T- and B-lymphocyte assays are used to diagnose a number of immunologic disorders (Tables 3-1 and 3-2). A variety of methods are used. The most common way to assess T-cell activity is to measure the individual's response to delayed hypersensitivity skin tests. This involves intradermal injection of minute amounts of several antigens to which the individual has previously been sensitized (e.g., tuberculin, mumps, Candida). Erythema and induration should occur at the site within 24 to 48 hours. Absence of response is termed anergy and, thus, the test is frequently called an anergy panel. Anergy to skin tests reflects either a temporary or a permanent failure of cell-mediated immunity.¹⁰

Other measures of T and B lymphocytes involve determination of the number of cell types present. T lymphocytes are recognized by their ability to form rosettes with sheep erythrocytes (i.e., the sheep red cells surround the T lymphocyte). Although the sheep erythrocytes adhere to the cell membranes of the T lymphocytes, they react to neither B lymphocytes nor null cells.¹¹

T lymphocytes and their subsets also can be distinguished by their ability to react with various monoclonal antibodies. Monoclonal antibodies constitute a single species of immunoglobulins with specificity for a single antigen and are produced by immunizing mice with specific antigens. The most commonly used monoclonal antibodies to T lymphocytes are designated T3, T4, and T8. T3 is a pan-T-cell antibody that reacts with a determinant that is present on all mature peripheral T lymphocytes and can, therefore, be used to enumerate the total number of T cells present. T4 antibodies identify helper T cells, and T8 antibodies identify suppressor T cells.¹²

Other monoclonal antibodies include T10, T9, and T6. T10 and T9 antibodies react with very immature T lymphocytes (thymocytes) that are found in the thymus gland but not in the peripheral circulation. T10 antigen also is seen in mature thymocytes that are localized primarily in the medullary regions of the thymus. T6 antibodies also react with certain immature thymocytes. As T lymphocytes mature, reactivity to T6 antibodies is lost. Tests involving reactivity to immature T lymphocytes are useful in diagnosing T-cell leukemias and lymphomas.¹³

B lymphocytes are detected by immunofluorescent techniques. Such techniques involve mixing lymphocyte suspensions with heterologous antisera to immunoglobulins that have been labeled with a dye such as fluorescein. The antisera combine with B lymphocytes and when the suspension is examined by fluorescent microscopy, only B lymphocytes appear.¹⁴

T and B lymphocytes can be differentiated by electron microscopy, because T cells are smooth and B cells have surface projections. This technique is not, however, available in many laboratories.

* A decreased lymphocyte count (lymphopenia) usually indicates a decrease in the number of circulating T lymphocytes.

• Diagnosis of disorders associated with abnormal levels of T and B lymphocytes (see Table 3-1)
• Diagnosis of disorders associated with abnormal T-cell subtypes (see Table 3-2)
• Support for diagnosing acquired immunodeficiency syndrome (AIDS), as indicated by decreased helper T cells, normal or increased suppressor T cells, and a decreased ratio of helper to suppressor T cells
• Diagnosis of severe combined immunodeficiency disease (SCID), an inherited disorder characterized by failure of the stem cell to differentiate into T and B lymphocytes (Fig. 3—3)
• Diagnosis of Di George's syndrome, characterized by failure of the thymus (and parathyroids) to develop, with a resulting decrease in T lymphocytes (see Fig. 3—3)
• Diagnosis of X-linked agammaglobulinemia, characterized by severe B-lymphocyte deficiency (see Fig. 3—3)
• Diagnosis of common variable hypogammaglobulinemia (CVH), characterized by absent, decreased, or defective B cells and most commonly caused by either lack of helper T lymphocytes or abnormal suppressor T cells (see Fig. 3—3)

Nursing Care Before the Procedure

Client preparation is the same as that for any study involving the collection of a peripheral blood sample (see Appendix I).

A venipuncture is performed and the sample collected in a green-topped tube or other type of blood collection tube, depending on laboratory preference.

Nursing Care After the Procedure

Care and assessment after the procedure are the same as for any study involving the collection of a peripheral blood sample.

• Because the client may be immunosuppressed, assess the site for signs of infection.
• Complications and precautions for compromised immune status: Note and report helper T-cell level and relation to suppressor T-cell level or decreased B cells. Administer chemotherapy or other ordered medications. Provide reverse protective precautions to prevent infection.