Budding HIV particles. Coloured scanning electron micrograph (SEM) of human immunodeficiency virus (HIV) particles (yellow) budding from the surface of an T lymphocyte from the H9 cell line. HIV attacks CD4+ T-lymphocytes, white blood cells, a crucial part of the body's immune system. It enters the cell, hijacks the cell's machinery to make more copies of the virus, and the new virus particles then burst from the membrane of the cell, killing it. This severely weakens the immune system, causing AIDS (acquired immunodeficiency syndrome). The disease makes the patient susceptible to diseases that would otherwise be harmless.