Immunization

Immunization

Immunization, also known as immunisation, is the process through which an individual's immune system is strengthened against an agent, known as the immunogen.

When the immune system encounters foreign molecules (non-self), it triggers an immune response and develops the ability to respond rapidly upon subsequent encounters (through immunological memory). This function is carried out by the adaptive immune system. By exposing an individual to an immunogen in a controlled manner, the body can learn to defend itself, a process known as active immunization.

The key components of the immune system enhanced by immunization are B cells (and the antibodies they produce) and T cells. Memory B cells and memory T cells enable a swift response upon encountering a foreign molecule again. Passive immunization involves directly introducing these elements into the body, rather than relying on the body to produce them.

Immunization is accomplished through various techniques, with vaccination being the most common. Vaccines against disease-causing microorganisms prime the immune system to fight or prevent infections. The concept of therapeutic cancer vaccines is based on mutations that cause cancer cells to produce unfamiliar proteins or molecules. Additionally, experimental vaccines targeting molecules like nicotine (NicVAX) or the hormone ghrelin are being explored.

Immunization can be achieved actively or passively. Vaccination represents active immunization, where a foreign molecule is introduced into the body, prompting the body to generate immunity against it. This immunity is conferred by T cells and B cells with their antibodies.

Active immunization can occur naturally when an individual encounters a microbe for the first time. The immune system responds by producing antibodies and other defenses against the microbe, providing immunity upon subsequent exposure. Artificial active immunization involves injecting the microbe or its components into the body before natural exposure occurs, as seen with attenuated vaccines.

Passive immunization involves transferring pre-made elements of the immune system to a person, bypassing the need for the body to produce them. Currently, antibodies are used for passive immunization, offering rapid but short-lasting protection as they are naturally broken down. Physiological passive immunization occurs when antibodies are transferred from mother to fetus during pregnancy, providing protection during and shortly after birth.

Artificial passive immunization typically involves injecting pre-made antibodies, particularly during disease outbreaks or as emergency treatment for toxicity, such as tetanus. Humanized antibodies produced in vitro are preferred over animal-derived antibodies to minimize the risk of anaphylactic shock.