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india Updated: Dec 13, 2003 12:55 IST

Protection from a disease as a result of previous exposure to the disease-causing infectious agent or antigen. The protection can be a result of having had the disease or having received a vaccine to prevent getting the disease.

Occurring before birth.

A Y-shaped protein on the surface of B cells that is secreted into the blood or lymph in response to an antigenic stimulus to neutralise infections or malignant cells.

Any substance that stimulates the immune system to produce antibodies (proteins that fight antigens). Antigens are often foreign substances such as bacteria or viruses that invade the body.

Substances used to kill or inhibit the multiplication of retroviruses such as HIV.

A substance or process that destroys a virus or suppresses its replication (i.e., reproduction).

A person who does not show the symptoms associated with HIV.

Also called B cells, they are one of the two major classes of lymphocytes, these are immune system cells, derived from the bone marrow and spleen. These cells are involved in the production of antibodies.

Also called Computed Tomography Scan or CAT Scan, this is a form of radiography where an x-ray in which a three-dimensional image of a body structure is constructed by computer from a series of cross-sectional images made along an axis.

Cell surface molecule, which is needed along with the primary receptor, the CD4 molecule, in order to fuse with the membranes of the immune system cells. Researchers have found that the strains of HIV most often transmitted from person to person require the CCR5 molecule and CD4 molecule in order for HIV to enter the cell. In addition to its role in fusion, CKR5 is a receptor for certain immune-signaling molecules called chemokines that are known to suppress HIV infection of cells.

CD4 (T4) or CD4 + CELLS
Also known as T helper cells, these are a type of T cell involved in protecting against viral and fungal infections. Also HIV's favourite targets are cells that have a docking molecule called 'cluster designation 4' (CD4) on their surfaces. Cells with this molecule are known as CD4-positive (or CD4+) cells.

A highly contagious sexually transmitted disease caused by the Haemophilus ducreyi bacterium with symptoms appearing 3 to 5 days after exposure. It appears as a tender papule that becomes pustular and then ulcerative.

A sexually transmitted disease (STD) caused by Chlamydia trachomatis that infects the genital tract. The infection is frequently asymptomatic (i.e., shows no symptoms), but if left untreated, it can cause sterility in women.

The study of the incidence and distribution of diseases and of their control and prevention

An infection caused by Neisseria gonorrhoeae. Although gonorrhea is considered primarily a sexually transmitted disease it can also be transmitted to newborns during the birth process.

A type of white blood cell. Also referred to as the T blood cell

Red Ribbon is the international symbol of HIV and AIDS awareness.

A rudimentary form of virus which carries its genetic information in the form of RNA. This means that it can easily be copied into the DNA of the host cell's chromosomes. HIV is a retrovirus - some other members of the retrovirus family cause cancers.

Male, Female or transgender adults and young people who receive money or goods in exchange for sexual services, either regularly or occasionally, and who may or may not consciously define those activities as income generating

The process by which the virus is passed from one person to another. Among the body fluids that are the most frequent carriers are blood, semen, vaginal secretions and breast milk
The most common forms of transmission are through unprotected sexual intercourse, by sharing needles when injecting drugs and from mother to child when breastfeeding.

The amount of HIV in the human blood. This is measured in the number of copies of the virus per millilitre of blood plasma.

The time taken for HIV to produce antibodies. This ranges from two to 24 weeks. During this period a person may be infected and capable of infecting others but tests may show a negative result.

First Published: Dec 01, 2003 13:39 IST