Utility: 1) Comprehensive initial screening for cellular and humoral inherited immune deficiency.
             2) Leukocyte adhesion deficiencies.
Specimen: 4 - 10 mL peripheral blood in sodium heparin (green top).
CPT codes: 86359, 86360, 86355, 86357, 88184, 88185 x 13, 88188.

Clinical indication/general description
Primary immunodeficiencies (PIDDs) and secondary immunodeficiencies present with recurrent upper and lower respiratory tract infections (encapsulated and atypical bacteria), deep-seated infections, recurrent or deep-seated abscesses, intractable diarrhea and failure to thrive. In addition, PIDDs also can present with autoimmune manifestations and malignancies. Evaluation of patients with these manifestations includes enumeration of the different types of lymphocytes (T cells, B cells and natural killer (NK) cells) because an absolute lymphocyte count from a complete blood count differential can miss important deficiencies in specific subsets of lymphocytes.

The PID2 assay is a more extensive enumeration of the different subsets of lymphocytes and also will identify patients with defects in the expression of adhesion molecules on neutrophils. Leukocyte adhesion deficiency Type I (LAD-I), also known as LFA-1 deficiency, is caused by a decreased expression of CD18 and LAD-II is caused by the decreased expression of CD15. Additionally, the PID2 assay also will detect the increased activation of CD4 T cells or CD8 T cells that may be caused by an ongoing viral infection or immune dysregulation. Activated human T cells express the HLA class II protein (CD4+DR+ or CD8+DR+) and an isoform of the CD45 antigen known as CD45RO. Numerous immunodefi¬ciencies associated with decreased numbers of T cells, B cells or NK cells can be detected with this assay including
DiGeorge syndrome (low T cell numbers will be detected), AIDS (low CD4 cell counts will be detected), X-linked agammaglobulinemia (low B cells will be detected) and NK cell deficiencies (low NK cell numbers will be detected).

Detection methodology
The assay is designed to enumerate the percent and absolute cell counts of T helper cells (CD3+CD4+), T cytotoxic cells (CD3+CD8+), B cells (CD19+) and NK cells (CD3-CD16+/CD56+). The assay examines the expression of CD18 and CD15 on neutrophils, and enumerates the numbers of T cells that are activated (CD4+HLADR+ or CD8+HLADR+ cells and CD4+CD45RO+ cells). CD4+CD45RO+ cells also are referred to as "memory" T cells.

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