How does HIV infection lead to a decrease in the number of helper T-lymphocytes?

The virus directly kills helper T-lymphocytes

The correct answer is Option (1) - The virus directly kills helper T-lymphocytes.

HIV infection leads to a decrease in the number of helper T-lymphocytes (also known as CD4+ T-cells) primarily because the virus directly kills these cells. HIV specifically targets and infects helper T-lymphocytes, which are a crucial part of the immune system involved in coordinating immune responses.

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.

The progressive decrease in the number of helper T-lymphocytes weakens the immune system and impairs its ability to mount an effective immune response against various infections and diseases. This immune deficiency is a hallmark of HIV/AIDS and makes individuals more susceptible to opportunistic infections and other complications associated with the disease.