Immunotherapy also called biological therapy uses substances made by the body or in a laboratory (monoclonal antibodies) to improve or to resist the immune system function. Different approaches have been attempted in the immunotherapy of cancer.

It is an enzyme present in HIV and once the virus enters the macrophages of the host, the RNA genome of the virus replicates to form viral DNA with the help of the Enzyme Reverse transcriptase. Thus the host cells act as HIV factory and produce more progeny viruses.

Routes of HIV transmission include unsafe sexual contact, blood-contaminated needles, organ transplants, blood transfusion and vertical transmission from HIV infected mother to child. HIV is not transmitted by insects or by casual contact.

(i) Whenever a particulate antigen interacts with its antibody, it would result in clumping or agglutination of-the particulate antigen, which is called agglutination reaction.
(ii) The antibody involved in bringing about agglutination reaction is called agglutinin.

a) Determine blood groups for transfusion.
b) determine the characteristics of certain Immunodeficiency diseases.
c) detect the presence or absence of protein in serum.

Antibodies responding to different antigens have very different (V) regions because the (V) regions of the heavy and light chains in each arm of the antibody structure combine to form the antigen binding site shaped to 'fit' a specific antigenic determinant.

The tumor cells spread to other parts of the body from the tumour and give rise to secondary tumour. This is known as metastasis.

(i) On the basis of origin, antigens are classified into exogenous antigens and endogenous antigens.
(ii) The antigens. which enter the host from the butside in the form of microorganisms, pollens, drugs, or pollutants are called exogenous antigens. The antigens which
are formed within the individual are endogenous antigens. Eg. Blood group antigens.

Spleen is a secondary lymphoid organ located in the upper part of the abdominal cavity close to the diaphragm. Spleen contains Band T cells. It brings humoral and cell mediated immunity.

Bursa of fabricius is a primary lymphoid organ of birds. It is attached to the dorsal side of the cloaca. B lymphocytes mature in the bursa and bring about humoral immunity.

Based on their functions, lymphoid organs are classified into primary or central lymphoid organs and secondary or peripheral lymphoid organs.
(i) The primary lymphoid organs provide appropriate environment for lymphocytic maturation. Eg. Thymus gland.
(ii) The secondary lymphoid organs trap antigens and make it available for mature lymphocytes, which can effectively fight against these antigens. Eg. Spleen.

The two types of acquired immunity are active immunity & passive immunity.