Lymphocyte Subsets

Distinct lymphocyte subsets including T-cells, B-cells, and natural killer (NK) cells are identifiable by characteristic cell surface marker molecules. T-cells are involved in cell mediated immunity, B-cells with humoural immunity and NK cells play a role in defence against viral infections and tumours. T-cells are CD3 positive, B-cells are CD19 positive, and NK cells are CD3 negative, CD16 and CD56 positive. T-cells are further classified as helper cells (CD4 positive,) or cytotoxic cells (CD8 positive,). In turn, CD4+ and CD8+ cells can be classified as naïve (CD4RA+, CD8RA+) or memory cells (CD4RO+, CD8RO+).

The absolute number and percentage of different lymphocyte subsets can vary in various diseases. For example, in individuals with human immunodeficiency virus (HIV) infection, the number of CD4+ cells and the CD4+: CD8+ ratio is affected by the stage of disease and response to treatment. Thus, lymphocyte subset analysis can provide information regarding the immune status of the HIV infected patient and assist in monitoring therapy. Characteristic lymphocyte subset profile can be seen in a number of primary immunodeficiency disorders. A specific test request for T-cell subsets only test for CD4 and CD8 lymphocytes and is used for monitoring anti-retroviral treatment and HIV infection.