When does the immune system become active?

The immune system becomes active when it detects the presence of foreign substances or pathogens in the body. These foreign substances can be bacteria, viruses, fungi, or other microorganisms that can cause disease. When these pathogens enter the body, the immune system responds by activating various mechanisms to identify, neutralize, and eliminate them.

The initial activation of the immune system occurs when specialized immune cells, such as macrophages and dendritic cells, detect the presence of foreign antigens or pathogens. These cells then present the antigens to other immune cells, such as T cells and B cells. T cells recognize and attack infected cells or foreign invaders directly, while B cells produce antibodies that specifically target and neutralize the pathogens.

Once the immune system is activated, it undergoes a process called the immune response. This involves a complex series of interactions and communications between different immune cells, signaling molecules, and effector mechanisms to effectively eliminate the pathogens. The immune response can be categorized into two main types: innate immunity and adaptive immunity.

Innate immunity is the first line of defense and is activated immediately upon detecting pathogens. It involves physical barriers, such as skin and mucous membranes, as well as chemical barriers, such as stomach acid and antimicrobial substances. Innate immune cells, such as macrophages and natural killer cells, are also part of innate immunity and can recognize and attack foreign invaders non-specifically.

Adaptive immunity is the more specialized and targeted response of the immune system. It develops over time as the body encounters specific pathogens and develops immunological memory. Adaptive immune cells, such as T cells and B cells, undergo a process of clonal expansion and differentiation to produce a large number of antigen-specific cells that can directly attack or neutralize the pathogens.

The activation of the immune system is essential for maintaining health and preventing disease. By recognizing and responding to foreign substances and pathogens, the immune system helps protect the body from infections, illnesses, and other potential health threats.