Derived from the bone marrow and spleen, these cells are transformed into plasma cells, during infections, and produce large quantities of antibody directed at specific pathogens. In persons living with AIDS, the functional ability of both the B and the T lymphocytes is damaged, with the T lymphocytes being the principal site of infection by HIV.

A measurement of some property, such as HIV viral load or CD4 cell count, that is taken before some change in therapy - such as beginning anti-HIV medications or changing to a different drug combination.

The components of DNA which pair to make the �rungs� of the DNA ladder. There are four types of bases in DNA which bond in complementary pairs: Adenine to Thymine and Cytosine to Guanine. In RNA, the base Uracil replaces Thymine.

Any fluid in the human body, such as blood, urine, saliva (spit), sputum, tears, semen, mother's milk, or vaginal secretions. Only blood, semen, mother's milk, and vaginal secretions have been linked directly to the transmission of HIV.

A side effect of many anticancer and antiviral drugs, including AZT. Leads to a decrease in white blood cells, red blood cells, and platelets. Such reductions, in turn, result in anaemia, bacterial infections, and spontaneous or excess bleeding.