CD20, or Cluster of Differentiate 20, is a protein that is generated on the surface of B-cells from the pre-B cell stage through fully developed B-cells in the periphery and bone marrow. Pro-B cells, normal plasma cells, and hematopoietic stem cells do not express CD20.

Lymphomas are malignancies of the lymphocytes, a kind of white blood cell. B-lymphocytes (B-cells) and T-lymphocytes (T-cells) are the two basic types of lymphocytes. Both kinds of lymphocytes aid in the defence of our bodies against infections.

B-cells and T-cells serve diverse purposes, and the tumours of each type of B-cell behave differently from the tumours of the other types of B-cells. Even with these distinctions, distinguishing the two below a microscope can be challenging. It is similar to a pair of twins who act and react differently to people on the inside but look similar on the outside.

CD20 is essentially a B-cell protein. Patients with some forms of leukaemia or B-cell lymphomas may have higher-than-normal levels of CD20. Employing a CD20 test to measure the quantity of CD20 on blood cells can aid in cancer diagnosis and treatment planning. CD20 test is also referred to as a tumour marker.

To elucidate, CD20, also known as B-lymphocyte antigen CD20, is an active glycosylated phosphoprotein that is present on the surface of all B-cells starting in the pro-B phase (CD117+, CD45R+) and gradually increases in proportion until maturity.

The MS4A1 gene encodes CD20 in humans. This gene encodes the membrane-spanning 4A gene series. Members of this emerging protein family have structural similarities, exon/intron splice frontiers, and distinct expression patterns in haematological cells and non-lymphoid organs.

Furthermore, this gene codes for a B-lymphocyte surface component involved in B-cell growth and transformation into plasma cells. This family member is among a group of relatives who are located on 11q12. This gene's alternative splicing produces two transcript variants, each of which encodes the same protein.

A CD20 test is instrumental in the detection of D20 deficiency in people with humoral immunodeficiency. The CD20 flow cytometry assay should always be carried out at the time suggested by the doctor. Both CD19 and CD20 markers are used to confirm the complete paucity of B-cells in presumed primary humoral immunodeficiencies.

The most common applications of the CD20 flow cytometry assay are as follows:

• CD20 deficiency is assessed in patients with a probable CD20 deficiency or humoral immunodeficiency
• Using both CD19 and CD20 tests aids in confirming the total absence of B-cells in putative primary humoral immunodeficiencies
• Quantifying therapeutic B-cell depletion in any clinical setting, encompassing cancer, autoimmune disorders such as systemic lupus erythematosus, membranous glomerulonephritis, and rheumatoid arthritis, among others
• Treatment or mitigation of acute humoral rejection in positive crossmatch kidney transplant recipients
• The CD20 test is inadequate for determining whether B-cells exhibit the target molecule (CD20) in the context of commencing therapeutic monoclonal anti-CD20 antibody treatment (Ofatumumab, Tositumomab, and Rituximab) for any of the haematological malignancies, or in other clinical situations.