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Immune System

The Immune System

The immune system has evolved to recognize and kill cells infected with pathogens and, in most cases, to avoid attacking healthy tissues. Making this distinction requires discrimination between what is harmless to the body, and therefore should be ignored, and what is foreign and potentially dangerous, and therefore should be eliminated. This same immunological mechanism also plays an important role in killing and removing damaged or transformed cells that, if not controlled, could lead to cancer.

When this mechanism is dysregulated, it can cause autoimmune diseases in which the immune system targets and damages healthy cells.

Immune health is achieved through the balance of diseased cell killing and tolerance against healthy tissue.

Immune Science

There are two distinct arms of our immune system:

  • The innate immune system is the first line of defense against pathogens, providing a non-specific and immediate response.
  • In contrast, the adaptive immune system leverages T cells and B cells to mount a highly specific response through the use of specialized immune receptors.

T cells (also called T lymphocytes) are a major component of the adaptive immune system. Our bodies have many millions of different T cells. Each T cell will develop its own T cell receptor (TCR) that is specific for a particular antigen (tiny piece of pathogen or virus that is displayed on a cell’s surface). T cells constantly scan other cells for an antigen match. Their roles include directly killing infected host cells, activating other immune cells, and regulating the immune response.

T cells are activated every day as our bodies defend against disease-causing antigens. Harnessing this power requires a deep understanding of the codes that activate them, and that code is determined by the immune synapse, the key interface of cell-mediated immunity and the molecular interface through which a T cell interacts with an antigen-presenting cell.

Synapse photo 1 5x
T cell engaging an antigen presenting cell

The Immune Synapse

The immune synapse is central to cellular immunity. The immune synapse is the interface between a T cell and a cell that presents an intracellular antigen. Specific receptors on the T cell, known as T cell receptors, or TCRs, recognize specific antigens. Unique TCR-antigen pairs define unique immune synapses. Such synapses govern the response of the T cell.

The Role of MHCs

The major histocompatibility complex (MHC) is responsible for the coding of proteins that the immune system uses to identify cells and tissues in the body as “self” or “other”. MHC molecules "talk" to T cells that patrol the body for foreign invaders or dangerously mutated cells. The MHC acts as a window into our cells. It presents snippets of information (peptides) on the state of the cell – allowing the immune system to check for infection, cancer, and other maladies. Cells that do not pass the self/other test are eliminated.

MHC molecules comprise two individual parts that present short epitopes (short peptides) to cells of the immune system. There are two main classes of MHC molecule – Class I and Class II.

Class 1 mhc

Class I MHC


  • Found on all nucleated cells in the body and on platelets.
  • Interacts with CD8+ T cells, interacting directly with CD8 as a co-receptor. Presentation of intracellular epitopes allows T cells to check for intracellular bacteria, viral infection and cancerous mutations. MHC I present epitopes of 8-10 amino acids to T cells, and serve as a global “alarm” system for the cells in the body.
Class 2 mhc

Class II MHC


  • Typically found on antigen presenting cells (APC) such as macrophages, dendritic cells, and B lymphocytes. These MHC molecules interact with CD4 on CD4+ T helper cells.
  • Presentation functions as a specific line of communication between immune cells and the global immune system.
  • Presentation is a requirement for initiating and sustaining adaptive immune responses against foreign invaders such as fungi and extracellular bacteria.

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