Scanning Electron Micrograph (SEM) showing Human Immunodeficiency Virus (HIV) particles, the cause of AIDS (Acquired Immune Deficiency Syndrome). HIV infects T4 lymphocytes, and uses the lymphocytes' own cellular machinery to make more copies of itself (HIV). These copies then burst out of the cell, killing it and infecting other cells. T4 lymphocytes are white blood cells, and an important part of the immune system. AIDS severely damages the immune system, making normally harmless infections potentially fatal. Magnification: 130,000X at 5 x 7" print size.