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CD22 expression is largely restricted to B-lymphocytes

Expression varies during mature b-cell development, however the major value of CD22 lies in the identification of ALL

This value is based on high lineage-specificity and very early acquisition in cytoplasm then cell surface

normal expression and function

CD22 is a membrane adhesion receptor whose expression is mostly restricted to B lymphocytes where it is believed to be a negative regulator of activation. Expression is developmentally related - first appearing in cytoplasm of pro-B cells then on the surface in pre-B cells. CD22 is fully expressed by mature-B cells, but is lost during plasma cell differentiation. Basophils express CD22.

other relevant information The restricted expression of CD22 makes it a potential therapeutic target in B cell disorders

diagnostic role

• Cytoplasmic expression of CD22 gives particular value in the detection of pro-B ALL where diagnosis requires expression at least two of: CD22 (membrane or cytoplasm), CD19 or CD79a. CD22 may not be uniformly expressed across a cell population with expression often being seen on only 60-90 of cells
• in mature B cell neoplasms CD22 has relatively low expression in CLL, MCL and FL, but has high expression in HCL

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1. expression by acute leukaemias and by haematogones file freqepng pro-b all link flow cytometry key file hiepng early pre-b all link flow cytometry key file hiepng pre-b all link flow cytometry key file hiepng early b all link flow cytometry key file rareepng pro-t all link flow cytometry key file rareepng mature-t all link flow cytometry key file rareepng aml link flow cytometry key file hiepng haemato-gones link flow cytometry key *basophils are recognised to express CD22

2. expression by b-lymphoproliferative disorders file hiepng frame cll * link flow cytometry key file hiepng pll** link flow cytometry key file hiepng mcl link flow cytometry key file hiepng fl * link flow cytometry key file hiepng hcl** link flow cytometry key file hiepng hclv link flow cytometry key file hiepng mzl link flow cytometry key file hiepng lpl link flow cytometry key file possepng pcs link flow cytometry key * typically weak ** typically strong