Though the percentages of gated lymphocyte populations (T or B cells) are important, it is still necessary to determine if the cells present have a normal or abnormal CD marker representation. A population will also need to be scrutinized to evaluate percentages of B and T lymphocytes.
Remember that lymphocytes will either be T cells or B cells and mature T cells will either be helper cells or cytotoxic cells. With this in mind, normal mature T cells should express CD2, CD3, CD5, CD7, and either CD4 or CD8.
- CD4 marks T-helper cells
- CD8 marks cytotoxic T cells
The CD markers present in the peripheral blood sample in Case Two are:
- CD2 = 17%
- CD5 = 97%
- CD7 = 17%
- CD3 = 18%
Note the markedly increased CD5 percentage in relation to the other T cell markers. If this were a normal T cell population, it would have CD5 of approximately 17%.
In order to determine if the elevated CD5 percentage is due to abnormal T cells or to abnormal B cells that are marking with CD5, the sample was stained with both CD5 and CD19 monoclonal antibodies. Two areas of interest are the cells positive for CD5 only and whether or not there is a CD19+/CD5+ dual marking population.
Note that on the image shown on the right, CD5+ only cells are 16.5% (rounds to 17%) indicating a normal T cell population in this sample.
T-cell analysis conclusion: T-cells are normal and the CD5+ cells that are also positive for CD19 represent abnormal B cells that express the T-cell marker, CD5.