Question

Cells that process foreign proteins and complex them with their MHC proteins are called a. cytotoxic T cells. b. plasma cells. c. NK cells. d. antigen-presenting cells. e. helper T cells.

Short answer

The correct answer is 'd. antigen-presenting cells.' These are the cells that process foreign proteins and complex them with their MHC proteins.

Step-by-step solution

Recognizing the Role of Cells

The crucial step for this exercise is to recognize the roles of each of the cell types listed. In this context, the need is to identify which cell process foreign proteins and complexes them with their MHC proteins.

Isolate the Correct Cell Type

Understanding the function of each cell type, we can isolate the cell type called antigen-presenting cells (APCs) as the one responsible for processing foreign proteins and complexing them with MHC proteins. APCs are a type of cell within our immune system that takes foreign proteins, processes them, and complexes them with MHC proteins, thereby presenting them to other immune cells.

Identify the Function

Knowing the function of the antigen-presenting cells in the processing of foreign proteins and complexing them with MHC proteins, we can now choose the correct cell type from the options given. Therefore, the favourable answer is 'd. antigen-presenting cells.'

Key concepts

MHC Proteins

Major Histocompatibility Complex (MHC) proteins are essential molecules in the immune response mechanism. These molecules reside on the surface of cells and are pivotal for the identification and presentation of foreign particles, known as antigens, to the immune system. There are two main classes of MHC proteins: Class I MHC proteins, which are found on the surface of nearly all body cells, and Class II MHC proteins, which are expressed predominantly on immune cells known as antigen-presenting cells (APCs).

Class I MHC proteins present antigen fragments to cytotoxic T cells, which are equipped to kill cells infected by viruses or transformed by cancer. Class II MHC proteins, on the other hand, present antigens to helper T cells, which play a vital role in orchestrating the immune response, such as stimulating the production of antibodies by B cells. This functionality of MHC proteins to present antigenic peptides to T cells is a central element to the adaptive immune response, ensuring that the body can recognize and respond to a vast array of foreign challenges.

Immune System Cells

The immune system is comprised of various cells, each playing a specific role to protect the body from infections and diseases. This complex network involves white blood cells or leukocytes, which include lymphocytes (like T cells and B cells), monocytes, neutrophils, eosinophils, and basophils. Lymphocytes are particularly significant in the adaptive immune response.

Lymphocytes

There are two main types of lymphocytes: B cells and T cells. B cells are responsible for antibody production, while T cells, divided into helper T cells and cytotoxic T cells, perform different roles in cellular immunity. Helper T cells facilitate the activation and coordination of other immune cells, whereas cytotoxic T cells eliminate compromised cells. Another crucial type of lymphocytes are the natural killers (NK) cells, which play a role in the innate immune system by destroying infected or cancerous cells without prior sensitization.

Antigen-Presenting Cells (APCs)

APCs, such as dendritic cells, macrophages, and certain B cells, perform the critical task of capturing antigens and presenting them to T cells. This triggers a tailored immune response, central to the body's ability to fight off specific pathogens and to develop immunity.

Processing Foreign Proteins

Processing foreign proteins is a complex feat performed by antigen-presenting cells (APCs). When a pathogen, like a virus or bacterium, invades the body, it is recognized by its foreign proteins, also known as antigens. APCs have the task of engulfing these pathogens and breaking them down into smaller fragments.

Once a pathogen is internalized, the APCs degrade it into peptide fragments that can be loaded onto MHC molecules. This process is termed antigen processing. Following processing, the antigen-MHC complex is transported to the surface of the APC where it can be 'presented' to T cells. This interaction is crucial as it leads to the activation of T cells, which will initiate a cascade of immune responses tailored to target the specific antigens. It is through these processes that the immune system can effectively identify and neutralize harmful pathogens.