Sorted By Test Name - Mayo Medical Laboratories

CD4RT
89504
H/S ratio: > or =1.0
*Shearer WT, Rosenblatt HM, Gelman RS, et al: Lymphocyte subsets in healthy children from birth
through 18 years of age: The Pediatric AIDS Clinical Trials Group P1009 study. J Allergy Clin Immunol
2003;112(5):973-980
Clinical References: 1. Mandy FF, Nicholson JK, McDougal JS, CDC: Guidelines for performing
single-platform absolute CD4+ T-cell determinations with CD45 gating for persons infected with human
immunodeficiency virus. CDC. MMWR Morb Mortal Wkly Rep 2003;52:1-13 2. US Department of
Health and Human Services: Recommendations for prophylaxis against Pneumocystis carinii pneumonia
for adults and adolescents infected with human immunodeficiency virus. MMWR Morb Mortal Wkly Rep
1994;43:1-21 3. Shearer WT, Rosenblatt HM, Gelman RS, et al: Lymphocyte subsets in healthy children
from birth through 18 years of age: The Pediatric AIDS Clinical Trials Group P1009 study. J Allergy Clin
Immunol 2003 November;112(5):973-980
CD4 T-Cell Recent Thymic Emigrants (RTE)
Clinical Information: Naive T-cells are generated in the thymus and exported to peripheral blood to
form the peripheral T-cell repertoire. The complement of recirculating naive T cells remains relatively
constant throughout life, despite constant antigenic stimulation and reduction of thymic output with age.
Recent thymic emigrants (RTEs) refer to those populations of naive T cells that have not diluted their
TREC levels (T-cell receptor excision circles) with cell division. Naive T cells are long-lived in the
periphery and this, combined with new production of RTEs from the thymus maintains the peripheral
T-cell repertoire. RTEs express high levels of TRECs and undergo expansion and survival in an
antigen-independent manner, but still maintain their preselected T-cell repertoire.(1) In the CD4 T-cell
compartment it has been shown that naive CD45RA+ T cells coexpressing CD31 had higher levels of
TRECs compared to T cells lacking CD31.(2) The higher levels of TREC indicate a more recent thymic
ontogeny where the TRECs are not diluted by peripheral cell division. It has been shown that
CD31+CD4+ T cells continue to possess high levels of TREC despite an age-related tenfold reduction
from neonatal to older age.(3) CD4 RTEs (CD31+CD4+CD45RA+) have longer telomeres and higher
telomerase activity, which, along with the increased TREC levels, suggest a population of T cells with
low replicative history.(3) The same study has also shown that CD31+ CD4+ T cells are an appropriate
cell population to follow to evaluate thymic reconstitution in lymphopenic children posthematopoietic
stem cell transplant (HSCT).(3) A Mayo study shows that the CD31 marker correlates with
TREC-enriched T cells across the spectrum of age and correlates with thymic recovery in adults after
autologous stem cell transplantation.(4) CD31+ CD4 RTEs have also been used to evaluate T-cell
homeostatic anomalies in patients with relapsing-remitting multiple sclerosis (RRMS).(5) For patients
with DiGeorge syndrome (DGS)--a cellular immunodeficiency associated with other congenital problems
including cardiac defects, facial dysmorphism, hypoparathyroidism, and secondary hypocalcemia, and
chromosome 22q11.2 deletion (in a significant proportion of patients)--measurement of thymic function
provides valuable information on the functional phenotype, ie, complete DGS (associated with thymic
aplasia) or partial DGS (generally well-preserved thymic function).Thymus transplants have been
performed in patients with complete DGS but are not required in partial DGS.
Useful For: Evaluating thymic reconstitution in patients following hematopoietic stem cell
transplantation, chemotherapy, biological or immunomodulatory therapy, and immunosuppression
Evaluating thymic recovery in HIV-positive patients on highly active antiretroviral therapy (HAART)
Evaluating thymic output in patients with DiGeorge syndrome or other cellular immunodeficiencies
Assessing the naive T-cell compartment in a variety of immunological contexts (autoimmunity, cancer,
immunodeficiency, and transplantation) Identification of thymic remnants post-thymectomy for malignant
thymoma or as an indicator of relapse of disease (malignant thymoma)
Interpretation: The absence or reduction of CD31+CD4 RTEs correlates with loss or reduced thymic
output and changes in the naive CD4 T-cell compartment. CD4 RTEs measured along with CD8 RTEs
and TREC (TREC/87959 T-Cell Receptor Excision Circles (TREC) Analysis for Immune Reconstitution)
provides a comprehensive assessment of thymopoiesis. To evaluate immune reconstitution or recovery of
thymopoiesis post-T-cell depletion due to HSCT, immunotherapy, or other clinical conditions, it is
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