Terminology and methodology

Cell surface proteins are denoted according to their cluster differentiation (CD) number. These are allocated after international workshops define individual cell surface proteins by reactivity to monoclonal antibodies. Most cells will express many such proteins and pattern of expression allows cellular characterisation.

Monoclonal antibodies (MoAbs) are derived from single B-lymphocyte cell lines and have identical antigen binding domains known as idiotypes. It is easy to generate large quantities of MoAbs for diagnostic use.

• Cell populations from e.g. PB or BM samples are incubated with a panel of MoAbs e.g. anti-CD4, anti-CD34 which are directly or indirectly bound to a fluorescent marker antibody e.g. FITC.

• Sample is passed through a fluorescence-activated cell sorter (FACS) machine.

• FACS instruments assign cells to a graphical plot by virtue of cell size and granularity detected as forward and side light scatter by the laser.

• Allows subpopulations of cells e.g. mononuclear cells in blood sample to be selected.

• The reactivity of this cell subpopulation to the MoAb panel can then be determined by fluorescence for each MoAb.

• A typical result for a CD4 T-lymphocyte population is shown: CD3, CD4 +ve; CD8, CD13, CD34, CD19 -ve.

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