Which of the following is the primary target cell for HIV infection?

Explanation

## HIV Target Cell Recognition **Key Point:** HIV specifically targets cells expressing the CD4 receptor and either CCR5 or CXCR4 co-receptors on their surface. ### Primary Target: CD4+ T Helper Lymphocytes CD4+ T lymphocytes (helper T cells) are the primary target cells for HIV infection because: 1. **CD4 receptor expression** — CD4 is the main attachment receptor for HIV gp120 envelope protein 2. **Co-receptor availability** — CD4+ cells express CCR5 (R5-tropic, early infection) or CXCR4 (X4-tropic, later infection) co-receptors 3. **Functional consequence** — Infection and destruction of CD4+ cells leads to progressive immunodeficiency ### Secondary Target Cells Other cells with CD4 expression can also be infected: - Macrophages (express CD4 + CCR5) - Dendritic cells (express CD4 + CCR5) - Microglial cells in CNS (express CD4 + CCR5) However, CD4+ T lymphocytes remain the primary and most clinically significant target. **High-Yield:** The CD4 count is the most important marker of immune function in HIV disease; CD4 <200 cells/μL defines AIDS and mandates opportunistic infection prophylaxis. **Clinical Pearl:** Progressive loss of CD4+ T cells is the hallmark of HIV pathogenesis and determines the risk of opportunistic infections (OIs) — CD4 <200 → *Pneumocystis jirovecii* pneumonia (PCP); CD4 <50 → cytomegalovirus (CMV) and *Mycobacterium avium* complex (MAC).