One of the two major classes of lymphocytes, B lymphocytes are blood cells of the immune system, derived from the bone marrow and spleen; they are involved in the production of antibodies. During infections, these cells are transformed into plasma cells that produce large quantities of antibody directed at specific pathogens. When antibodies bind to foreign proteins, such as those that occur naturally on the surfaces of bacteria, they mark the foreign cells for consumption by other cells of the immune system. This transformation occurs through interactions with various types of T cells and other components of the immune system. 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 microscopic organism composed of a single cell. Many bacteria can cause disease in humans.

1. Information gathered at the beginning of a study from which variations found in the study are measured. 2. A known value or quantity with which an unknown is compared when measured or assessed. 3. The initial time point in a clinical trial, just before a participant starts to receive the experimental treatment which is being tested. At this reference point, measurable values such as CD4 count are recorded. Safety and efficacy of a drug are often determined by monitoring changes from the baseline values.

When a point of view prevents impartial judgment on issues relating to the subject of that point of view. In clinical studies, bias is controlled by blinding and randomization.

A breakdown product of red blood cells, bilirubin is removed from the bloodstream by the liver. High levels of bilirubin cause jaundice (yellowing of the skin) and may indicate hepatitis or other liver problems.

A red pigment occurring in liver bile, blood, and urine. Its measurement can be used as an indication of the health of the liver. Bilirubin is the product of the breakdown of hemoglobin in red blood cells. It is removed from the blood and processed by the liver, which secretes it into the digestive tract. An elevated level of bilirubin in blood serum is an indication of liver disease or drug-induced liver impairment.

The extent to which an oral medication is absorbed in the digestive tract and reaches the bloodstream, thereby permitting access to the site of action.

Surgical removal of a piece of tissue from a living subject for microscopic examination to make a diagnosis (e.g., to determine whether abnormal cells such as cancer cells are present).

A randomized trial is "Blind" if the participant is not told which arm of the trial he is on. A clinical trial is "Blind" if participants are unaware on whether they are in the experimental or control arm of the study; also called masked.

The transient detection of a viral load level after a period of time when viral load was undetectable. It is usually defined as a viral load of 50 to 500 copies/mL after viral load <50 copies/mL on at least two consecutive occasions.

A selective barrier (obstacle) between circulating blood and brain tissues that prevents damaging substances from reaching the brain. Certain compounds readily cross the blood-brain barrier; others are completely blocked.