(T Cells) A white blood cell that recognises foreign proteins (e.g. bacteria, transplanted tissue) and mobilises other cells to destroy the invading organism or foreign tissue. HIV infects certain T lymphocytes (CD4 lymphocytes), thereby causing immunodeficiency.

Thermostable DNA Polymerase originally isolated from the bacterium Thermus aquaticus. Taq has optimal activity at 70�80� C and is not degraded during the high heat denaturation steps of PCR.

A nucleotide sequence of DNA or RNA within the organism genome that is known, conserved and characteristic for the intended test.

An RNA or DNA strand that provides the pattern for synthesis of a complementary strand. In most organisms DNA is the template for RNA; in HIV and other retroviruses RNA is the template for DNA.

Also called treatment vaccine. A vaccine designed to boost the immune response to HIV in persons already infected with the virus. A therapeutic vaccine is different from a preventive vaccine, which is designed to prevent a disease from becoming established in a person.

Sore patches in the mouth caused by the fungus Candida albicans. Thrush is one of the most frequent early symptoms or signs of an immune disorder. The fungus commonly lives in the mouth, but only causes problems when the body's resistance is reduced either by antibiotics that have reduced the number of competitive organisms in the mouth, or by an immune deficiency, such as HIV disease. See Candidiasis.

(TOXOPLASMIC ENCEPHALITIS) Toxoplasmosis is an infection that is caused by the protozoan (see protozoa) parasite, Toxoplasma gondii. The parasite is carried by cats, birds, and other animals, and is found in soil contaminated by cat faeces and in meat, particularly pork. The parasite can infect the lungs, retina of the eye, heart, pancreas, liver, colon, and testes. In HIV-infected persons, the most common site of toxoplasmosis is the brain. When T. gondii invades the brain, causing inflammation, the condition is called toxoplasmic encephalitis. While the disease in HIV-infected persons can generally be treated with some success, lifelong therapy is required to prevent its reoccurrence.

The process of making RNA from DNA.

HIV is spread most commonly by sexual contact with an infected partner. The virus can enter the body through the mucosal lining of the vagina, vulva, penis, rectum, or, rarely, the mouth during sex. The likelihood of transmission is increased by factors that may damage these linings, especially other sexually transmitted diseases that cause ulcers or inflammation. HIV also is spread through contact with infected blood, most often by the sharing of drug needles or syringes contaminated with minute quantities of blood containing the virus. Children can contract HIV from their infected mothers during either pregnancy or birth, or postnatally, through breast-feeding. In developed countries, HIV is now only rarely transmitted by transfusion of blood or blood products because of screening measures.

A bacterial infection caused by Mycobacterium tuberculosis. TB bacteria are spread by airborne droplets expelled from the lungs when a person with active TB coughs, sneezes, or speaks. Exposure to these droplets can lead to infection in the air sacs of the lungs. The immune defences of healthy people usually prevent TB infection from spreading beyond a very small area of the lungs. TB is seen with increasing frequency among persons infected with HIV. Most cases of TB occur in the lungs (pulmonary TB). However, the disease may also occur in the larynx, lymph nodes, brain, kidneys, or bones (extrapulmonary TB). Extrapulmonary TB infections are more common among persons living with HIV. See Multidrug Resistant TB.