Question

Cytotoxic T cells will bind with their TCR to which of the following? a. antigens presented with MHC I molecules b. antigens presented with MHC II molecules c. free antigen in a soluble form d. haptens only

Short answer

a. antigens presented with MHC I molecules

Step-by-step solution

Assess the Function of Cytotoxic T Cells

First, understand the role of Cytotoxic T cells in the immune system. They are primarily responsible for killing virus-infected cells, tumor cells, and sometimes pathogen-infected cells. They recognize these infected cells through presented antigens on MHC (Major Histocompatibility Complex) molecules.

Understand MHC Molecule Types

There are two main classes of MHC molecules: Class I and Class II. MHC I molecules are found on all nucleated cells and present endogenous antigens, while MHC II molecules are present mainly on professional antigen-presenting cells (APCs) and present exogenous antigens.

Match Cytotoxic T Cells with MHC Molecule

Know that Cytotoxic T cells, also known as CD8+ T cells, generally recognize antigens presented by MHC I molecules. This is part of their mechanism to target and destroy infected or dysfunctional cells.

Evaluate the Answer Choices

Match what has been learned from the previous steps to the choices given: a) antigens presented with MHC I molecules are indeed what Cytotoxic T cells recognize, b) is incorrect as MHC II usually correlates with helper T cells not cytotoxic, c) cytotoxic T cells do not typically engage free antigens in solution, and d) haptens by themselves without being presented by MHC molecules, are not the typical way cytotoxic T cells recognize antigens.

Key concepts

MHC I Molecules

The role of Major Histocompatibility Complex (MHC) Class I molecules is pivotal in the immune system, particularly in the context of viral infections, tumor surveillance, and transplant rejection. These molecules are found on the surface of nearly all nucleated cells in the body.

The primary function of MHC I is to exhibit fragments of proteins, called peptides, from within the cell to the surface where they can be surveyed by T cells. This can include normal cellular proteins as well as foreign, potentially harmful proteins such as those from a virus. This is akin to a cellular 'identity card' that provides T cells with a snapshot of the cell's internal environment.

When these MHC I molecules present antigen peptides that are recognized as foreign, they trigger an immune response, particularly from cytotoxic T cells. Cytotoxic T cells have specialized receptors, called T Cell Receptors (TCR), that can specifically recognize and bind to these peptide-MHC I complexes. This is usually the first step in the immune response to infected or malignant cells.

Immune System

The immune system is an intricate network of cells, tissues, and organs that work together to defend the body against attacks by 'foreign' invaders, such as bacteria, viruses, fungi, and cancer cells. It is broadly classified into two categories: innate immunity and adaptive immunity.

Cytotoxic T cells fall under the adaptive immune system, which is characterized by its ability to remember and respond more effectively to pathogens that it has encountered before. These cells have a specific role within the adaptive immune response: to seek out and destroy cells that have been compromised. They are especially effective against cells infected with viruses and cells that have turned cancerous because these cells express abnormal proteins, which can be presented by MHC I molecules to cytotoxic T cells.

This adaptive system ensures that once the body has successfully fought off an initial infection, it can more rapidly and efficiently react to subsequent infections by the same agent, a principle utilized in vaccinations.

Antigen Presentation

Antigen presentation is a complex process that is vital to the immune system's ability to recognize and mount a response against pathogens. It involves the display of antigens on cell surfaces by MHC molecules. There are two types, the MHC I and MHC II molecules, each serving a unique purpose.

MHC I molecules present endogenous antigens, which are typically derived from the normal turnover of proteins within the cell or from proteins produced during an infection, such as viral proteins. Antigen presenting cells can also take up antigens from the outside, process them, and present them on MHC I. This activates cytotoxic T cells to target and destroy these compromised cells.

On the other hand, MHC II molecules are primarily found on 'professional' antigen-presenting cells, like dendritic cells, macrophages, and B cells. They specialize in presenting exogenous antigens that have been ingested or engulfed by a cell, to helper T cells. It is crucial in the initiation and regulation of the adaptive immune responses.