• How antigens are produced
Antigens are produced by various cells in the body, including immune cells such as B cells and dendritic cells. These cells have the ability to recognize and respond to foreign substances, known as antigens, which enter the body.
When an antigen is encountered, immune cells engulf it and break it down into smaller fragments. These fragments are then presented on the surface of the immune cells in combination with major histocompatibility complex (MHC) molecules.
This complex of antigen fragment and MHC molecule is recognized by other immune cells, such as T cells, which then activate and proliferate. This process triggers an immune response, leading to the production of specific antibodies against the antigen.
In addition, certain cells in the body, such as cancer cells or infected cells, may produce abnormal or altered proteins that are recognized as foreign by the immune system. These proteins can also act as antigens and generate an immune response.
Antigens are produced through a process called antigen processing and presentation. Here are the step-by-step details:
1. Antigens, which are typically foreign substances or molecules, enter the body through various routes such as inhalation, ingestion, or injection.
2. Once inside the body, antigen-presenting cells (APCs), such as macrophages, dendritic cells, or B cells, recognize and capture the antigens.
3. APCs break down the captured antigens into smaller fragments through a process known as antigen processing. This can occur through intracellular degradation or extracellular processing, depending on the type of antigen and the APC involved.
4. Intracellular degradation: In this process, the antigens are engulfed by the APCs through endocytosis or phagocytosis. The antigens are then transported to acidic compartments called endosomes or lysosomes.
5. Within the endosomes or lysosomes, the antigens are degraded by enzymes, such as proteases, into smaller peptide fragments. This process is often facilitated by the low pH environment of these compartments.
6. Extracellular processing: Some antigens, especially those derived from extracellular pathogens, are processed by enzymes outside the APCs. This external processing can be carried out by enzymes secreted by the APC or by proteases from pathogens themselves.
7. Regardless of the processing method, the resulting peptide fragments (epitopes) associate with special proteins called major histocompatibility complex (MHC) molecules inside the APCs. In humans, MHC molecules are also known as human leukocyte antigens (HLAs).
8. The MHC molecules function to "present" the antigen fragments on the surface of the APCs. This process is called antigen presentation.
9. The MHC-antigen complex is then recognized by specific lymphocytes called T cells, which have T cell receptors (TCRs) on their surface. T cells constantly survey the body for MHC molecules with bound antigens.
10. If a T cell encounters an MHC-antigen complex that matches its specific TCR, it triggers an immune response. This recognition is known as T cell receptor recognition.
11. The activated T cells then initiate a cascade of immune responses, including the production of antibodies by B cells, activation of other immune cells, and the release of cytokines that stimulate the immune system.
In summary, antigens are produced through antigen processing and presentation, where APCs capture, process, and present antigens to T cells, initiating an immune response.