Describe the effects of HIV on the immune system and explain why a person infected with HIV becomes increasingly vulnerable to other infections over time.

HIV infects and destroys CD4+ T‑lymphocytes, the main helper cells of the immune system.

The loss of CD4+ cells reduces the ability of B‑cells to recognise antigens and produce specific antibodies.

With fewer helper cells, the overall immune response is weakened and eventually becomes non‑functional, resulting in AIDS.

A weakened immune system can no longer recognise and eliminate many pathogens that a healthy body would normally clear, so the person becomes increasingly vulnerable to opportunistic infections.