The first line of defense for the immune system is the skin and mucous membranes. These layers of the body form a physical barrier that prevents microorganisms from entering the body. However, when these barriers are breached, the immune system must respond quickly. That's when white blood cells, also known as leukocytes, come into play. These specialized cells are produced in bone marrow and are essential to the immune system's function. There are two main types of leukocytes: phagocytes and lymphocytes. Phagocytes are responsible for engulfing and destroying foreign particles, while lymphocytes are responsible for identifying and destroying specific harmful agents in the body.
When a pathogen enters the body, phagocytes quickly rush to the site of infection to engulf the foreign invaders. Once inside the phagocyte, the pathogen is destroyed by enzymes, and the remaining parts are presented on the cell surface. This process is known as antigen presentation and is crucial to the immune system's ability to recognize and remember harmful agents. The presented antigens are then recognized by the lymphocytes, which activate an immune response tailored to the specific pathogen. This process is known as adaptive immunity and is the primary reason vaccines work. A vaccine exposes the body to a non-harmful version of the disease, allowing the lymphocytes to recognize and respond to it more efficiently in the future.
The immune system is also responsible for regulating inflammatory responses in the body. Inflammation is a crucial part of the immune system's response to infection as it helps to isolate and destroy the pathogen. However, excessive inflammation can be harmful, leading to tissue damage and chronic diseases. The immune system utilizes various molecules, known as cytokines, to regulate inflammation levels. These cytokines can either increase or decrease inflammation levels in the body, depending on the immune system's needs.
The immune system's final line of defense against harmful agents is the production of antibodies. Antibodies are proteins produced by B lymphocytes and are specific to a certain antigen. They are responsible for neutralizing harmful pathogens to prevent further infection. Antibodies can also work in conjunction with phagocytes to enhance pathogen destruction. This process is known as opsonization and makes pathogen destruction more efficient.