CD200 and immunoglobulin G4-related sclerosing disease: Further analysis of transcriptomes showed that other CTL-related genes, such as GPR56 and FAS ligand, were also upregulated in GC-type Tfh cells in the SMG lesions of IgG4-RD, whereas the expression levels of Tfh-related genes, such as IL-21, CD200, and Pou2af1 (also named as Bob1), in GC-type Tfh cells of IgG4-RD appeared to be relatively lower than those of GC-type Tfh cells in tonsils (Figure 1C).