Immunopathology
Immunopathology is a specialized area within immunology that focuses on diseases caused by the immune system, encompassing four primary categories: autoimmune disorders, congenital immunodeficiencies, acquired immunodeficiencies, and hypersensitivity reactions. Autoimmune disorders occur when the immune system mistakenly attacks the body’s own tissues, leading to conditions like multiple sclerosis and lupus. Congenital immunodeficiencies are genetic conditions present at birth where the immune system is underdeveloped or dysfunctional, such as in DiGeorge syndrome. Acquired immunodeficiencies, on the other hand, develop later in life due to various factors, including infections like HIV, malnutrition, or environmental damage.
Hypersensitivity reactions involve an overactive immune response, leading to allergic reactions or other serious conditions. Treatments for these immune-related disorders vary widely and aim to restore balance to the immune system. Approaches may include immunosuppressive medications, preventive antibiotics, or even bone marrow transplants, depending on the specific condition. As the field of immunopathology continues to evolve, innovations such as gene therapy and advanced vaccines show promise for more effective treatment options in the future. Understanding these conditions and their treatments can help individuals manage their health and seek appropriate medical care.
Immunopathology
Anatomy or system affected: All
Definition: The study of disease processes that have an immunological basis or pathogenesis involving either B cells (antibodies) and complement or T cells, including damage to tissues and cells caused by hypersensitivity reactions.
Science and Profession
Immunopathology is the subdiscipline of immunology that deals with the four basic types of pathologies caused by the immune system: autoimmune disorders, congenital immunodeficiencies, acquired immunodeficiencies, and hypersensitivity reactions. Physicians who deal with such disorders are trained in immunology and/or pathology.
Autoimmune disorders are those in which the body fails to distinguish between self and nonself, leading to an attack by the immune system on the tissues or organs of the body. There are many autoimmune disorders, and the symptoms are extremely varied, depending on the site and extent of the attack. Some disorders are tissue-specific, while others affect tissues and organs throughout the body. Examples of autoimmune disorders are multiple sclerosis (MS), systemiclupus erythematosus (SLE), and myasthenia gravis.
Congenital (primary) immunodeficiencies are those conditions in which there is an absence or a failure of the immune system at birth. Often, they are the result of a failure of one or more components of the immune system to develop during the fetal stages. Most congenital deficiencies have a genetic basis. An example of a primary immunodeficiency disorder is DiGeorge syndrome, in which T cells are deficient as a result of a developmental problem of the thymus. The most severe of these disorders is severe combined immunodeficiency disorder (SCID), in which both B and T cells do not develop or function properly. Complement deficiencies fall into this category as well. Complement is a series of proteins that combine to generate an attack on invading cells, such as bacteria.
Acquired (secondary) immunodeficiencies are those that arise later in life, following a change in some environmental condition or exposure, such as accidents or surgery that damages or removes the spleen or lymph nodes, radiation exposure that damages the bone marrow, and cancers that attack or destroy parts of the immune system. Lymphocytic leukemias (malignancies of bone marrow precursors of B and T cells) are an example of acquired immune system diseases. Malnutrition or the use of certain drugs (especially opiates) may also affect the immune system responses in a negative way. Finally, viruses, such as human immunodeficiency virus (HIV), can attack and suppress the human immune system components, leading to a deficient ability to defend the body from daily attack by microorganisms. Some acquired immunodeficiencies occur without an identified cause.
In contrast to the immunodeficiency syndromes, hypersensitivity reactions are those in which the immune system overreacts in its attempt to keep the body healthy, and, by doing so, causes localized or systemic reactions that can range from annoying to life-threatening. Hypersensitivity reactions are classified according to their molecular mechanism of action and may overlap with other categories, such as autoimmune disorders. Type I reactions are those which most people would recognize as allergies. Here, a series of chemicals, including immunoglobulin E (IgE), are released into the bloodstream, triggering the effects commonly associated with allergies: runny nose, itchy eyes, and difficulty breathing. The most severe case is anaphylaxis, sometimes seen in individuals with allergies to bee or wasp venom or to certain food substances. Type II reactions are those in which existing antibodies in the bloodstream bind to antigens that are seen as foreign and begin the process of tissue destruction. Examples include transfusion reactions, in which the wrong blood type is given to an individual, and erythroblastosis fetalis (hemolytic disease of the newborn), in which maternal antibodies attack a developing fetus that has a different set of antigens. Type III disorders are those in which large immune complexes form and are deposited in the bloodstream or kidneys, leading to disorders such as vasculitis and glomerulonephritis. Type IV reactions are those involving T-cell attack; they include contact dermatitis (such as poison ivy reactions) and transplant rejection.
Diagnostic and Treatment Techniques
Specialists who deal with immunopathologies may provide treatments that vary widely, as do the disorders themselves. The goal of all therapy is to restore the immune system to its normal balance so that it can continue to protect the body from the constant barrage of invading microorganisms. Individuals with immune system deficiencies are told to avoid contact with other individuals as much as possible, since most viruses and bacteria are spread through personal contact. Prophylactic regimens of antibiotics, antivirals, and antifungals are helpful in most of those with immunodeficiencies, but in those with more severe forms, bone marrow transplants are the treatment of choice. The use of passive immunization—transferring antibodies from healthy individuals into those with immunodeficiencies—is helpful in some cases. In acquired immunodeficiency syndrome (AIDS), drug combinations, or “cocktails,” are aimed at suppressing replication of HIV, which attacks the T cells and keeps them from functioning.
Because most hypersensitivity reactions are temporary immunopathologies, their treatment involves short-term therapies to restore balance to the system. Antihistamines, for instance, help many allergy sufferers, as do air purifiers and lifestyle changes. Careful tissue and blood typing can eliminate or lower the instances of the other types of hypersensitivities.
Treatment for autoimmune disorders is also quite variable because of the wide variety of manifestations and underlying causes. Treatments commonly include immunosuppressive drugs and replacement of hormones or other chemicals that the body is lacking.
Perspective and Prospects
Since immunology itself is a field that is still in its infancy, recognition of immune disorders and their treatments is relatively new. Autoimmunity was first described by Paul Ehrlich at the turn of the twentieth century, and he called the phenomenon “horror autotoxicus,” a name that struck fear in patients and providers alike. Hypersensitivity reactions, especially allergies, were recognized hundreds of years ago, and various chemical prescriptions were used to control the symptoms, but it was not until the mid-twentieth century that the molecular basis of allergies began to be understood. Immunodeficiencies are still being described, and the understanding of their basis is quite incomplete.
Some immunodeficiencies, if detected early enough, may be candidates for future gene therapy. In those cases where a single gene defect can be identified, the introduction of the functional gene into the developing tissue may be able to reverse the course of the disease, partially or completely. Other options include transplantation of the thymus or bone marrow in order to allow normal functioning of the immune system components.
One of the most exciting potential treatments for secondary immunodeficiencies is vaccination. The ability to block AIDS through early immunization looked promising but was yet to be a reality in the early 2020s. However, pre-exposure prophylaxis, or PrEP, was commonly prescribed in the early 2020s to prevent HIV transmission and was 99 percent effective.
Bibliography
Abbas, Abul K., Andrew H. Lichtman, and Shiv Pillai. Basic Immunology: Functions and Disorders of the Immune System. 7th ed., Saunders/Elsevier, 2023.
Clark, William R. In Defense of Self: How the Immune System Really Works. Oxford University Press, 2007.
Fischer, A. M., et al. “Naturally Occurring Primary Deficiencies of the Immune System.” Annual Review of Immunology, vol. 15, 1997, pp. 93–124.
Janeway, Charles A.. Immunobiology: The Immune System in Health and Disease. 7th ed., Garland Science, 2007.
Majno, Guido, and Isabelle Joris. "Part III: Immunopathology." Cells, Tissues, and Disease: Principles of General Pathology. 2nd ed., Oxford University Press, 2004.
MedlinePlus. "Immune System and Disorders." MedlinePlus, 17 Aug. 2020, medlineplus.gov/immunesystemanddisorders.html. Accessed 25 July 2023.
National Institute of Allergy and Infectious Diseases. "Immune System." NIH National Institute of Allergy and Infectious Diseases, July 30, 2013.