IgH sequence analysis of 3 GC-LCLs lacking surface immunoglobulin expression.IgH sequences (corresponding to codons 9-94) of the surface immunoglobulin-negative GC-LCLs A5, A28, and B53 aligned to the corresponding most homologous germline sequence. The IgH sequence of the A5 cell line contains a 7-nt insertion (shaded) downstream of CDR2; A28 sequence has stop codons (boxed) introduced within CDR1 and CDR2, and B53 sequence has stop codon (boxed) introduced in CDR1.