Alpha Beta Double-Negative T Cells for Autoimmune Lymphoproliferative Syndrome

CPT CODE:

USEFUL FOR:

Diagnosing autoimmune lymphoproliferative syndrome (ALPS)

SPECIMEN REQUIRED:

Send specimen Monday through Thursday only.  Draw and package specimen as close to shipping time as possible. Ship specimen priority overnight.
Draw blood in a lavender-top (EDTA) tube(s), and send 3 mL of EDTA whole blood. Specimen cannot be frozen. Note:    1. Ordering physician name and phone number              are required on request form for processing. 2.  For serial monitoring, we recommend that    specimen draws be performed at the same time of    day.

TRANSPORT TEMPERATURE:

Ambient\Refrig OK\Frozen NO

CLINICAL INFORMATION:

Autoimmune lymphoproliferative syndrome (ALPS, also known as Canale-Smith syndrome) is a complex clinical disorder of dysregulated lymphocyte homeostasis that is characterized by lymphoproliferative disease, autoimmune cytopenias, splenomegaly, and lymphadenopathy with an increased susceptibility to malignancy.(1)
Genetic defects in the apoptosis pathway have been determined for most cases of ALPS. Apoptosis (programmed cell death) plays a role in normal immune homeostasis by limiting lymphocyte accumulation and autoimmune reactivity. The interaction of the surface receptor CD95 (FAS) and its ligand (CD95L;FASL) triggers the apoptotic pathway in lymphocytes.
The following molecular ALPS classification has been established:
ALPS ClassificationMolecular/Genetic Defect in ApoptosisType IaCD95 (FAS) mutations(1)Type IbHeterozygous CD95L (FASLG) mutations(1)Type IcHomozygous CD95L (FASLG) mutation(2)Type IICASP8 or CASP10 mutations(1,3)Type IIIUnknown(1,3)
Patients with ALPS have an increase in a normally rare population of T cells (typically <1%) that are alpha beta T-cell receptor (TCR)-positive, as well as negative for both CD4 and CD8 coreceptors (double-negative T cells: DNT).(1) The alpha beta TCR DNT cells from ALPS patients also express an unusual B-cell-specific CD45R isoform, called B220.(4,5) B220 expression on alpha beta TCR DNT cells has been demonstrated to be a sensitive and specific marker for ALPS and is associated with FAS mutations.(4)
Several other diseases can present with an ALPS-like phenotype, including independent conditions like Evans syndrome (a combination of autoimmune hemolytic anemia and autoimmune thrombocytopenic purpura), Rosai-Dorfman disease (massive painless cervical lymphadenopathy that may be accompanied by leukocytosis, elevated erythrocyte sedimentation rate [ESR], and hypergammaglobulinemia), and nodular lymphocyte-predominant Hodgkin disease.(1)
The absolute counts of lymphocyte subsets are known to be influenced by a variety of biological factors, including hormones, the environment,and temperature. The studies on diurnal (circadian) variation in lymphocyte counts have demonstrated progressive increase in CD4 T-cell count throughout the day, while CD8 T cells and CD19 B cells increase between 8:30 am and noon, with no change between noon and afternoon. Natural killer (NK) cell counts, on the other hand, are constant throughout the day.(6)Circadian variations in circulating T-cell co

CLINICAL INTERPRETATION:

The presence of increased circulating T cells (CD3 ) that are negative for CD4 and CD8 (double-negative T cells: DNT) and positive for the alpha/beta T-cell receptor (TCR) is required for the diagnosis of ALPS.
The laboratory finding of increased alpha beta TCR DNT cells is consistent with ALPS only with the appropriate clinical picture (nonmalignant lymphadenopathy, splenomegaly, and autoimmune cytopenias). Conversely, there are other immunological disorders, including common variable immunodeficiency (CVID), which have subsets for patients with this clinical picture, but no increase in alpha beta TCR DNT cells.
If either the percent of the absolute count of either the alpha beta TCR DNT cells or alpha beta TCR DNT B220 cells is abnormal, additional testing is indicated. All abnormal alpha beta TCR DNT cell results should be confirmed (for ALPS) with additional testing for defective in vitro lymphocyte apoptosis, followed by confirmatory genetic testing for FAS mutations (contact MLI for test forwarding information).

REFERENCE VALUES:

Alpha beta TCR DNT cells

                2-18 years: <2% CD3 T-cells

                19-70 years: <3% CD3 T-cells

Alpha beta TCR DNT cells

                2-18 years: <35 cells/uL

                19-70 years: <35 cells/uL

Alpha beta TCR DNT B220 cells

                2-18 years: <0.4% CD3 T-cells

                19-70 years: <0.3% CD3 T-cells

Alpha beta TCR DNT B220 cells

                2-18 years: <7 cells/uL

                19-70 years: <6 cells/uL