What is the mechanism by which the AIDS virus causes deficiency of immune system of the infected person?
AIDS is caused by the Human Immuno deficiency Virus (HIV), a member of a group of viruses called retrovirus, which has an envelope enclosing the RNA genome.
After entering the body of the person, the virus enters into macrophages where the RNA genome of the virus replicates to form viral DNA with the help of the enzyme reverse transcriptase. This viral DNA gets incorporated into the host cell's DNA and directs the infected cells to produce virus particles. The macrophages continue to produce virus and in this way act like a HIV factory.
Simultaneously, HIV enters into helper T-lymphocytes (T_H), replicates and produces progeny viruses. The progeny viruses released in the blood attack other helper T-lymphocytes. This process is repeated leading to a progressive decrease in the number of helper T-lymphocytes in the body of the infected person.
Due to the 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. During this period, the person suffers from bouts of fever, diarrhoea and weight loss.
The patient becomes so immuno-deficient that he/she is unable to protect himself/herself against these infections. Treatment with anti-retroviral drugs is only partially effective and can only prolong the life of the patient but cannot prevent death.
Explanation
The answer draws directly from the NCERT textbook context which explains the complete mechanism of HIV infection: (1) HIV entering macrophages and using reverse transcriptase to convert RNA to viral DNA, (2) incorporation into host DNA and virus production, (3) simultaneous attack on helper T-lymphocytes, (4) progressive decline in T_H cells leading to immunodeficiency. The key points for a 5-mark answer include: identification of HIV as a retrovirus, role of reverse transcriptase, formation of viral DNA, attack on helper T-lymphocytes, and the resulting immunodeficiency that makes the person susceptible to opportunistic infections.
Solution Steps
Step 1: Identify HIV as a retrovirus with RNA genome
Step 2: Explain entry into macrophages and conversion of RNA to viral DNA via reverse transcriptase
Step 3: Describe incorporation of viral DNA into host genome and virus production
Step 4: Explain attack on helper T-lymphocytes and progeny virus release
Step 5: Describe the progressive decrease in T_H cells leading to immunodeficiency and susceptibility to opportunistic infections