Read the given passage and answer the questions that follow:-
The word AIDS means deficiency of immune system acquired during the lifetime of an individual indicating that it is not a congenital disease. AIDS was first reported in 1981 and in the last 25 years it has spread all over the world killing more than 25 million persons. AIDS is caused by the HIV (Human Immuno deficiency Virus). The people who are at high risk of getting this infection includes the individuals who have multiple sexual partners ,drug addicts who take drugs intravenously, individuals who require repeated blood transfusions and children born to an HIV infected mother. It is imperative for the physical and psychological well being that the HIV / AIDS infected persons are not isolated from the family and society. A widely used diagnostic test for AIDS is ELISA.

How does the HIV decrease natural immunity of the body?

Attacking T- Lymphocytes

The correct answer is Option (3) -Attacking T- Lymphocytes

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. This viral DNA gets incorporated into host cell’s DNA and directs the infected cells to produce virus particles . The macrophages continue to produce virus and in this way acts like a HIV factory. Simultaneously, HIV enters into helper T-lymphocytes (T_H), replicates and produce progeny viruses. The progeny viruses released in the blood attack other helper T-lymphocytes. This is repeated leading to a progressive decrease in the number of helper T-lymphocytes in the body of the infected person. 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 that could have been otherwise overcome such as those due to bacteria especially Mycobacterium, viruses, fungi and even parasites like Toxoplasma. The patient becomes so immuno-deficient that he/she is unable to protect himself/herself against these infections.