Long before the advent of CD antibodies, the distinctive morphology of HCs was highly suggestive of the activated nature of the malignant cells. Subsequent studies have indeed shown the HCs express a number of antigens (e.g., FMC7, CD22, CD25, CD72, CD40L) associated with the activation of B cells and other cell types (Table 29.2),6but lack CD23, which is expressed by CLL cells and upregulated during normal B-cell activation.6 Moreover, certain HC-"restricted" antigens,
Table 29.2 Activation features
Upregulated activation antigens (e.g., FMC-7, CD22, CD25, CD72, CD40L)
Downregulation of antigens often reduced during activation of other cells types (e.g., CD21 and CD24)
HC-"restricted" antigens probably indicative of activation (e.g., CD11c, CD68, CD103, HC-2, cyclin D1 and TRAPa)
Surface microvilli and ruffles, relatively abundant basophilic cytoplasm, open nuclear chromatin aTRAP = tartrate-resistant acid phosphatase.
such as CD11c, CD68c, CD103, HC-2, cyclin D1, and TRAP, have also been associated with the activation of certain lymphoid and non-lymphoid cell types.7 Interestingly, both the CD21 and CD24 markers, normally lost after B-cell activation, are expressed by HCs only at low levels.6
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