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CD22 expression is largely restricted to b cell lineage and expression is acquired at an early differentiation stage.

• expression varies during mature b-cell development however the major value of CD22 lies in the identification of all based on high lineage-specificity and very early acquisition allowing the identification of pro-b all.

normal expression and function CD22 is a membrane receptor that binds sialic acid containing glycans and expression is mostly restricted to b cells where it is believed to be a negative regulator of activation. expression is developmentally related - first appearing in cytoplasm then on the surface in pre-b cells CD22 is fully expressed by mature b cells but lost on plasma cell differentiation. basophils express CD22.

other relevant information as a result of its restricted expression CD22 has emerged as a therapeutic target in acute lymphoblastic leukemia all and other b cell disorders.

diagnostic role

• its early cytoplasmic expression gives CD22 particular value in the detection of pro b-all diagnosis requires expression of two of the following three markers CD22 membrane or cytoplasm ; CD19 or CD79a. CD22 may not be uniformly expressed across the population with expression being seen on 60-90 of cells.
• in mature b cell neoplasms CD22 has relatively low expression in cll mcl and fcl but has markedly increased expression in hcl and related disorders.

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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