In a process still imperfectly understood, HIV infects the CD4 cells (also called T4 or T-helper cells) of the body's immune system, cells that are necessary to activate B-lymphocytes and induce the production of antibodies (see immunity). Although the body fights back, producing billions of lymphocytes daily to fight the billions of copies of the virus, the immune system is eventually overwhelmed, and the body is left vulnerable to opportunistic infections and cancers.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.