How HIV Replicates: Reverse Transcriptase and the Attack on Helper T-Cells
Biology · Human Health and Diseases · NEET
After HIV enters the body, it first infects macrophages. Inside, its enzyme reverse transcriptase copies the viral RNA into viral DNA, which joins the host cell's DNA and turns the cell into a "HIV factory." HIV then enters helper T-lymphocytes (TH cells), replicates, and slowly destroys them, which weakens immunity. Memory hook: "RNA needs Reverse transcriptase to become DNA — macrophage FIRST, TH cells DIE."
HIV enters macrophages first, uses reverse transcriptase to make viral DNA, then infects and destroys helper T-cells (TH) - the drop in TH cells causes AIDS.
Your doubts, answered
Which cell does HIV infect FIRST after entering the body?
HIV first enters macrophages. Inside the macrophage, the RNA genome is copied into viral DNA by reverse transcriptase. This viral DNA joins the host DNA and makes the macrophage keep producing virus, so NCERT calls the macrophage an 'HIV factory'. This is a common NEET point: macrophage is first, not the T-cell.
So does HIV replicate in macrophages or in helper T-cells?
Both. HIV replicates in macrophages AND in helper T-lymphocytes (TH cells). But the exact NEET answer to 'in which blood corpuscle does HIV replicate and produce progeny viruses' is TH cells (helper T-lymphocytes), because the progeny released into the blood attack other helper T-cells. This was asked in NEET 2023.
What exactly does reverse transcriptase do?
Reverse transcriptase is an enzyme carried by HIV. It does the reverse of normal transcription: it makes DNA from RNA (RNA to DNA). This viral DNA then gets incorporated into the host cell's DNA. Normal cells make RNA from DNA, so this reverse step is why the virus is special.
Why is HIV called a retrovirus?
HIV is called a retrovirus because it carries an RNA genome plus reverse transcriptase, letting it make DNA from its RNA ('retro' = backward). NCERT says HIV is a retrovirus with an envelope enclosing the RNA genome. It carries two identical single-stranded RNA molecules and two reverse transcriptase enzymes.
Why does HIV cause immunodeficiency (AIDS)?
Each round of replication in helper T-cells releases progeny viruses that attack more helper T-cells. This causes a progressive decrease in the number of helper T-lymphocytes. Because helper T-cells run the immune response, the person can no longer fight infections that a healthy body would easily overcome (bacteria like Mycobacterium, viruses, fungi, and parasites like Toxoplasma).
Which cells does HIV destroy over time?
HIV progressively destroys helper T-lymphocytes (TH cells). The macrophage keeps making virus but the fall in helper T-cell number is what causes the immunodeficiency. Fewer helper T-cells means the whole acquired immune response collapses.
⚠️ The NEET trap ✗ HIV replicates mainly in B-lymphocytes (or basophils/eosinophils) and destroys them. ✓ HIV replicates in macrophages first, then in helper T-lymphocytes (TH cells), and it is the helper T-cells whose numbers progressively fall. 🧠 NEET 2023 asked exactly this: the answer is TH cells, NOT B-lymphocytes. Memory line: 'HIV loves the HELPER (T), not the B.'
Real NEET questions
NEET 2023 Phase 1
In which blood corpuscles, the HIV undergoes replication and produces progeny viruses?
A · TH cells ✓
B · B-lymphocytes
C · Basophils
D · Eosinophils
Solution: After HIV enters the body it first infects macrophages, but it also enters helper T-lymphocytes (TH), where it replicates and produces progeny viruses that go on to attack other helper T-cells. This progressive loss of TH cells causes the immunodeficiency. B-lymphocytes, basophils and eosinophils are not the cells NCERT names for HIV replication. NCERT: 'HIV enters into helper T-lymphocytes (TH), replicates and produce progeny viruses.'
NEET 2016 Phase 2
Which of the following is correct regarding AIDS causative agent HIV?
A · HIV is enveloped virus containing one molecule of single-stranded RNA and one molecule of reverse transcriptase
B · HIV is enveloped virus that contains two identical molecules of single-stranded RNA and two molecules of reverse transcriptase ✓
C · HIV is non-enveloped retrovirus
D · HIV does not escape but attacks the acquired immune response
Solution: HIV is a retrovirus with an envelope enclosing its RNA genome. The particle carries two identical single-stranded RNA molecules and two copies of reverse transcriptase, which converts viral RNA into DNA inside the host cell. Option A understates the genome; C is wrong because HIV IS enveloped; D is false because HIV does escape immune detection and destroys helper T-cells. NCERT: 'AIDS is caused by HIV, a member of a group of viruses called retrovirus, which have an envelope enclosing the RNA genome.'
Solved Human Health and Diseases NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
What is the correct order of HIV replication in the body?
1) HIV enters the body. 2) It enters macrophages, where reverse transcriptase copies its RNA into viral DNA. 3) This viral DNA joins the host cell DNA and directs virus production (macrophage = HIV factory). 4) HIV enters helper T-lymphocytes (TH cells) and replicates. 5) Progeny viruses attack more helper T-cells, so their number falls progressively, causing AIDS.
Is reverse transcriptase made by the host cell or carried by HIV?
It is carried by HIV itself. The virus brings its own reverse transcriptase enzyme so it can make viral DNA from its RNA as soon as it enters a host cell. NCERT notes HIV carries two molecules of reverse transcriptase.
What happens to helper T-cell numbers in AIDS?
They fall progressively. Each cycle of replication in helper T-cells releases progeny that attack more helper T-cells. As helper T-cell numbers drop, the person cannot fight infections (Mycobacterium, viruses, fungi, Toxoplasma) and becomes immunodeficient.
What test is used to diagnose AIDS?
The widely used diagnostic test is ELISA (enzyme linked immuno-sorbent assay). Treatment uses anti-retroviral drugs, which only prolong the patient's life but cannot cure the disease.
How long is the gap between HIV infection and AIDS symptoms?
NCERT states there is a time-lag, often a few months to many years (usually 5 to 10 years), between HIV infection and the appearance of AIDS symptoms.
