12th Zoology

Immune system disorders

Immune system disorders

The immune system is a multicomponent interactive system. It
effectively protects the host from various infections. But an improper
functioning of the immune system can cause discomfort, disease or even death.
The improper functions fall into the following major groups :
(1) hypersensitivity or allergy, (2) auto-immune diseases, and
(3) immunodeficiency. (Immune system disorders)


Allergies result from an inappropriate and excessive immune response
to common antigens. Substances that cause allergies are called allergens ;
they include dust, moulds, pollen, certain foods, and some medicines (such
as penicillin). Allergy involves mainly IgE antibodies and histamine. Mast cells
secrete the histamine. A common manifestation of allergy is asthma. Sometimes
an allergen may cause a sudden, violent and fatal reaction in a sensititive
individual ; this is called anaphylaxis. (Immune system disorders)

Autoimmune diseases

Autoimmune diseases result when the immune system attacks and
destroys “self” cells and molecules. This condition can cause chronic and
serious diseases. Examples of autoimmune diseases are insulin-dependent
diabetes, multiple sclerosis, rheumatoid arthritis, etc. Multiple sclerosis is
caused by antibodies that attack the myelin sheath of nerve cells. (Immune system disorders)

Immunodeficiency diseases

Immunodeficiency Diseases result from a defect in one or more
components of the innate or adaptive immunity. Affected individuals are
susceptible to diseases that normally would not bother most people.
Immunodeficiency may result from gene mutations, infections, malnutrition
or accidents. (Immune system disorders)

a. Severe combined immunodeficiency (SCID) results from one of many
genetic defects; one such genetic defect leads to adenosine deaminase
deficiency. SCID is characterized by a very low number of
circulating thymocytes. Affected individuals usually die at an early age.

b. AIDS (Acquired Immuno Deficiency Syndrome) is another example for
immunodeficiency disease. It is caused by a retrovirus, known as human
immunodeficiency virus (HIV). Retroviruses have RNA genomes that are
replicated via DNA copies. HIV, selectively infects and kills T-helper cells.
The depletion of T-helper cells weakens the acquired immune response and
may even abolish it completely. The viral RNA genome is converted into
DNA copy by the viral enzyme reverse transcriptase. The DNA copy of
HIV becomes inserted into the human chromosome and replicates with the
cell DNA. It may be transcribed to produce RNA copies of the viral genome.
The RNA copies are packaged and liberated as virus particles. The infected
cell is lysed in this process, and the released virus particles infect new Thelper
cells. (Immune system disorders)

Related Topics in Zoology:

Bio Zoology All Important Topics

  1. Microbiology Introduction and History of Medical Microbiology

  2. Pasteur, Koch, Lister

  3. Structure of Viruses

  4. Viral genetics

  5. Virus Culture

  6. Viral Diseases

  7. Bacteria Structure Culture

  8. Bacterial Genetics

  9. Bacterial Diseases

  10. Protozoan microbiology

  11. Pathogenecity of Microorganisms

  12. Antimicrobial Resistance

  13. Antibiotics and Chemotherapy

  14. AIDS – HIV

Unit 3 – Immunology Topic List Zoology


  2. Acquired Immunity

  3. Structure and Functions of the Immune System

  4. Peripheral Lymphoid Organs

  5. Secondary Lymphoid Organs

  6. Antigenic determinants and epitopes

  7. Antibodies – Immunoglobulins

  8. Transplantation immunology

  9. Genetic basis of organ transplants

  10. Immune system disorders

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