How your body kills infected cells with a special type of immunity
Imagine you are infected with a virus that invades your cells and uses them to make more copies of itself. How does your body detect and destroy these infected cells before they spread the virus to other cells? The answer lies in a special type of immunity that your body develops over time, called cell-mediated immunity.
Cell-mediated immunity is a part of your immune system, which is your body’s defense system against harmful substances and organisms, such as bacteria, viruses, fungi, parasites, and even cancer cells. Your immune system has two main types: innate immunity and cell-mediated immunity.
Innate immunity is the immunity that you are born with. It consists of physical barriers, such as your skin and mucous membranes, and general immune cells, such as phagocytes and natural killer cells, that can recognize and destroy common types of germs. Innate immunity is fast and effective, but it is not very specific or long-lasting.
Cell-mediated immunity is the immunity that you acquire during your lifetime. It consists of specialized immune cells and molecules that can recognize and eliminate specific types of germs and tumor cells. Cell-mediated immunity is slower and more complex than innate immunity, but it is more specific and long-lasting.
Cell-mediated immunity works by using T cells, which are a type of immune cells that can recognize and kill infected or abnormal cells. T cells have receptors on their surface that can bind to antigens presented by other cells. Antigens are any substances that trigger an immune response. T cells can either help other immune cells by secreting chemicals called cytokines, or directly kill infected or abnormal cells by releasing substances that create holes and trigger cell death. Cell-mediated immunity is especially good at fighting off germs that live inside your cells, such as viruses and some bacteria.
Cell-mediated immunity requires the activation of naive T cells by antigen-presenting cells (APCs), such as dendritic cells, macrophages, and B cells. APCs capture and process antigens from germs or their products and present them to naive T cells in the lymph nodes or other organs. Naive T cells are T cells that have not encountered their specific antigen yet. When a naive T cell binds to its specific antigen on an APC, it becomes activated and multiplies into many copies of itself. Some of these copies become effector T cells that carry out the immune response against the germ, while others become memory T cells that can remember and respond faster and stronger to the same antigen in the future.
Cell-mediated immunity is important because it provides us with a lasting defense system that can be used against new and varying germs. The diversity of T cell receptors is generated by a process called somatic recombination, which randomly shuffles and rearranges segments of genes that encode these molecules in developing T cells. This process creates millions of different combinations of T cell receptor specificities that can recognize virtually any antigen. Moreover, some T cells undergo somatic hypermutation, which introduces small changes in the T cell receptor genes at a high rate, resulting in T cells with higher affinity for the antigen.
Cell-mediated immunity is also regulated by various mechanisms to prevent excessive or inappropriate responses that could harm us. For example, some T cells act as regulatory T cells that suppress the activity of other immune cells to maintain tolerance to our own antigens and prevent autoimmune diseases. Additionally, some cytokines act as anti-inflammatory agents that modulate the intensity and duration of the immune response.
In summary, cell-mediated immunity is a sophisticated and dynamic system that protects us from a variety of germs and tumors. It involves specialized immune cells and molecules that recognize and eliminate foreign antigens with high specificity and memory. It also involves genetic mechanisms that generate diversity and regulation of the immune response.
Reference Links
• Cell-mediated immunity – Wikipedia – This article provides an overview of cell-mediated immunity, its history, components, functions, and mechanisms. It also explains how cell-mediated immunity differs from humoral immunity and innate immunity.
• 14.1: Cell-Mediated Immunity – An Overview – Biology LibreTexts – This article gives a detailed explanation of cell-mediated immunity, its role in fighting off germs that live inside the cells, and its various immune cells and molecules. It also provides examples and illustrations to help understand the concepts.
• Cell-mediated Immunity | Pathway Medicine – This article describes the cell-mediated immunity in depth, including the activation of T cells by antigens and antigen-presenting cells, the production and secretion of cytokines by helper T cells, and the killing of infected or abnormal cells by cytotoxic T cells.