Question

MHC molecules are used for antigen ________ to T cells.

Short answer

presentation

Step-by-step solution

Understanding the role of MHC molecules in the immune system

Major Histocompatibility Complex (MHC) molecules are essential in the immune system for presenting peptide fragments to T cells. These peptides are usually derived from pathogens and are displayed on the cell surface by MHC molecules.

Identifying the correct biological term for the process

The process of displaying antigen fragments to T cells is known as antigen presentation. Therefore, the term that fills the blank should describe this specific function of MHC molecules.

Completing the sentence with the appropriate term

Given the role of MHC molecules, the correct term to complete the sentence is 'presentation'. The completed sentence is: MHC molecules are used for antigen presentation to T cells.

Key concepts

MHC Molecules

The immune system operates like a highly specialized security team, constantly surveilling for signs of intrusion. Among the key players in this defense mechanism are the Major Histocompatibility Complex (MHC) molecules. These molecules are akin to identification badges that present a snapshot of the cellular environment.
MHC molecules exist in two main classes: Class I MHC are found on almost all cells and present peptides to CD8+ T cells, while Class II MHC are primarily on the surface of antigen-presenting cells (APCs) such as dendritic cells, macrophages, and B cells, engaging with CD4+ T helper cells.
When a cell is infected by a virus or bacteria, MHC molecules help to present specific peptides—tiny pieces of protein—from the pathogen on the cell surface. This is a crucial step in mobilizing the immune response, acting as a 'red flag' to attract T cells that recognize these peptides as foreign.

Immune System

Understanding the immune system is paramount for grasping the significance of antigen presentation. This complex network of cells, tissues, and organs works synergistically to protect the body against disease-causing organisms, which are referred to as pathogens.

• The innate immune system offers immediate, non-specific defense against pathogens.
• The adaptive immune system provides a specialized and long-lasting response.

The adaptive arm, where T cells and antigen presentation play a pivotal role, tailors its response to specific pathogens. Antigens are substances that the immune system can detect as foreign, triggering an immune response. The antigen presentation by MHC molecules is a critical initiation event, enabling T cells to recognize and mount a targeted attack against these invaders.

T Cells

T cells are a type of lymphocyte, a subset of white blood cells, playing an essential role in the immune response. These cells mature in the thymus, which is where the ‘T’ in T cells comes from.
T cells are primarily involved in the adaptive immune system and can be categorized into various types, each with a specific function:

• Cytotoxic T cells (CD8+): Directly destroy infected or cancerous cells.
• Helper T cells (CD4+): Coordinate the immune response by secreting signaling molecules called cytokines.
• Regulatory T cells: Help to modulate the immune response and prevent autoimmunity.

Antigen presentation to T cells is vital for the activation of cytotoxic and helper T cells. Once activated by recognizing an antigen presented by MHC molecules, T cells proliferate and perform their respective functions to eliminate the pathogens or infected cells.