The immune system can over or underreact to several different agents, leading to disorders in immunity. Such agents include environmental stimulants, like animal dander and pollen, as well as reactions to changes in specific body tissue types. Hypersensitivity reactions are immune system overreactions involving either antibodies or immune cells that result in damage to a person's own tissues. Common allergies to everything from pollen to poison ivy are hypersensitive immune overreactions. Allergies can be serious, with severe hypersensitivity causing a systemic reaction called anaphylaxis that can result in loss of blood circulation, closed airways, and death. Autoimmune diseases are immune disorders that are caused by overreactions triggered by an organism’s own cells.
At A Glance
- Immunopathology is the study of disease states that are associated with overreactivity or underreactivity of the immune response.
- Major categories of B cell–mediated hypersensitivity include type I (common allergy), type II (cytotoxic antibody dependent), and type III (immune complex formation).
Type I hypersensitivity reactions are classified based on the presence of IgE antibodies specific to the causative antigen, eliciting a response in sensitized individuals.
Type II hypersensitivity reactions are characterized by an immune response against a specific tissue type.
Type III hypersensitivity reactions are characterized by the formation and accumulation of antibody-antigen complexes.
- Type IV hypersensitivity reactions are not mediated by antibodies, but instead represent a delayed hypersensitivity mediated by T cells that release cytokines and draw macrophages to the site.
Anaphylaxis is a systemic reaction that involves airway obstruction and circulatory collapse and can be fatal.
Diagnosis of allergies involves several different levels of testing that can include nonspecific, specific, in vitro, and in vivo methods.
Hemolytic disease of the newborn occurs when a mother has developed antibodies against antigens displayed on the surface of a fetus's red blood cells.
- Autoimmune disease is a result of overproduction of autoantibodies. This can occur from genetic irregularities or errors in the immunologic processes.