Test

immunophenotypic diagnosis of CLL

Background

CLL is a neoplasm of B-lymphocytes, but with a distinctive biology. Two key points are very relevant to diagnosis:

• First, the cells are "anergic" i.e. they have down-regulated their B-cell receptor (BCR) and its associated molecules - so immunoglobulin light chains, CD19, CD20 and particularly CD79b are all weakly expresssed.
• Second, the cells generally express CD5 and CD23 which are normally expressed on only a small proporton of normal B-cells

Consequently tyical CLL can be diagnosed with some confidence using flow cytometry, although atypical cases are regularly encoutered and pose more difficulty.

file CD45CLL.jpg left 250px

This image shows a typical CD45 ssc plot of CLL. Note that although the CLL cells (shown in blue) generally lie close to the position of normal lymphocytes, consistent with their anergic natures they will generally have lower expression of CD45 than normal typical T cells (shown in red) or NK cells (shown in green). They also have wider range of CD45 expression causing them to have a "sausage like" shape. This is a fairly typical appearance of CLL though not in itself diagnostic.

'Diagnosis of CLL

• CD19 should be detected but intensity is generally low in CLL
• CD5 should be expressed at moderate intensity in CLL (note also on expressed on mcl and occasionally on other lpd)
• CD23 has expected expression in CLL often at low intensity, generally absent in mcl but variably present on other lpd
• CD79b similar to CD19 this marker is expected to be expressed but intensity is generally low in CLL
• immunoglobulin light chains sig expect either light chain restriction with low intensity or undetectable
• fmc7 a marker of b-cell activation that should have low or absent expression, high expression is particularly seen in pll and hairy cell-like disorders
• CD200 expressed on most CLL cases as well as other b-lpd but is most frequently absent in mcl optional markers extended panel for atypical cases
• CD20 a pan b-cell marker with expected expression in CLL but intensity is generally low
• CD43 a pan b-cell marker with expected expression in CLL; frequently but not always absent in mcl