Sorted By Test Name - Mayo Medical Laboratories

a more recent thymic ontogeny where the TRECs are not diluted by peripheral cell division. Healthy
infants and children maintain thymic T cell production levels. There is an age-related decline in this
thymic function, so that by adulthood the thymus contributes minimally, if at all, to the maintenance of
CD8 T cell levels. Therefore, measurement of CD8 RTE by itself, in adults, is of limited clinical value.
This decline in the production of CD103+CD62L+ CD8 RTE can also be precipitated by thymectomy or
loss of thymic function.(2) Additionally, these cells are quite short-lived in the periphery.(2,3) A Mayo
study shows that in adults over the age of 20 there is no linear correlation between CD8 RTE expressing
CD103 and CD62L (3) and TREC levels, suggesting that homeostasis in the CD8 T-cell compartment is
probably maintained more by peripheral expansion than thymic output. This concept may be corroborated
by the fact that CD8 T-cell counts recover numerically more rapidly posthematopoietic stem cell
transplant (HSCT) than do CD4 T cells, resulting in a skewed CD4:CD8 ratio for several months to 1-year
posttransplant, and that increase in CD4 T-cell counts coincides with associated thymic recovery.
Useful For: An indicator of thymic function in patients post-hematopoietic stem cell transplantation
(HSCT), chemotherapy, immunomodulatory therapy, and immunosuppression To perform a
comprehensive assessment of thymopoiesis, measurement of CD4 RTE (CD4RT/89504 CD4 T-Cell
Recent Thymic Emigrants [RTE] and TRECs (TREC/87959 T-Cell Receptor Excision Circles [TREC]
Analysis for Immune Reconstitution) should be performed in conjunction with this (CD8 RTE) test. Such
testing is particularly helpful in evaluating thymic function in pediatric patients (