[5] B cells express CR2 on their surfaces, allowing the complement system to play a role in B-cell activation and maturation.

A transcript with an open reading frame of 4,224 nucleotides encodes the long isoform, CR1; this is predicted to be a protein of 1,408 amino acids that includes 21 short consensus repeats (SCR) of ca.

[12] Although CR2 is present on all mature B-cells and follicular dendritic cells (FDCs), this becomes readily apparent only when immunohistochemistry is performed on frozen sections.

This feature can be useful in examining tissue where the normal germinal centres have been effaced by disease processes, such as HIV infection.

Castleman's disease is typified by the presence of abnormal FDCs, and both this, and malignant FDC tumours may therefore be demonstrated using CR2/CD21 antibodies.