How does HIV infection lead to a decrease in the number of helper T-l…

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

HIV, the virus that causes AIDS, enters helper T-lymphocytes (T_H), multiplies inside them and releases new viruses into the blood. These viruses attack more helper T-cells, so their number falls steadily. Helper T-cells direct the immune response, so the person can no longer fight even common infections.

Option (1) The virus directly kills helper T-lymphocytes — Correct. The virus itself destroys the helper T-cells it infects, and its progeny attack more of them.

Option (2) The virus inhibits the production of helper T-lymphocytes — Incorrect. The production of these cells is not blocked. The fall is due to the virus attacking cells that already exist.

Option (3) The virus triggers an immune response that destroys helper T-lymphocytes — Incorrect. The cells are destroyed by the virus, not by the body’s own immune response.

Option (4) The virus causes helper T-lymphocytes to migrate out of the body — Incorrect. Helper T-cells do not leave the body. The virus destroys them inside it.

NCERT Extract:
AIDS – “… 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.”