Immune System Disorders: Autoimmunity & Allergies

Understanding Autoimmunity

An animal's immunological system can typically recognize its own body's molecules and distinguish them from foreign ones, producing antibodies against foreign substances. However, in rare cases, it produces antibodies against the body's own components. This phenomenon is called autoimmunity.

The consequence of this error is the development of serious diseases. Autoimmunity can be caused by genetic factors and may be inherited.

The body's own molecules that trigger autoimmunity are called autoantigens. Certain proteins can act as autoantigens. An autoimmune response occurs when these proteins are released into the bloodstream due to tissue injury.

Biochemical analysis has revealed that many microbes have evolved a strategy of forming proteins very similar to those of the infected animal's body. This is known as molecular mimicry.

Immune System Dysfunctions and Deficiencies

Immunological responses can sometimes become harmful to the organism, inducing damage in various tissues. When the immune system (IS) acts excessively, it is called hypersensitivity. In other cases, defects in immunological mechanisms lead to autoimmune diseases.

Autoimmune Diseases

Most autoimmune diseases or abnormalities affect individuals who have specific types of MHC proteins associated with their cell membranes. In humans, these MHC proteins are called HLA proteins. Certain HLA proteins bind to "mimetic" fragments of germs and present them to T lymphocytes. Consequently, these lymphocytes become unable to distinguish the body's own molecules from the mimicked ones, violating self-tolerance (autotolerance) and leading to autoimmunity.

The best-known autoimmune condition is multiple sclerosis, a non-contagious disease affecting the white matter of the central nervous system. It causes numbness and pain in the legs and arms, abnormal vision, and problems with strength and balance.

Allergies and Hypersensitivity Reactions

A hypersensitivity reaction is an excessive immune system response upon exposure to relatively harmless antigens. An allergen is an antigen that causes hypersensitivity (e.g., pollen from some plants). An allergy is the resulting hypersensitivity reaction.

An animal first subjected to an allergen is considered sensitized or allergic.

Hypersensitivity can cause serious damage and even death; this severe reaction is called anaphylaxis.

There are two main types of hypersensitivity reactions:

• Immediate hypersensitivity reaction: Adverse effects appear within minutes of contact with the allergen.
• Delayed-type hypersensitivity reaction: Effects become noticeable after hours or days.