Which of the following immune cells/molecules are most effective at destroying intracellular pathogens?
a. T helper cells
b. B cells
c. Antibodies
d. Complement
e. T cytolytic cells
The correct answer and explanation is :
The correct answer is e. T cytolytic cells.
Explanation:
Intracellular pathogens, such as viruses and certain bacteria (e.g., Mycobacterium tuberculosis), infect host cells and replicate inside them, making it difficult for the immune system to detect and destroy these pathogens. The immune cells or molecules that are most effective at eliminating these types of infections are those that can recognize and kill infected host cells directly.
T Cytolytic Cells (CD8+ T Cells):
T cytolytic cells, also known as CD8+ T cells or cytotoxic T lymphocytes (CTLs), are specialized immune cells that can directly kill infected cells. These cells recognize infected host cells through the major histocompatibility complex class I (MHC-I) molecules on the surface of the cells. When a host cell becomes infected, fragments of the intracellular pathogen (antigens) are processed and presented on MHC-I molecules. The T cytolytic cells, with the help of their T-cell receptor (TCR), bind to these MHC-I/antigen complexes and become activated. Once activated, cytotoxic T cells release enzymes, such as perforin and granzymes, which create pores in the infected cell membrane and induce apoptosis (programmed cell death), thereby eliminating the infected cells and preventing further replication of the pathogen.
Why Not the Other Options?
- a. T helper cells (CD4+ T cells): T helper cells play a crucial role in coordinating the immune response but do not directly kill infected cells. They secrete cytokines that help activate other immune cells like B cells and cytotoxic T cells, but they are not directly involved in the destruction of intracellular pathogens.
- b. B cells: B cells are responsible for producing antibodies, which are effective at neutralizing extracellular pathogens or toxins. However, they do not have the capacity to kill cells directly or target intracellular pathogens.
- c. Antibodies: Antibodies are proteins produced by B cells that can bind to pathogens in the extracellular space, neutralizing or marking them for destruction by other immune cells like macrophages. They do not directly kill infected cells, so they are less effective against intracellular pathogens.
- d. Complement: The complement system is a set of proteins that can help destroy pathogens by forming membrane attack complexes (MACs) and promoting inflammation. While complement can contribute to the immune defense, it is generally more effective against extracellular pathogens, not intracellular ones.
In summary, T cytolytic cells are the most effective at destroying intracellular pathogens due to their ability to directly recognize and kill infected host cells.