Immunoglobulin light chains

Summary

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.

Where cells express predomnantly kappa or lambda (light chain restriction) then clonality can be inferred.

Normal expression and function

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).

Diagnostic role

• 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.
• 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).
• Disease type: 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.

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SUMMARY TABLES

Note The colour and % refer to the proportion of cases expressing the marker. Additional comments on strength, or site of expression (if relevant) are given below the table. For full details of key click here. For further information about a particular disease state click <I> adjacent to the condition name

Expression in primitive cell types
AML	CMML	B ALL	BL	T ALL	ETP ALL	MPAL	Hgn
<5%	<5%	5-20%	80-100%*	<5%	<5%	5-20%	5-20%**

Notes: * Expression in ALL is not unique to Burkitt lymphome but strongly suggests this diagnoaia, ** surface light chains are expressed by mature haematogones

Expression in mature B cell neoplasms
CLL	MCL	FL	MZL	HCL	DLBCL	LPL	PCL
40-80%	80-100%	40-80%	80-100%	80-100%	40-80%	80-100%	<5%

Notes: All mature B cell malignancies will be clonally restricted; however in some disroders - most notably CLL, FL and DLBCL the expression may be too low to reliably detect by flow cytometry

Expression in mature T cell neoplasms*
ATLL	CTCL/Sezary	T-PLL	T-LGL	NK-LGL
<5%	<5%	<5%	<5%	<5%

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