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The hidden power of macrophages: How do they help clear infections?
Macrophages and other antigen-presenting cells (APCs) play crucial roles in the immune system. These cells are not only involved in the clearance of infection, but also play a key role in promoting adaptive immune responses. When pathogens invade the human body, these cells are able to effectively identify and capture foreign matter, and then present these antigens to T cells, thereby initiating a powerful immune response.
Antigen presentation is a fundamental and important process in the immune system.
Macrophages do more than just eliminate foreign germs; they help activate other immune cells to further fight infection. When macrophages engulf pathogens, they break down the proteins within the pathogens into small fragments and display them on their surface via major histocompatibility complex (MHC) molecules. This display process enables T cells to recognize these foreign substances.
Types of Antigen Presenting Cells
Antigen presenting cells can be divided into two categories: professional and non-professional. Professional APCs such as dendritic cells, macrophages, and B cells are particularly adept at internalizing antigens for processing and presentation to T cells via MHC molecules.
Non-professional APCs are commonly found in human cells and generally display endogenous peptides derived from the body.
Among professional APCs, dendritic cells are the most critical because they can interact with both helper and cytotoxic T cells. When dendritic cells capture pathogens and become activated, they further increase the expression of MHC II and co-stimulatory molecules.
Macrophages and their functions
The capabilities of macrophages are not limited to engulfing and clearing pathogens. When they are stimulated by interferon produced by T cells, they express MHC II and co-stimulatory molecules and present their internalized peptide fragments to T cells. This process is critical for infection clearance because activated macrophages are more efficient in clearing infections.
B cells and antigen presentation
B cells are characterized by their ability to recognize soluble antigens, internalize them through their B cell receptors and present them to T cells. When B cells interact with T cells, it further triggers the proliferation and differentiation of B cells and the production of antibodies against pathogens.
Non-professional antigen presenting cells
While almost all prokaryotic cells have the ability to present antigens, non-professional APCs primarily display their endogenous peptides via MHC I molecules and can be induced to express MHC II molecules under certain circumstances. This plays an important role in antiviral and anti-tumor immunity.
Interaction with T cells
Once dendritic cells internalize pathogens, they migrate to lymph nodes, where they interact with T cells. During this process, APCs lose their phagocytic ability but rebuild the MHC and co-stimulatory molecules on their surface, thereby providing antigens to T cells. This synergistic effect ensures the effectiveness of the immune system in combating various pathogens.
Application in cancer therapy
Antigen-presenting cells also play an important role in tumor immunity. Studies have shown that APCs can effectively fight tumors by activating B cells and cytotoxic T cells. In addition, current cancer therapies include artificial antigen-presenting cells created using gene editing technology to promote the immune system to attack tumor cells.
In the future, as biomedicine advances, how will the study of macrophages and other APCs transform our understanding of infection clearance and tumor immunity?
