CD11c

Summary

An adhesion molecule whose expression is confined to leukocytes. High levels of expression are particularly useful in two ontexts:

Contributing to the identifyication of monocytic differentiation in myeloid disorders

Contributing to the idenfification hairy cell leukaemia or related disorders in lymphoid diagnosis, though care must be taken since expression is not fully specific to these disorders.

Normal expression and function

CD11c is an alpha chain of an integrin adhesion receptor that is best known as a complement receptor and for aiding monocyte and neutrophil adhesion to endothelium. CD11c is expressed predominantly by myeloid cells, at the highest density on monocytes and myeloid dendritic cells, but also at lower levels on granulocytes. In the lymphoid lineage it is expressed by NK cells and activated T or B lymphocytes.

Diagnostic role

• In the ymphoid lineage: Hairy cell leukaemia and marginal zone lymphomas tend to express CD11c strongly, although other B cell malignancies (including MCL and CLL) may express the antigen. Strong expression by lymphoid cells may indicate a possible hairy cell disorder.

In acute myeloid leukaemia cases with monocytic differentiation may express CD11c (approximately 50% of acute monoblastic leukaemias, acute monocytic leukaemias and acute myelo-monocytic leukaemias), but CD11c is not fully specific and is generally less helpful than CD14 as a monocyte marker.

Other relevant information:

CD11c is expressed at certain points in basophil and mast cell maturation and the pathological mast cells of systemic mastocytosis may express CD11c.'

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SUMMARY TABLES

Expression in primitive cell types
AML	CMML	B ALL	BL	T ALL	ETP ALL	MPAL	Hgn
20-40%	20-40%	<5%	<5%	<5%	<5%	5-20%	20-40%

Notes: CD11c can be a helpful indicator of monocytic lineage in AML or contribute to the identification of monocytic differentiation in MPAL. Expression occurs on late development haematogones

Expression in mature B cell neoplasms
CLL	MCL	FL	MZL	HCL	DLBCL	LPL	PCL
20-40%	20-40%	<5%	40-80%	80-100% strg	40-80%	40-80%	<5%

Notes: Strong expression is an expected finding in HCL, but note that this marker has a quite wide expression in LPD at lower expression

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

Notes: Although there have been few studies, CD11c expression does not appear to have value in the diagnosis of T cell disorders

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