DISORDERS OF IMMUNE SYSTEM
Hypersensitivity (Allergy)
• Hypersensitivity or allergy is an exaggerated immune response to common antigens, called allergens.
• Allergy is due to the release of chemicals like histamine and serotonin from the mast cells.
• Common examples of allergens are mites in dust, pollens, animal dander, etc.
• Symptoms of allergic reactions include sneezing, watery eyes, running nose and difficulty in breathing.
• The use of drugs such as antihistamines, adrenaline and steroids quickly reduce the symptoms of allergy.
• Common examples of allergy are hay fever and asthma.Autoimmunity
• Autoimmunity refers to abnormal immune responses in which the immune system fails to properly distinguish between self and
non-self and attacks self body proteins.
• When the cells act as antigens in the same body, they are called autoantigens.
• Some of the examples of autoimmune disorders are Grave’s disease, Rheumatic fever, Myasthenia gravis, Pernicious anaemia, etc.Immunodeficiency Diseases
• Immunodeficiencies occur when one or more of the components of the immune system are inactive due to gene mutations,
infections, malnutrition or accident.
• A person suffering from an immunodeficiency disease is liable to suffer from diseases which normally would not occur
(opportunistic diseases).
• SCID and AIDS are two common immunodeficiency diseases.Severe Combined Immuno Deficiency or SCID
• It occurs due to defect in the specialised white blood cells (B and T-cells) that represents a group of rare, sometimes fatal,
congenital disorders characterised by little or no immune response.Acquired Immuno Deficiency Syndrome or AIDS
• AIDS is a disorder of cell-mediated immune system of the body. There is a reduction in the number of helper T cells which
stimulate antibody production by B-cells.
• This results in the loss of natural defence against viral infections.
• The infection by human immuno-deficiency virus (HIV) causes AIDS.
• The incubation period of AIDS ranges between 6 months to 10 years.Infection by HIV
(i) Infection : irusV enters the body of a person and reaches macrophages (cells of immune system).
(ii) Reverse transcription : The viral RNA is converted to viral DNA with the help of reverse transcriptase enzyme.
(iii) Integration : iralV DNA is incorporated into the host cell’s DNA and gets replicated.
(iv) Multiplication : heT viral DNA replicates along with infected host cell. Thus, the infected macrophages act as HIV factory.
(v) Assembly of virus : heT viral proteins formed are
assembled to form new viral particles which are
released from the infected cell. They mature and
target T-cells of body (destroy them).
(vi) Since the number of helper T lymphocytes decrease
in the body, the person becomes susceptible to
infections of bacteria, viruses, fungi and even
parasites like Toxoplasma.
(vii) The patient gets immune deficient and he/she is
unable to protect himself/herself against these
infections.