T-And B-Lymphocyte Assays

Lymphocytes - key cells in the immune system - have the capacity to recognize antigens through special receptors found on their surfaces.

Cell separation is used to isolate lymphocytes nom other cellular blood elements. This procedure recovers about 80% of the lymphocytes but doesn't differentiate between T cells and B cells. The percentage of T cells and B cells is determined by attaching a label or marker and using different identification techniques.

Null cells possess Fc receptors but no other detectable surface markers and have no diagnostic significance. The number of null cells is usually determined by subtracting the sum of T cells and B cells nom totallymphocytes.

Purpose

• To aid diagnosis of primary and secondary immunodeficiency diseases
• To distinguish benign nom malignant lymphocytic proliferative diseases
• To monitor response to therapy

Patient preparation

• Explain to the patient that this test measures certain white blood cells.
• Tell him that the test requires a blood sample and who will perform the venipuncture and when.
• Reassure him that although he may experience transient discomfort from the needle puncture and the pressure of the tourniquet, collecting the sample takes less than 3 minutes.

Procedure and posttest care

• Perform a venipuncture, and collect the sample in a 7-ml green-top tube.
• Because many patients with T-cell and B-cell changes have a compromised immune system, keep the venipuncture site clean and dry.
• If a hematoma develops at the venipuncture site, apply warm soaks.

Precautions

• Completely fill the collection tube, and invert it gently several times to adequately mix the sample and anticoagulant.
• Send the sample to the laboratory immediately to ensure viable lymphocytes.
• If antilymphocyte antibodies are suspected, as in autoimmune disease, notify the laboratory.

Reference values

T-cell and B-cell assays are being standardized, and values may differ from one laboratory to another, depending on test technique.

• Percentage of total lymphocytes:
  - T cells: 53% to 88%
  - B cells: 5% to 20%.
• Total lymphocyte count: 1,500 to 3,000/µl
• T-cell count: 812 to 2,3 I 8 cells/µl
• B-cell count: 99 to 426 cells/µl

These counts are higher in children.

Normal T-cell and B-cell counts don't necessarily ensure a competent immune system. In autoimmune diseases, such as systemic lupus erythematosus and rheumatoid arthritis.

T cells and B cells, although present in normal numbers, may not be functionally competent.

Abnormal findings

An abnormal T-cell or B-cell count suggests but doesn't confirm specific diseases. The B-cell count is elevated in chronic lymphocytic leukemia, multiple myeloma, Waldenstrom's macroglobulinemia, and DiGeorge's syndrome.

B cells decrease in acute lymphocytic leukemia and in certain congenital or acquired immunoglobulin deficiency diseases. In other immunoglobulin deficiency diseases, especially if only one immunoglobulin class is deficient, the B-cell count remains normal.

The T-cell count rises occasionally in infectious mononucleosis; it rises more often in multiple myeloma and acute lymphocytic leukemia.

The T-cell count decreases in congenital T-cell deficiency diseases, such as DiGeorge's, Nezelof's, and Wiskott-Aldrich syndromes, and in certain B­cell proliferative disorders, such as chronic lymphocytic leukemia, Waldenstrom's macroglobulinemia, and acquired immunodeficiency syndrome.

Interfering factors

• Failure to use the proper collection tube
• Failure to adequately mix the sample and the anticoagulant
• Failure to send the sample to the laboratory immediately
• Changes in health status, such as nom stress, surgery, chemotherapy, steroid or immunosuppressive therapy, or X-rays (possible rapid change in T- and B-cell counts)
• Immunoglobulins, such as autologous antilymphocyte antibodies that sometimes occur in autoimmune disease (possible change in results)