Immune Memory and Mechanisms of Acquired Immunity

Immune Memory and Lymphocyte Response

The formation of memory cells of all types of lymphocytes involved in the immune response after initial contact with an antigen (primary immune response) allows the immune response to be much faster during a second contact, even several years after the first (secondary reaction). This can be verified by measuring the dose of antibodies in an organism in both situations.

• Primary immune reaction: Production of antibodies in the IgM form.
• Secondary immune reaction: Faster and wider production of antibodies in the IgG form.

Types of Immunity

Immunity is the protection against infectious agents. An organism is considered immune to an antigen when it is able to destroy or deactivate it without suffering from any disease. In mammals, such immunity can be obtained naturally or by artificial means.

Natural Immunity

• Active: Based on immunological memory that is acquired after an initial contact with a pathogen and can be maintained for many years.
• Passive: Acquired during embryonic development; the newborn is protected for about six months against many pathogenic microorganisms while their immune system develops fully.

Artificial Immunity

• Active: Achieved through vaccines, which contain the pathogen or toxin. Immunity is developed against that particular pathogen. Vaccination is used for disease prevention and involves vaccinating the entire population. This has totally eradicated diseases like smallpox. Some microorganisms are inoculated dead, while in other cases, the toxin produced by the pathogen is used. Vaccines against many viral diseases use attenuated viruses.
• Passive: Achieved through serum therapy. A serum contains specific antibodies against a certain disease made by another body. It is typically used when an individual has contracted a disease and needs antibodies immediately. Its effects are not lasting because the body does not start its own response and has not produced memory cells.

Serum Production and Immunoglobulins

Sera were historically obtained from animals (such as horses) previously infected with the pathogen. They were injected to respond by synthesizing large amounts of antibodies to pass into the blood. This blood was extracted and filtered to obtain the serum. Today, immunoglobulins are available against many pathogenic microorganisms and toxins, such as certain snake venoms.