Memory T cells are a crucial component of the adaptive immune system, providing long-lasting immunity after an infection has been cleared. These cells are not a homogenous population, but rather are composed of several subsets, each with distinct characteristics and functions. The primary subsets of memory T cells include central memory T cells (Tcm cells), effector memory T cells (Tem cells), and terminally differentiated effector memory T cells re-expressing CD45RA (Temra cells).
Key Subsets of Memory T Cells
Here's a breakdown of the main memory T cell subsets:
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Central Memory T Cells (Tcm):
- Location: Primarily found in secondary lymphoid organs (e.g., lymph nodes, spleen).
- Characteristics: Express the lymph node homing receptors CCR7 and CD62L. Exhibit high proliferative capacity upon antigen re-encounter.
- Function: Rapidly expand and differentiate into effector cells upon encountering their specific antigen in the lymph nodes, playing a key role in initiating a secondary immune response.
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Effector Memory T Cells (Tem):
- Location: Circulate in the blood and can migrate to non-lymphoid tissues, including sites of inflammation.
- Characteristics: Lack CCR7 and CD62L expression. Exhibit immediate effector function upon antigen stimulation.
- Function: Provide rapid protection at the site of infection by immediately producing effector cytokines and performing cytotoxic functions.
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Terminally Differentiated Effector Memory T Cells Re-expressing CD45RA (Temra):
- Location: Circulate in the blood.
- Characteristics: Lack CCR7 and CD62L expression and re-express CD45RA (a marker typically found on naive T cells). Exhibit immediate effector function, similar to Tem cells, but are generally considered to be more differentiated.
- Function: Provide rapid protection in peripheral tissues, contributing to immediate immune responses, particularly in aged individuals. However, their proliferative capacity is typically reduced compared to Tem and Tcm cells.
The different subsets allow for a diversified and effective immune response. Tcm cells contribute to long-term immunity and rapid response in lymphoid organs, while Tem and Temra cells provide immediate protection at the site of infection.
