Lymphocytes are divided into two categories, T and B cells, according to their primary function within the immune system. In the body, T and B cells work together to help provide protection against infections, oncogenic agents, and foreign tissue, and they play a vital role in regulating self-destruction or autoimmunity.
Most circulating lymphocytes are T cells with a lifespan of months to years. The lifespan of B cells is measured in days. B cells (antibody) are considered bursa or bone marrow dependent and are responsible for humoral immunity (in which antibodies are present in the serum). T cells (cellular) are thymus derived and are responsible for cellular immunity. T cells are further divided into helper T (CD3+, CD4+) cells and suppressor T (CD3+, CD8+) cells.
Evaluation of lymphocytes in the clinical laboratory is performed by quantitation of the lymphocytes and their subpopulations and by assessment of their functional activity. These laboratory analyses have become an essential component of the clinical assessment of two major disease states: lymphoproliferative states (e.g., leukemia, lymphoma), in which characterization of the malignant cell in terms of lineage and stage of differentiation provides valuable information to the oncologist to guide prognosis and appropriate therapy, and immunodeficient states (e.g., HIV infection, organ transplantation), in which the alterations in the immune system that occur secondary to infection are evaluated.
The method of lymphocyte quantitation and characterization is based on the detection of cell surface markers by very specific monoclonal antibodies. For cell surface immunophenotyping, flow cytometry has become the method of choice. Cell surface phenotyping is accomplished by reacting cells from an appropriate specimen with one or more labeled monoclonal antibodies and passing them through a flow cytometer, which counts the proportion of labeled cells.
Normal Findings for Adult Peripheral Blood by Flow Cytometry
T and B surface markers:
Total T cells (CD3+): 53%–88%
Helper T cells (CD3+, CD4+): 32%–61%
Suppressor T cells (CD3+, CD8+): 18%–42%
B cells (CD19+): 5%–20%
Natural killer (NK) cells (CD16+): 4%–32%
Absolute counts (based on pathologist’s interpretation):
Total lymphocytes: 660–4600/mm3 (0.6–4.6 × 109/L)
Total T cells (CD3+): 812–2318/mm3
Helper T cells (CD3+, CD4+): 589–1505/mm3
Suppressor T cells (CD3+, CD8+): 325–997/mm3
B cells (CD19+): 92–426/mm3
NK cells (CD16+): 78–602/mm3
Lymphocyte ratio:
Helper-to-suppressor T-cell ratio >1.0
Obtain 5 mL of whole blood in a lavender-topped tube (with EDTA). Label the specimen with the patient’s name, date and time of collection, and test(s) ordered.
Do not refrigerate or freeze the sample; it should remain at room temperature until testing is performed. Collect a separate 5-mL venous EDTA-anticoagulated blood sample for hematology at the same time. Because the interpretation of data is based on absolute values, it is imperative that a WBC count and differential count also be performed so that the appropriate data can be obtained.
Standard immunosuppressive drug therapy usually decreases lymphocyte totals.
Patients with an absolute helper T-lymphocyte count of less than 200/mm3 are at greatest risk for developing clinical AIDS.
Decreased T cells occur in congenital immunodeficiency diseases (e.g., DiGeorge syndrome, thymic hypoplasia).
Decreased T cells occur in kidney and heart transplant recipients receiving OKT-3, an immunomodulatory drug used to prevent rejection.
A marked increase in B cells occurs in lymphoproliferative disorders (e.g., chronic lymphocytic leukemia). In the typical case of chronic lymphocytic leukemia, the B cells would be positive for either kappa or lambda light chains (indicating monoclonality) and would express CD19 (a B-cell antigen).
Pretest Patient Care
Explain purpose and specimen collection procedure. A recent viral cold can cause a decrease in total T cells, as can medications such as corticosteroids. Nicotine and strenuous exercise have also been shown to decrease lymphocyte counts.
Follow guidelines in Chapter 1 for safe, effective, informed pretest care.
Posttest Patient Care
Review test results; report and record findings. Modify the nursing care plan as needed.
Counsel the patient regarding abnormal findings; explain the need for possible follow-up testing and treatment. Lymphocyte immunophenotyping is performed to monitor patients who are HIV positive and have begun medication treatment. Transplantation patients are also retested at regular intervals to assess the threat of organ rejection or host infection. Also, see Chapter 8 for discussion of CD4 and CD8 cells.
Follow guidelines in Chapter 1 for safe, effective, informed posttest care.