(i) Use of safe blood for transfusion
(ii) Use of disposable needles
(iii) Prevention of drug abuse
(iv) Advocating safe sex

(i) In the 195"os,experiments by Porter and Edelman revealed the basic structure of the immunoglobulin.
(ii) An antibody molecule is Y shaped structu re that comprises of four polypeptide chains, two identical light chains (L) of molecular weight 25,000 Da (approximately 214 amino acids) and two identical heavy chains (H) of molecular weight 50,000 Da (approximately 450 amino acids).
(iii) The polypeptide chains are linked together by di-sulphide (S-S) bonds. One light chain is attached to each heavy chain and two heavy chains are attached to each other to form a Y shaped (Fig.) structure. Hence, an antibody is represented by H₂L₂.
(iv) Each chain (L and H) has two terminals. They are C - terminal (Carboxyl) and amino or N-terminal.
(v) Each chain (L and H) has two regions. They have variable (V) region at one end and a much larger constant (C) region at the other end.
(vi) Antibodies responding to different antigens have very different (V) regions but their (C) regions are the same in all antibodies.
(vii) In each arm of the monomer antibody, the (V) regions of the heavy and light chains combines to form an antigen - binding site shaped to 'fit' a specific antigenic determinant. Thus each antibody monomer has two such antigen - binding regions.
(viii) The (C) regions that forms the stem of the antibody monomer determine the antibody class and serve common functions in all antibodies.

Porter and Edelman revealed the basic structure of the immunoglobulin. An antibody molecule is Y shaped structure that comprises of four polypeptide chains, two identical light chains (L) of molecular weight 25,000 Da (approximately 214 amino acids) and two identical heavy chains (H) of molecular weight 50,000 Da (approximately 450 amino acids). The polypeptide chains are linked together by di-sulphide (S-S) bonds. One light chain is attached to each heavy chain and two heavy chains are attached to each other to form a Y shaped structure. Hence, an antibody is represented by H₂ L₂.

(i) After getting into the body of the person, the virus enters into macrophages where RNA genome of the virus replicates to form viral DNA with the help of the enzyme reverse transcriptase.
(ii) This viral DNA gets incorporated into the DNA of host cells and directs the infected cells to produce viral particles.
(iii) The macrophages continue to produce virus and in this way acts like a HIV factory.
(iv) Simultaneously, HIV enters into helper T-Iymphocytes, replicates and produces progeny viruses. The progeny viruses released in the blood attack other helper T-lymphocytes. The process is repeated.
(v) During this period, the person suffers from bouts of fever, diarrhoea and weight loss. Due to decrease in the number of helper T lymphocytes, the person starts suffering from infections and becomes immune deficient and unabie to protect against any infection.

B and T cells are the two type of lymphocytes. Both are produced in the bone marrow.

S.No	B lymphocytes (B cells)	T lymphocytes(T cells)
i.	They stay in the bone marrow until they are mature.	T lymphocytes leave the bone marrow and mature in the thymus gland.
ii.	B cells can bind with antigens and produce antibodies or become memory cells.	T cells do not produce antibodies. They recognize antigen cells and destroy them presenting.
iii.	It is not classified into different types.	T cells are of two types. Helper T cells and KillerT cells.

S.No	Autoimmune disease	Immunodeficiency disease
i.	If the immune system of the body fails to distinguish foreign molecules from self, then it reacts destructively against the host's own molecules. This is known as autoimmune disease.	An immunodeficiency disease results from the failure of one or more components of the immune system which could be due to genetic reasons, radiation, infections etc.,
ii.	Eg: Multiple sclerosis is a autoimmune disease	Eg: AIDS is a Immunodeficiency disease.

S.No	Humoral Immunity	Cell mediated immunity
i.	When Pathogens are destroyed by the production of antibodies, it is known as antibody mediated or hurmoral immunity.	When Pathogens are destroyed by cells without producing antibodies it is known as cell mediated immunity.
ii.	This is brought about by B cells with the aid of antigen presenting cells and T helper cells.	This is brought about by T cells, macrophages and natural killer cells

S.No Active immunity passive immunity i. Active immunity is produced actively by host's
immune system. Passive immunity is received passively and there
is no active host participation. ii. It is produced due to contact with pathogen or by
its antigen. It is produced due to anti-bodies obtained from
outside. iii. lt is durable and effective in protection. It is transient and less effective. iv. Immunological memory is present. No memory. v. Booster effect on subsequent dose is possible. Subsequent dose is less effective. vii. Immunity is effective only after a short period Immunity develops immediately.

S.No	Primary immune responses	secondary immune responses
i.	It occurs as a result of primary contact with an antigen.	It occurs as a result of second and subsequent contacts with the same antigen.
ii.	Antibody level reaches peak in 7 to 10 days	Antibody level reaches peak in 3 to 5 days.
iii.	Prolonged period isrequired to establish immunity	It establishes immunity in a short time.
iv.	There is rapid decline in antibody level.	Antibody level remains high for longer period.
v.	It appears mainly in the lymph nodes and spleen.	It, appears mainly in the bone marrow followed by the spleen and lymph nodes.

S.No	Innate Immunity	Acquired Immunity
i.	Innate Immunity is the natural phenomenon of resistance to infection which an individual possesses right from birth.	The immunity that an individual acquires after birth is known as acquired immunity.
ii.	The innate defense mechanisms are non-specific and are effective against a wide range of infectious agents.	The unique features of acquired immunity are antigenic specificity, diversity, recognition of self and non-self and immunological memory
iii.	Innate Immunity comprises of anatomicalphysiological, phagocytic and inflammatory barriers.	It has two components cell mediated immunity and antibody mediated immunity.