T Cells

Original Editor - Lucinda hampton

Top Contributors - Lucinda hampton and Vidya Acharya  

Introduction

T lymphocytes are a critical part of the adaptive immune system safeguarding against infection and malignancy, but also implicated in many immune pathologies. T cells arise from bone marrow and mature in the thymus.

There are various types of T cells namely:

• CD8+ T Cells (cytotoxic T cells, or killer T cells): actively destroy infected cells through the use of granule sacs that contain digestive enzymes.
• CD4+ T cells (helper T cells): activate cytotoxic T cells, macrophages, and stimulate antibody production by B cell lymphocytes.
• Regulatory T cells: suppress the actions of B and T cells to decrease the immune response when a highly active response is no longer warranted.
• Natural Killer T cells: distinguish infected or cancerous cells from normal body cells and attack cells that do not contain molecular markers that identify them as body cells.
• Memory T cells: protect against previously encountered antigens and may provide lifetime protection against some pathogens.

Mode of Action

T cells cannot recognize soluble, free antigens, they can only recognize protein-based, receptor-bound antigens. This recognition occurs via the use of the MHC (major histocompatibility complex) also known as HLA(human leucocyte antigen) 1 and 2 receptors, which along with the TCRs (T-cell receptors) bind the antigen it seeks and form a complex that allows the T cell to remember the antigen.

1. CD4+ T cells recognize MHC 2 bound antigens
2. CD8+ T cells recognize MHC 1 bound antigens.

Both CD4+ T cells and CD8+ T cells have the TCR (and the co-receptor CD3).

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