§ It is the exaggerated response of the immune system to certain antigens present in the environment.
§ Allergens: Substances causing allergy. E.g. mites in dust, pollens, animal dander, fur etc.
§ Antibodies produced against the allergens are IgE type.
§ IgE binds on mast cells to release chemicals like histamine and serotonin from them. It results in allergic reactions.
§ Symptoms: Sneezing, watery eyes, running nose, difficulty in breathing, wheezing, skin rashes etc.
§ Determination of cause of allergy: The patient is exposed to or injected with very small doses of possible allergens, and the reactions studied.
§ Treatment: Drugs like anti-histamine, adrenaline and steroids quickly reduce the symptoms of allergy.
§ Asthma is a respiratory disease due to allergy.
§ Modern-day life style and protected environment provided early in life result in low immunity and more sensitivity to allergens. So, many children in metro cities suffer from allergies and asthma.
- In higher vertebrates, memory-based acquired immunity evolved based on the ability to differentiate foreign organisms from self-cells.
- Sometimes, due to genetic and other unknown reasons, the body attacks self-cells resulting in damage to the body. It is called auto-immune disease. E.g. Rheumatoid arthritis.
AIDS (Acquired Immuno Deficiency Syndrome)
§ It is the deficiency of immune system.
§ Syndrome means a group of symptoms.
§ It is caused by HIV (Human Immunodeficiency Virus), a retrovirus having RNA genome.
§ AIDS was first reported in America (1981).
§ In the last 25 years, it killed over 25 million persons.
§ Sexual contact with infected person.
§ Transfusion of contaminated blood & blood products.
§ Sharing of infected needles.
§ From infected mother to her child through placenta.
High risk people of getting HIV:
§ Individuals with multiple sexual partners.
§ Drug addicts who take drugs intravenously.
§ Individuals who require repeated blood transfusion.
§ Children born to an HIV infected mother.
HIV does not spread by touch or physical contact. It spreads only through body fluids.
There is a time-lag (from few months to 5-10 years) between the infection and appearance of symptoms.
Replication of retrovirus:
Life cycle of HIV:
HIV enters body → To macrophages (acts as HIV factory) → RNA genome replicates in presence of Reverse transcriptase to form viral DNA → Viral DNA incorporates into host DNA→ Infected cells produce virus particles → HIV enters into helper T-cells (TH lymphocytes) → Replicates & produce progeny viruses → Attack other TH cells → TH cells decrease → Weaken immunity.
§ During this period, the person suffers from fever, diarrhoea and weight loss.
§ Due to deficiency of TH cells, he may be infected with Mycobacterium, viruses, fungi & parasites like Toxoplasma.
§ Diagnosis: ELISA test (Enzyme-linked immuno-sorbent Assay).
§ Treatment: Anti-retroviral drugs are partially effective. They can only prolong the life of the patient.
Prevention of AIDS:
o Educate people about AIDS through organisations like National AIDS Control Organisation (NACO), non-governmental organisations (NGOs), WHO etc.
o Make blood (from blood banks) safe from HIV.
o Use disposable needles and syringes.
o Advocate safe sex and free distribution of condoms.
o Control drug abuse.
o Regular check-ups for HIV in susceptible population.