Question

The HIV virus targets which CD receptor on immune cells?

• A. CD8
• B. CD4
• C. CD3
• D. CD20

Hint:

Recall which surface glycoprotein on CD4+ helper T cells is bound by HIV envelope protein gp120 to initiate infection.

Answer 1

The Correct Option is B

HIV-1 is a lentivirus with a single-stranded positive-sense RNA genome. Its surface glycoprotein $\text{gp120}$ identifies and binds $\text{CD4}$ -- the primary receptor expressed on CD4+ T helper lymphocytes, monocytes, macrophages, and dendritic cells.

Entry mechanism:
1. gp120 binds CD4 (high-affinity interaction)
2. Conformational change in gp120 exposes V3 loop
3. V3 loop binds co-receptor (CCR5 or CXCR4)
4. gp41 undergoes conformational change, enabling membrane fusion
5. Viral RNA and enzymes enter the cell

Clinical relevance of CD4 count:
- CD4 < 500: early immunosuppression
- CD4 < 200: AIDS-defining; risk of $\textit{Pneumocystis jirovecii}$ pneumonia
- CD4 < 100: risk of CMV retinitis, MAC infection
- CD4 < 50: risk of CNS lymphoma, CMV encephalitis

Note: Individuals homozygous for CCR5-Delta32 deletion are highly resistant to HIV infection (CCR5 is primary co-receptor for R5 strains).

\[\boxed{\text{CD4}}\]