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Immune Function Panel by Flow Cytometry

The introduction of flow cytometry has allowed subclassification of lymphocytes on the basis of their immune function. Analysis of surface marker CD antigens can reveal imbalances or deficiencies in the various lymphocyte populations that make up the immune system. Acquired or congenital immunodeficiencies involving B cells include severe combined immunodeficiency, the bare lymphocyte syndrome, congenital hypogammaglobulinemia, common variable immunodeficiency, and IgA deficiency. T cell deficiencies include: DiGeorge syndrome, Wiskott Aldrich syndrome, and the acquired immunodeficiency syndrome.

The most frequent findings in the congenital immunodeficiency disorders are:

Severe combined immunodeficiency: Three different categories exist: (1) No mature T cells present, (2) no mature T cells present, but CD38 positive lymphocytes (immature thymocytes) in peripheral blood, (3) T cells co-expressing CD3, CD4, CD8, and CD38 (cortical thymocytes) are present in peripheral blood.

Bare lymphocyte syndrome: Normal absolute numbers of T and B cells, but almost all T cells are CD 8 positive. B cells have large amounts of surface IgM and IgD, like cord blood.

Congenital hypogammaglobulinemia: The hallmark is an absence of circulating B cells. T cells are normal or increased, with a normal CD4/CD8 ratio. Bone marrow contains increased numbers of pre-B cells.

Common variable immunodeficiency: Decreased serum immunoglobulin levels with normal numbers of T and B cells. B cells have immature or activated phenotypes.

IgA deficiency: Normal T and B cell phenotypes. IgA positive B cells coexpress IgM and IgD, indicating maturation arrest.

Congenital thymic aplasia (DiGeorge syndrome): Decreased numbers of mature (CD 3 positive) T cells. CD 8 positive T cells may be most affected, giving an increased CD4/CD8 ratio.

Wiskott Aldrich syndrome: may have decreased numbers of T and B cells. The deficiency becomes more pronounced with age. CD4/CD8 ratio can be increased, normal, or decreased.

Reference ranges are:

Specimen requirement is one 5 mL green top (sodium heparin) tube and one 5 mL lavender top (EDTA) tube of blood. Samples should remain at room temperature and transported to the laboratory within 24 hours of phlebotomy.