CD79a

Summary

A pan B-cell marker with relatively high specificity for the identification of B-lineage. CD79a is expressed initially in cytoplasm of early B cells, before appearing on the membrane at the time heavy chains of immunoglobulin become expressed.

Other relevant information

CD79a expression is recognised on some AML and T-ALL cases so caution should be exercised particularly where other features are atypical. Like CD19, expression of CD79a is more often associated with aml that has t 8;21 translocation though less common

Normal expression and function

CD79a associates with CD79b and the immunoglobulin chains form part of the B-cell receptor (BCR). CD79a and CD79b each mediate intracellular signalling. However the two chains are expressed slightly differently in B cells - CD79a is a more lineage-specific marker than CD79b and expression is acquired at a very early stage of B-lymphocyte formation. CD79a is expressed initially in cytoplasm before appearing on the membrane of mature cells, persisting until plasma cell differentiation when it is progressively lost.

Diagnostic role

• CD79a is a reliable marker of B-lymphocyte lineage with low levels of aberrant expression; it is more specific for B-cell lineage than CD19 or CD20, although it may rarely be expressed on other cell lineages.
• in ALL expression of CD79a is acquired in the cytoplam at an early stage of B-lineage commitment making it useful for identification of more primitive cases of ALL
• Expression is then retained on the cell surface through at later differentiation uuntil plasma cell differentiation where about half of cases of myeloma expressing CD79A strongly and a further proportion have weak expression.

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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
5-20%*	<5%	80-100%**	80-100%	5-20%***	<5%	20-40%	80-100%

Notes: * expression is more frequent in t(8;21) mutation, ** cytoplasmic expression is more frequent in early forms with surface expression acquired during maturation, *** expression in T-ALL is infrequent but recognised

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

Notes: * expression in myleoma is variable but frequently observed

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

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