||T cells are critical components of the adaptive immune system and have been implicated in many pathologic conditions including autoimmune disease, cancer and immunodeficiency. Peripheral T-cells are divided into na´ve, memory, effector, and regulatory subsets based on their proliferation capabilities, cytokine/transcription factor expression profile, and surface marker expression patterns. Newly generated T-cells released from the thymus, termed recent thymic emigrants (RTE), are distinguished by the presence of high levels of TCR excision circles (TRECs), CD31, and show the greatest amount of TCR repertoire diversity. Antigen stimulation results in upregulation of activation markers and differentiation into effector cells. Effector cells are short-lived cells that are largely responsible for clearance of the offending antigen. A large number of markers have been used to characterize T-cell activation, including HLA-DR, CD25, and CD38. Memory T-cells are defined as long-lived T-cells that have experienced their cognate antigen. As antigen-experienced cells, most memory T-cells express CD45R0 and lack CD45RA and home to secondary lymphoid organs or recently infected tissues.
The purpose of this assay is to determine the composition of na´ve, recent thymic emigrants (RTEs), activated, effector and memory T cells based on differential expression of CD3, CD4, CD8, CCR7, CD45RA, CD31, HLA-DR, and CD38 by flow cytometry.