SINCLAIR STAMMERS / SCIENCE PHOTO LIBRARY SINCLAIR STAMMERS / SCIENCE PHOTO LIBRARY
HIV+ blood test by HLA typing. Fluorescent light micrograph view of human white blood cells testing HIV-positive, in a "Human Leucocyte Antigen" (HLA) blood-typing test. HIV (Human Immunodeficiency Virus) is the virus which causes AIDS. Here, a patient's "leucocyte" white blood cells are coated on small orange glass beads. An HIV-positive result is obtained when cells on the beads do not fluoresce green, but instead die. The cells die when an antibody-antigen complex is active because the patient's blood sample contains antigens from the HIV virus. The HLA test (called a complement- fixation test) can tell the severity of infection by the strength of the antibody-antigen reaction.
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