Cellular immunity

Cellular Immunity

Cellular immunity is a critical component of the adaptive immune system, primarily involving the activation of T cells and the release of cytokines in response to an antigen. Unlike humoral immunity, which relies on the production of antibodies by B cells, cellular immunity does not involve antibodies but instead depends on the direct action of immune cells.

Overview

Cellular immunity is essential for the defense against intracellular pathogens such as viruses, some bacteria, and cancer cells. It is mediated by several types of T cells, including cytotoxic T cells (CD8+ T cells), helper T cells (CD4+ T cells), and regulatory T cells. These cells recognize antigens presented by major histocompatibility complex (MHC) molecules on the surface of infected or abnormal cells.

Mechanism

Antigen Presentation

The process begins with the presentation of antigens by antigen-presenting cells (APCs) such as dendritic cells, macrophages, and B cells. These cells process the antigens and present them on their surface using MHC molecules. MHC class I molecules present antigens to CD8+ T cells, while MHC class II molecules present to CD4+ T cells.

T Cell Activation

Upon recognition of the antigen-MHC complex, T cells become activated. CD8+ T cells, also known as cytotoxic T lymphocytes (CTLs), directly kill infected or cancerous cells by inducing apoptosis. CD4+ T cells, or helper T cells, secrete cytokines that enhance the immune response by activating other immune cells, including B cells and macrophages.

Memory T Cells

After the resolution of an infection, some T cells become memory T cells, which persist in the body and provide a faster and more robust response upon re-exposure to the same antigen.

Role in Disease

Cellular immunity plays a crucial role in controlling infections and preventing the spread of cancer. However, dysregulation of cellular immunity can lead to autoimmune diseases, where the immune system attacks the body's own tissues, or immunodeficiency, where the immune response is inadequate.

Clinical Applications

Understanding cellular immunity is vital for the development of vaccines, immunotherapy for cancer, and treatments for autoimmune diseases. For example, CAR T-cell therapy is a form of immunotherapy that involves engineering a patient's T cells to better recognize and attack cancer cells.

Also see

• Humoral immunity
• Adaptive immune system
• Antigen-presenting cell
• Cytokine
• Major histocompatibility complex