Test Details: Immunohistochemical testing helps to identify specific antigens (proteins) within tissue sections utilizing an antigen-specific antibody. CD21 is a receptor for Epstein barr virus, but it is not necessarily positive in EBV+ tumours. CD21 is positive in follicular dendritic cell tumours, hairy cell leukaemia, mantle cell lymphoma, marginal zone lymphoma, hyaline vascular variant of castleman disease, splenic littoral cell angioma and some T-ALL.