Understanding the Body's Immune System and Immunity

Mechanisms of Defense: The Immune System

The immune system consists of a set of organs, cells, and molecules dispersed throughout the body that is responsible for its defense. This defense system operates through internal and external defenses.

External Defenses

They consist of physical and chemical barriers and are the first line of defense to prevent the entry of pathogens. These barriers are mainly the skin and mucous membranes.

Internal Defenses

In the interior of the body, we can distinguish two types of defenses:

• Nonspecific Defenses

  Are so called because they do not depend on the nature of the pathogen. The most important are the inflammatory reaction and the nonspecific cellular defense:

  • Inflammatory reaction. It is a local reaction involving the connective tissue and blood vessels, which aims to isolate and destroy microorganisms.

  • Nonspecific Cellular Defense

    It is carried out by macrophages, neutrophils, and other cells that are capable of phagocytosing and destroying microorganisms.

• Specific Cellular Defense

  They are based on specific recognition of antigens.

Antigens are foreign molecules recognized by the body, against which a specific immune response is triggered.

Triggering the immune response, antigens may be mediated by cells that directly attack the invading antigen, or by antibodies, which are proteins produced by a type of lymphocyte, the B cell, and which may remain attached to the plasma membrane or circulate in blood plasma. The antibodies bind to specific antigens.

Another property of the immune response is memory: After a first contact with a specific antigen, a primary immune response is produced in which some cells acquire memory. Upon a second encounter with the same antigen, a secondary immune response is triggered, much more efficient and faster than the primary response. This is the basis of vaccination.

Immunity and Immunization: Vaccines

Immunity is a state of defense and resistance, i.e., protection against a disease, provided by the immune system. We can distinguish two types of immunity: natural immunity and artificial immunity or immunization.

Natural Immunity

It is a type of immunity that is acquired as a result of the normal functioning of the immune system. It can be passive or active.

• Passive Natural Immunity

  It originates from the presence of antibodies in the body before exposure to the antigen. These antibodies are provided by the mother to the fetus through the placenta and to the newborn during lactation.

• Active Natural Immunity

  Is obtained after contact with a pathogen that triggers a specific immune response, resulting in memory against the pathogen. Once the disease is overcome, immunity is also acquired to the same, like measles, a typical infectious disease of childhood.

Artificial Immunity

Immunization is a medical procedure that aims to increase the effectiveness of the body's immune response against infectious diseases. There are two types of immunization: active and passive:

• Active Immunization or Vaccination

  It is the induction of immunity by injection of attenuated or dead microorganisms or their components or products. Vaccination results in a primary response in which some cells acquire memory. If the body is again exposed to the same antigen, a secondary response will occur much more quickly and efficiently.

  A vaccine is material prepared from dead or attenuated organisms or their components or products, which can trigger an immune response in the body.

• Passive Immunization

  Involves injecting specific antibodies that can neutralize toxic substances (called toxins) produced by microorganisms, such as the tetanus or diphtheria toxin. It is also an effective procedure against substances like snake venoms.