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1.What is lymphoma?
Lymphomas are cancer that arises in lymphocytes. Lymphocytes are WBCs present in lymph nodes, thymus, spleen, bone marrow and specific lymphoid pockets all over the body. They are immune system cells that have varied functions right from fighting and preventing infections to the healing of infections and in autoimmunity. Lymphomas are of 2 types, viz. Hodgkin and Non-Hodgkin. In lymphomas, lymphocytes change, grow in an uncontrolled and uninhibited fashion, each category affects a different type of lymphoid cell, and they show variable responses to therapy.
2. What are the symptoms of lymphoma?
Symptoms of lymphoma are fever, chills, night sweats, unexplained weight loss, loss of appetite, painless swelling of lymph nodes in the neck, armpits or groin region, weakness, fatigue, shortness of breath, chest pain, coughing, swollen abdomen or bloating after small meals and itchy skin.
3. What is leukemia?
Leukemias are cancer of blood-forming cells inside the bone marrow. Blood cells are constituents of blood which includes red blood cells, white blood cells and platelets. Their precursors are present in the marrow in an immature form which undergoes maturation to get released into the blood.
4. Which type of LPD is more common?
Lymphocytes are of two types- B lymphocytes and T lymphocytes. In peripheral blood, 80-90% is T-cells. B lymphocytes constitute only a minority (10-20%) in circulating blood, but B-cell LPDs are more common as compared to their T-cell counterparts.
5. What is flow cytometry?
Flow cytometry is a highly specialized laboratory test done on a cytometer with the help of laser beam and fluorescent dyes or tagged substances (antibodies) to identify the types of cells in the blood, bone marrow or lymph node samples. It can also identify particular components within the cell and count a specific number of cells. Its most common use in medicine is immunophenotyping and diagnosis of leukemia and lymphomas.
6. What are the indications of doing flow cytometry assay?
Indications of doing flow cytometry in LPDs are as follows:
i. Significant lymphocytosis (>6 *109/L) – high lymphocyte counts
ii. Lymphadenopathy and lymphocytosis
iii. Abnormal lymphoid cell morphology on peripheral blood film or bone marrow
iv. Splenomegaly with or without cytopenias (either or all 3 cell lines are low) where LPDs are a possibility
v. Unexplained cytopenias where LPDs are a possibility
vi. Persistent unexplained erythroderma
vii. Presence of splenomegaly and lymphadenopathy but doing a lymph node biopsy is not possible
7. What does CD stand for?
CD stands for cluster of differentiation which is also known as cluster of designation or classification determinant. The pattern of surface CD antigen expression indicates the degree of maturity. It is a protocol utilized to identify and investigate molecules present on cell surfaces. This later helps in providing targets for immunophenotyping of cells and diagnosis of lymphomas and leukemia.
8. What are the normal functions of CD19?
Various functions of CD19 are:
a. B-cell antigen receptor (BCR) factor plays an important role in the maintenance and differentiation of mature B cells and CD19 is an essential co-factor for this activity. The decision of whether a particular cell will live, proliferate, activate, differentiate or die, during B-cell development, is tightly regulated via BCR interactions and signalling. CD19 functions to increase the pre-BCR/BCR signals and modulates the fate of B-cell during multiple stages of development.
b. CD19 forms a multimolecular complex with CD21, CD81 and CD225 on the surface membrane of mature B cells and acts as a dominant signalling component.
c. CD19 along with functional BCR also plays an important role in humoral immunity, pathogen-specific immunity by producing antibodies and the continued survival of the peripheral immune system. They identify soluble antigens or activated complement system products via immunoglobulins anchored on their surface and differentiate into plasma cells with secrete antibodies and immunoglobulins thereby providing immunity.
9. Does CD19 hold a special status in diagnosis?
Yes. CD19 is more sensitive than CD20 in detecting B cell acute leukemia. Also, excess of CD19 will further guide the clinician towards a definitive diagnosis of LPDs.
10. What is the role of CD19 in multiple myeloma?
Plasma cells are derived from B-lymphocytes. CD19 expression is observed in normal plasma cells. However, this test is, not useful in malignant plasma cells isolated from patients having developed multiple myeloma as myeloma cells lack CD19 expression. However, in early pre-myeloma stages, flowcytometry shows a mixture of both CD19 positive and negative cells.
11. What is the panel of testing for B cell LPDs?
When B cell LPDs are suspected, you need testing for CD19, CD20, CD79a, CD22, CD38, CD23, CD5, CD10, FMC7, HLA-DR, kappa and lambda. Mature B-cells express surface CD19, CD79a and usually CD20. Immature B-cells characteristically shows cytoplasmic CD19 with or without surface CD19 and CD79a, but are usually CD20 negative. The gold standard for identifying cells of B-cell lineage is cytoplasmic CD79a expression. Peripheral blood B-cells normally expresses CD22 and FMC7 with surface light chain expression of either kappa or lambda at a ratio of between 2:1 and 3:2.
12. How does this test help in lymphoma treatment?
If malignant lymphoma cells express CD19, specifically targeted immunotherapy can be given for treatment. In this way, CD19 testing and the recent availability of CD19 targeting specific treatment have revolutionized lymphoma therapy.
13. Can I directly ask for this testing if I have any symptoms?
No. It is always the treating physician’s call. After correlating with other lab parameters, symptoms and clinical findings, the decision of doing CD19 testing is taken based upon suspicion of LPDs.
care.phadkelabs@agilus.in
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