enriched populations are indicated; note that such CD10⁺ cells lack CD23 expression¹³  (left panels). The resultant GC-derived LCLs were stained with PE-Cy5-labeled anti-CD10 and FITC-labeled anti-CD23 mAbs; CD10 and CD23 expression (open profiles) are shown relative to isotype control values (shaded profiles) for 2 surface immunoglobulin-negative GC-LCLs, A9 and A28 (right panels); all GC-LCLs examined, irrespective of surface immunoglobulin status, were CD10^-CD23⁺. (B) Immunoglobulin isotype expression in GC-LCLs was analyzed by 2-color flow cytometry after staining with the following combinations of isotype-specific antibodies: RPE-labeled anti-IgM and FITC-labeled anti-IgA, RPE-labeled anti-IgG and FITC-labeled anti-IgD, and RPE-labeled anti-λ and FITC-labeled anti-κ (Dako). The A26 (IgG⁺, λ⁺) and B21 (IgM⁺, IgD⁺, κ⁺) GC-LCLs served as positive controls, and A9 and A28 were representative surface immunoglobulin-negative GC-LCLs. Note that A9 and A28 were also negative for surface IgE and for the CD79b component of the surface immunoglobulin complex (data not shown). (C) EBV latent antigen expression in the 6 surface immunoglobulin-negative LCLs (A5, A9, A27, A28, B10, B53) was analyzed by immunoblotting protein extracts of these lines with mAbs to EBNA1, EBNA2, LMP1, and LMP2. Included as controls are 2 surface immunoglobulin-positive GC-LCLs from the same experiment (A26, B21), the EBV-negative B-lymphoma line BJAB and the EBV-transformed cord blood LCL X50-7.