Time Course of HIV Infection

This classic graph shows how different markers change across the 3 stages of HIV infection, plotted against time (months early on, then years later).

The 4 Curves Explained

Curve	What it represents
Virus / Viral RNA / p24 antigen	Actual amount of virus in the blood
CD4 lymphocytes	The immune cells HIV destroys
Anti-p24 antibodies	Antibodies against HIV's core protein
Anti-gp120 antibodies	Antibodies against HIV's surface protein

Stage 1: ACUTE (0 - ~3 months)

The virus enters the body and replicates explosively - viral load spikes within the first 1-2 months.
CD4 cells take a sharp hit - they drop suddenly as the virus destroys them.
The immune system fights back: anti-p24 and anti-gp120 antibodies begin rising around week 3-4. This is called seroconversion.
The patient feels acutely ill: fever, sore throat, swollen lymph nodes, rash (like mono). These are the "acute symptoms" shown by the dark triangle on the left.

Key diagnostic point: In the first few weeks (the "window period"), antibody tests can be falsely negative because antibodies haven't formed yet. You need to test for viral RNA or p24 antigen for early diagnosis.

Stage 2: LATENT (months to 3-10+ years)

Viral load settles at a low, stable level called the "viral set point."
CD4 cells partially recover but then begin a slow, gradual decline over years.
Antibody levels (anti-p24 and anti-gp120) remain high and stable - the immune system is actively fighting but slowly losing.
The patient appears clinically well (no symptoms).

Critical concept from the text: This is clinical latency, but NOT microbiological latency. Virus is still replicating constantly inside lymph nodes - the battle is silent but ongoing. The patient is still infectious.

Stage 3: IMMUNODEFICIENCY / AIDS (after 3-10+ years)

CD4 count falls below 400/µL (and eventually below 200/µL, which is the WHO/CDC definition of AIDS).
With the immune system collapsing, viral load surges again - the virus escapes immune control.
Anti-p24 antibodies drop sharply - massive free p24 antigen floods the blood and mops up the antibodies.
Anti-gp120 antibodies fall more gradually as antibody production fails overall.
The patient now gets opportunistic infections (PCP pneumonia, toxoplasmosis, CMV, etc.) and malignancies (Kaposi's sarcoma, lymphomas) - shown by the dark triangle on the right.

Summary Table

Feature	Acute	Latent	AIDS
Viral load	Very HIGH (spike)	Low (set point)	Very HIGH again
CD4 count	Drops sharply	Slow decline	Crashes (<200/µL)
Antibodies	Rising (seroconversion)	High & stable	Falling
Symptoms	Flu-like illness	None (asymptomatic)	Opportunistic infections
Duration	Weeks	Years (avg. ~10 yr)	Months-years

The overall message of this graph: HIV is a slow, progressive war between the virus and the immune system. The immune system holds the virus in check for years, but eventually loses - and when it does, the consequences (AIDS) are severe.

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