(i) They are glands located in the roof of the mouth.
(ii) They produce antibodies that help to fight infections.
(iii) The adenoids shrink during adolescence and disappear later.

Lymph nodes, appendix, peyer's patches of gastrointestinal tract, tonsils, adenoids, spleen are examples of secondary lymphoid organs.

Bursa of Fabricius of birds, bone marrow and thymus gland of mammals are the primary lymphoid organs.

Normal cells show a property called contact inhibition, which inhibits uncontrolled growth. Cancer cells do not have this property. As a result, cancerous cells divide continuously giving rise to mass of tissues called tumours.

ELISA - Enzyme Linked Immunosorbent Assay. It is a preliminary test which detects the presence of HIV antibodies.

H[V - Human Irnmuno Deficiency Virus
AIDS - Acquired Imrnu no Deficiency Syndrome.

A vaccine is a biological preparation that provides active acquired immunity to a particular disease and resembles a disease causing microorganism and is often made from weakened or attenuated or killed forms of the microbes, their toxins, or one of its surface proteins.

The binding force between antigen and antibody is due to three factors. They are
(i) closeness between antigen and antibody
(ii) non-covalent bonds or intermolecular forces and
(iii) affinity of antibody.

Antibodies are classified into five major categories based an physiological and biochemical properties. They are IgG (gamma), IgM (rnu), IgA (alpha), IgD (delta) and IgE (epsilon).

The process of production of blood cells in the bone marrow is called haematopoiesis.

MALT stands for Mucosa - Associated Lymphoid Tissue.
BALT stands for Bronchial / Tracheal - Associated Lymphoid Tissue.
These are the examples of secondary lymphoid organs.

The immunity that an individual acquires after birth is known as acquired immunity. It is the body's resistance to a specific pathogen.

Inflammatory barriers is a type of Innate Immunity. Tissue damage and infection induce leakage of vascular fluid, containing chemotactic signals like serotonin, histamine and prostaglandins.

Interferons are a group of signalling proteins produced by virus infected cells. They interfere with viral replication and hence named interferons. A virus infected cell releases interferons which induce antiviral state in the uninfected cells. They are chemical mediators under physiological barriers offering Innate immunity.

The immune responses may be primary or secondary.
(i) The primary immune response occurs when a pathogen comes in contact with the immune system for the first time.
(ii) The secondary immune response occurs when a person is exposed to the same antigen again. During this time, immunological memory has been established and the immune system can start producing antibodies immediately. Within hours after recognition of the antigen, a new army of plasma cells are generated. Within 2 to 3 days, the antibody concentration in the blood rises steeply to reach much higher level than primary response. This is also called as "booster response".