- The human immunodeficiency virus (HIV) primarily infects CD4+ T-cells because these cells express the CD4 receptor, which HIV uses as the main entry point.
- The virus also requires co-receptors (CCR5 or CXCR4) found on CD4+ T-cells to gain entry. Infection leads to the progressive depletion of these cells, causing immune system failure.
- CD8+ T-cells, B lymphocytes, and monocytes do not express CD4 receptors in sufficient amounts, so they are not the primary targets.
- This selective infection is crucial for the pathogenesis of HIV/AIDS.

Reference: Harrison's Principles of Internal Medicine, 20th Edition, Chapter 243