Immunity: its types and how it works

Immunity (from the Latin "immunitas" - "deliverance") is a complex system of protection of the body against infections, diseases and other external influences. It is a set of biological mechanisms that can recognize and fight pathogens, such as bacteria, viruses, fungi, parasites, and even abnormal (cancerous) cells inside the body.

Immunity can be natural (innate) and adaptive (acquired).

History of the discovery of the immune system

• Ancient medical texts, such as Ebers Papyrus (circa 1550 BC), already mention methods for preventing and treating infections. However, the concept of immunity as we understand it today had not been developed.
• In the early 18th century, the English physician Edward Jenner first introduced the idea of vaccination as a way to prevent infections. He created a smallpox vaccine using vaccinated material from a cow (cowpox), and this was the first ever use of artificial immunization.
• Cellular and humoral immunity. In the 19th century, scientists Ilya Mechnikov and Louis Pasteur contributed to the study of immunity. Mechnikov developed the concept of phagocytosis (the process of absorption of bacteria and other particles by immune system cells), and Pasteur proposed the theory of humoral immunity, pointing to the role of antibodies in fighting infections.

• In the early 20th century, German immunologist Paul Ehrlich made a significant contribution to the study of antibodies. He coined the term "antibodies" and developed the idea of the specificity of antibodies in the fight against infections.
• With the discovery of T and B lymphocytes, American scientists Macfarlane Burnet and Peter Meadows put forward the concept of cellular and humoral immunity and proposed the idea of the coexistence of T lymphocytes and B lymphocytes that interact to provide adaptive immune defense.
• In the second half of the 20th century, with the development of molecular biology and genetics, molecules and genes responsible for the functioning of the immune system were identified and described, including genes encoding antibodies and immune system cells.

Innate immunity is the body's primary defense system against infections and other external threats. It is genetically inherited and is present in the body from birth. Innate immunity is not specific to specific pathogens and affects a wide range of microorganisms, detecting common molecules characteristic of bacteria and viruses.

Components of innate immunity include:

• Skin and organ mucous membranes are physical barriers that prevent microorganisms from entering the body.
• Phagocytes, such as neutrophils and macrophages, are white blood cells that can absorb and destroy pathogens.
• Inflammation is the body's response to infection or injury, which includes increased vascular permeability and the migration of phagocytes to the site of inflammation.
• Complement proteins, proteins that can be activated in response to infection and contribute to the destruction of microorganisms.
• Interferons are molecules that help limit the spread of viruses in the body.

Innate immunity responds quickly to pathogens, but its action is not specific, and it does not create immunological memory. This means that it cannot provide long-term protection against specific infections, as adaptive immunity does. However, innate and adaptive immunity work closely together to ensure that the body is fully protected.

Adaptive immunity develops in response to specific pathogens and allows the body to "remember" them and fight them more effectively in the future. Acquired immunity (or adaptive immunity) is the second level of the body's defense against infections and other external threats. Adaptive immunity develops in response to specific pathogens and is stable, which means that it attacks certain microorganisms and antigens (characteristic molecules of pathogens).

Characteristics of adaptive immunity:

• Adaptive immunity can recognize and attack specific pathogens or antigens. It creates antibodies and T-lymphocytes that are directed against specific microorganisms.
• Immunological memory has the ability to "remember" pathogens that the body has encountered before. This means that when the body is exposed to the same pathogen again, it is able to react faster and more effectively, providing stronger protection.

• Provides long-term protection against infections.
• It develops as a result of exposure to infections, vaccination, or contact with antigens. It includes cells that produce antibodies and T-lymphocytes that play a role in the cellular immune response.
• It is slower and more specific than innate immunity, but it is a powerful defense against specific infections and plays a key role in the body's long-term protection against disease.

Cellular immunity is one of the main components of adaptive immunity, which depends on the action of various cells of the immune system, especially T-lymphocytes. Cellular immunity is aimed at destroying infected cells, tumor cells, and other abnormal cells in the body.

The main elements of cellular immunity:

T-lymphocytes

• These are cells of the immune system that specifically recognize antigens on the surface of infected or altered cells and can attack and destroy such cells, playing an important role in protecting the body from viral infections, tumors, and other threats.

Cytotoxic T lymphocytes (killer cells)

• CTLs are a subtype of T lymphocytes that can directly harm infected cells by destroying them.

T-helper cells (helpers)

• T-lymphocytes play a role in regulating and activating other cells of the immune system, helping them fight infections.

T regulators (suppressors)

• T regulators control the immune response and prevent autoimmune reactions when the immune system attacks the body's own tissues.

Cellular immunity is effective in the fight against viruses, bacteria, fungal infections, and certain types of tumors, and is involved in tissue regeneration and repair. This type of immunity works in conjunction with humoral immunity, which includes antibodies and B lymphocytes. Both components of adaptive immunity interact to provide complete and specific protection of the body against various threats.

Humoral immunity is one of the two main components of adaptive (acquired) immunity and deals with antibodies and B-lymphocyte cells that circulate in body fluids such as blood, lymph, and mucous membranes.

Characteristics of humoral immunity:

• Antibodies (immunoglobulins) are proteins that are produced by B-lymphocytes in response to antigens (characteristic molecules of pathogens). Antibodies are able to bind to antigens and block their effects, as well as enhance the destruction of pathogens.
• B-lymphocytes play a role in the production and secretion of antibodies. They undergo activation and differentiation to become plasma cells that release antibodies into the bloodstream.
• Humoral immunity is involved in the regulation of the inflammatory process and adapts the immune response depending on the type of infection.

• It is effective in fighting various infections, especially bacterial ones. The antibodies produced by this system can attach to bacteria, making them available to phagocytes (macrophages) that destroy them.
• Humoral immunity works closely with cellular immunity to provide the body with comprehensive and specific protection against infections.

Immunity is not a function of one specific organ but a complex system that includes many organs, tissues, cells, and molecules.

Components of the immune system:

Bone marrow

• This is where the production of immune system cells, such as white blood cells, which play a key role in fighting infections, takes place.

Thymus or thymus gland

• The thymus plays an important role in the development and maturation of T-lymphocytes, one of the types of white blood cells responsible for adaptive immunity.

Spleen

• It performs blood filtration functions and is involved in the destruction of old blood cells and the fight against infections.

Lymphatic system

• Includes lymph nodes and lymphatic vessels and lymph and plays a role in the circulation of lymphocytes and other cells of the immune system.

Organs and tissues

• Many organs and tissues in the body contain immune system cells that perform protective functions, such as macrophages and dendritic cells.

Lymphocytes

• These cells are key components of adaptive immunity, circulating in the body to fight specific infections.

The immune system functions as a whole and different components interact to protect the body from infections. There is no one specific organ that can be called the "immune organ". Instead, the immune system is made up of many parts that interact to provide protection for the body.