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The mystery of antigen presentation: How do antigen-presenting cells alter our immune response?
Antigen-presenting cells (APCs) play a vital role in our immune system. These cells display antigens in the form of major histocompatibility complex (MHC) proteins, which subsequently interact with the T cell's receptors. This process enables the precise and flexible immune response necessary not only to face foreign pathogens, but also to initiate defenses when abnormal cells, such as cancer cells, appear.
Antigen presentation enables the specificity of adaptive immunity, which not only contributes to the response to internal and external pathogens but is also involved in the defense against tumors.
What are antigen-presenting cells?
Antigen-presenting cells can be divided into two categories: professional and non-professional according to their professionalism. Professional antigen-presenting cells mainly include dendritic cells, macrophages, and B cells, which have powerful antigen endocytosis and presentation capabilities. These cells capture antigens from the environment, process them, and present them again to T cells as MHC proteins and costimulatory molecules.
Professional antigen-presenting cells
Professional antigen-presenting cells such as dendritic cells can effectively present antigens and play a central role in the process of T cell activation. When these cells capture the antigen, their surface MHC II increases and is displayed to helper T cells, thereby generating a further immune response.
Diversity of dendritic cells
Dendritic cells have the broadest antigen presentation capabilities and can stimulate both helper and cytotoxic T cells. They perform what is called cross-presentation, a process in which foreign antigens are presented to cytotoxic T cells, enabling their activation. This function not only helps fight pathogens but also plays a role in preventing autoimmune diseases.
Before dendritic cells recognize foreign antigens, the number of MHC II and co-stimulatory molecules on their surface is very low. However, once activated, they will become effective professional antigen-presenting cells.
Macrophages and B cells
After being stimulated by T cells, macrophages can express MHC II and a variety of costimulatory molecules, which allows them to present phagocytized antigens to helper T cells. In contrast, B cells can directly recognize the antigen in the solution and present it to helper T cells after endocytosis, but this process is called the difference in antigen presentation.
The role of non-professional antigen-presenting cells
Non-professional antigen-presenting cells refer to all cells with a nucleus. Such cells typically display endogenous peptides via MHC I molecules; they generally do not express MHC II. However, in some cases, they can also perform antigen presentation, promoting immune responses to specific pathogens.
The presence of non-professional antigen-presenting cells expands the immune system's ability to respond to a variety of scenarios, although these cells are not commonly used to activate T cells on primary contact.
Interaction between T cells and antigen-presenting cells
After dendritic cells capture pathogens, they often migrate to lymph nodes, which are important sites for interaction between antigen-presenting cells and T cells. After mature dendritic cells change their surface expression of MHC and costimulatory molecules, this change enables them to effectively activate T cells.
Application in cancer treatment
In the treatment of cancer, the role of antigen-presenting cells is particularly important. These cells stimulate B cells and cytotoxic T cells to fight tumor-associated antigens. Therefore, dendritic cell-based cancer therapies are being researched and developed with the aim of using artificial antigen-presenting cells to strengthen the patient's immune system and specifically target malignant cells.
The latest treatments even include genetically engineered artificial antigen-presenting cells designed to enhance the immune system's attack on cancer cells.
How antigen-presenting cells precisely regulate our immune system shows the mystery of life. Have you ever thought about the complex mechanisms and effectiveness behind all this?
