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Revision as of 16:37, 28 May 2023

FMC7

The FMC7 antibody recognises an epitope of CD20 that has a more restricted pattern of expression than the parent molecule. FMC7 has high expression on late-stage b-cell neoplasms such as hairy-cell leukaemia or MZL and can be used to indicate their possible presence; however low level of FMC7 expression is frequent on other B-cell disorders so care is required in interpretation.

What is its normal function and expression

The identity of the FMC7 antigen was unclear for many years before being identified as an epitope of the CD20 molecule. FMC7 never received a CD classification number and retains the initials of the laboratory where it was raised: the Flinder Medical Centre. The particular function of FMC7 is not known, but like the CD20 molecule the FMC7 antigen is expressed by normal B-lymphocytes from the late pre-B-cell stage of development until their terminal differentiation and so is effectively a pan b-cell antigen that is particularly associated with late B cells that have features of activation.

What is its diagnostic role

FMC7 is widely expressed in B-NHL particularly where there is strong CD20 expression.
CD20 tends to have low expression on CLL but higher expression on other B-cell types particularly HCL, MCL and MZL
FMC7 therefore is most often used as an alert to draw attention to such disorders

Summary tables

1. expression by acute leukaemias and by haematogones rare pro-b all rare early pre-b all rare pre-b all hi b-all rare pro-t all rare mature-t all rare aml poss haemato-gones

2. expression by b-lymphoproliferative disorders

poss cll * hi pll** hi mcl freq fl hi hcl** hi hclv ** hi mzl hi lpl poss pcs

@@ Line 1: / Line 1: @@
-:Immunoglobulin light chains are part of the B-cell receptor and can therefore be considered as a pan B-cell marker - expressed from late lymphoblast stage until plasma cell differentiation.
+FMC7
-:If cells express predomnantly kappa or lambda (light chain restriction) then clonality can be inferred.
+The FMC7 antibody recognises an epitope of CD20 that has a more restricted pattern of expression than the parent molecule. FMC7 has high expression on late-stage b-cell neoplasms such as hairy-cell leukaemia or MZL and can be used to indicate their possible presence; however low level of FMC7 expression is frequent on other B-cell disorders so care is required in interpretation.
-normal function and expression
+What is its normal function and expression
-The immunoglobulin molecule (with either kappa or lambda light chain) forms the antigen-recognising portion of the B-cell receptor. Normal mature B cells therefore express light chains which are formed during pro-B to pre-B cell development appearing at the surface and remaining expressed on the cell surface until plasma cell development (when the immunoglobulin molecules become internal contaned within cytoplasmic secretory vesicles).
+The identity of the FMC7 antigen was unclear for many years before being identified as an epitope of the CD20 molecule. FMC7 never received a CD classification number and retains the initials of the laboratory where it was raised: the  Flinder  Medical  Centre. The particular function of FMC7 is not known, but like the CD20 molecule the FMC7 antigen is expressed by normal B-lymphocytes from the late pre-B-cell stage of development until their terminal differentiation and so is effectively a pan b-cell antigen that is particularly associated with late B cells that have features of activation.
+What is its diagnostic role
-what is its diagnostic role
+*FMC7 is widely expressed in B-NHL particularly where there is strong CD20 expression.
+*CD20 tends to have low expression on CLL but higher expression on other B-cell types particularly HCL, MCL and MZL
-*Indication of stage: acquisition of surface light-chain expression does not occur until a late point in B-precursor cell development so is useful be used to indicate developmental stage in ALL. Similarly, surface expression is lost at the point of plasma cell differentiation so absence od surface expression can indicate plasma cell developmental stage.
+*FMC7 therefore is most often used as an alert to draw attention to such disorders
-*Indication of clonality: malignant b-cells arise from a single parent cell so express light chain of a single type (either kappa or lambda) - light chain restriction. In many cases some normal cells will also be present so light chains may be a mixture of kappa and lambda. However when there is a malignant clone, cells expressing either kappa or lambda will predominate. Studies most frequently suggest that if the kappa to lambda ratio is greater than 3 1 then the presence of a clonal population can be inferred (although correlation with other markers is needed).
-*Weak or absent light chain expression may be seen in DLBCL FL or CLL and more rarely in MCL or MZL: overall around 10% of B-lymphoproliferative disorders do not express surface light chain.
+Summary tables
+. expression by acute leukaemias and by haematogones
+rare  pro-b all
+rare  early pre-b all
+rare  pre-b all
+hi  b-all
+rare  pro-t all
+rare  mature-t all
+rare  aml
+poss  haemato-gones
-summary tables
+. expression by b-lymphoproliferative disorders
-. expression by acute leukaemias and by
+poss
-rare pro-b all
+cll *
-poss  early pre-b all
+hi  pll**
-poss  pre-b all
+hi  mcl
-hi  b all
+freq  fl
-rare  pro-t all
-rare  mature-t all
-rare  aml
-poss  haemato-gones
-*  expressed by late haematogones
-. expression by b-lymphoproliferative disorders
-hi cll
-hi  pll**
-hi  mcl
-hi  fl
 hi  hcl**
-hi  hclv  l
+hi  hclv **
 hi  mzl
 hi  lpl
 poss  pcs

Extra: Difference between revisions

From haematologyetc.co.uk

Revision as of 16:37, 28 May 2023