Immune System Defense Mechanisms: Barriers, Immunity and Inflammation

Defense Mechanisms (Barriers)

Non-Specific Barriers

Cognitive sense: NK cells are not specific and do not discriminate between agents, and they are not pathognomonic. Memory is not needed; they do not recognize antigens and do not get reinforced after the first infection.

The Skin

The skin is both the first barrier: mechanical and chemical. The chemical function of the barrier depends on two glands: sebaceous and sudoriferous. These two secretions give the skin a pH that is slightly acidic, which is very effective against germs. Against any external agent, for example Staphylococci, acne.

Mucosal Membranes

Mucous membranes are soft, highly vascular tissue covering any surface or internal cavity. The mucous secretion prevents the binding of bacteria. The mucus contains lysozyme (an enzyme) that has a bactericidal action.

Body Fluids

Body fluids (corporal fluids) such as saliva and tears contain enzymes with bactericidal function. Lactoferrin is an enzyme that acts together with the first line of defense.

Bacterial Flora

Some bacteria live symbiotically with us, and we both benefit. They function by competing for the same resources as pathogenic bacteria, for example Candida.

Non-Specific Cells

Phagocytic cells: Macrophages are cells that originate in the bone marrow, like any blood cell. They can leave blood vessels and move through tissues. They have three basic functions:

• They remove debris from any tissue, for example by absorbing pus.
• They detect antigens and mark them so they can be accessed by antibodies.
• They trigger immune responses and inflammatory reactions.

The Inflammatory Response

When tissue is broken and there is continuous external bleeding, the response is immediate. Blood circulation increases with the objective of carrying blood plasma, white blood cells and antibodies to the site, to stop the bleeding and prevent the entry of pathogens.

Any pain is caused by overstimulation of nerve terminals by prostaglandins. Prostaglandins also cause fever (pyrogens). Macrophages release pyrogenic substances that travel through the blood to the brain and stimulate the hypothalamus, which controls body temperature. The fever mechanism is a defense. Vasodilation is caused by histamine, which is an allergy-causing substance.

Tissue damage releases histamine, which causes vasodilation.

Specific Defenses (Immunity)

Immunity: We are immune when immune antibodies are present that recognize specific antigens.

Types of Immunity

Active Immunity

The body produces its own antibodies, and it can be acquired in two ways:

• Artificial: A vaccine is supplied, and it stimulates the production of antibodies. Vaccines contain antigens that are dead or weakened, or non-toxic, causing an immune response.
• Natural: The person suffers the disease.

Passive Immunity

Antibodies are received from outside the body, and it can be acquired in two ways:

• Artificial: The patient is given serum containing specific antibodies, such as an antidote.
• Natural: The mother transfers antibodies through the placenta or breast milk, which protect the child for a limited time. This is reinforced with breastfeeding.

Antigens and Antibodies

Antigen: Can be of biotic or abiotic origin. Large molecules always trigger an immune response in the host organism.

Antibody: Also called immunoglobulins, these are proteins of the immunoglobulin family. They are tertiary or depending on the humoral defense, and they are the most effective of all defensive barriers. They are specific to individual antigens.

Interplay Between Antibodies and Antigens

• Agglutination: Antibodies bind to antigens, forming clumps that can be accessed by macrophages. For example, hemagglutination occurs when blood types are incompatible.
• Neutralization: Affects especially viruses and bacteria, consisting of preventing the bacteria or virus from spreading.
• Opsonization: In this case, the antigen becomes a toxin or toxoid.

Autoimmunity

Autoimmunity is a disorder of genetic origin. The individual suffers an attack of their own defenses against their own tissues. It can be mitigated by immunosuppression, corticosteroid treatment, reducing the body's immune response, or by transplant.

Examples include systemic lupus erythematosus and pernicious anemia.

Immunodeficiency

There are disorders or acquired organic causes, for example AIDS, and others such as transplant rejection. It shows a decrease in the individual's defenses.

Allergy

Hypersensitivity to antigens that are normally harmless. It is the response to a violent reaction in an individual. It is usually localized, but when it runs throughout the body it can cause anaphylactic shock.

Rejection

The immune response to a transplanted tissue from another person.