T-4 cell: T-cells (also called T-Helper Cells) that alert the immune system to produce cytotoxic T lymphocytes against a specific infection.

T-cells (thymus cells): A type of immune system cell which is damaged in the course of HIV infection. CD4 cells are a sub-type of T-cell.

T-helper cell: See T-4 cell and CD4 T cell.

TB: See Tuberculosis.

Transfusion: The process of giving blood or parts of blood, such as serum, plasma, or red blood cells, from one person to another.

Tuberculosis (TB): TB is caused by a bacterium called mycobacterium tuberculosis, which usually leads to an infection of the lungs. Transmission is airborne, and usually occurs in confined areas with poor ventilation. TB is a frequent complication of HIV infection. TB infections in persons with HIV can spread readily and progress rapidly to active disease.