CD4+ T cell

A cell of the immune system, also known as a “helper” cell, that helps other immune system cells produce antibodies. CD4+ T cells are the cell type that are infected and destroyed by HIV.


The basic unit of all living things

Cell-mediated immunity

Part of the immune system in which specific immune system cells, such as cytotoxic T cells, directly attack infected cells


One of a segment of DNA that together make up the genetic information of an organism. Humans have 23 pairs of chromosomes.


A group of organisms that includes all descendants of one common ancestor


Group of individuals used in a study that have a statistical factor, such as age, in common


A small protein that is secreted by certain cells of the immune system that plays an important role in cell signalling by affecting the behavior of other cells. Examples include interferon and interleukin. 

Cytotoxic T cell

Also known as “killer” T cells, a type of immune system cell that can directly attack infected cells.