Helper T-cells (also T-helper cells, CD4 cells)		T-lymphocytes bearing the CD4+ cell surface marker. Helper T-cells are the chief regulatory cells of the immune system, controlling activities such as turning antibody-producing B-cells and cytolytic (CD8) T-cells on and off. They are the main targets of HIV infection.
HIV (human immunodeficiency virus)		A pathogenic retrovirus that causes AIDS (acquired immune deficiency syndrome). It replicates in helper T-cells and results in their destruction.