CD55 and neoplasm: When the expression levels of CD20 and CD55 on the surfaces of tumor cells were analyzed by FACS using anti-CD20 IgG antibody (rituximab) and anti-CD55 IgG antibody (4-1H)36, we found that CD20 expression was significantly lower in Ramos-RR cells (MFIRamos, CD20 = 413.5; MFIRamos-RR, CD20 = 278.0).