DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY
Human red blood cells, activated platelets, T lymphocyte (yellow) and granulocytes (green), coloured scanning electron micrograph (SEM). Human lymphocytes are involved in the specific immune response and are composed mainly of precursor T cells and B cells (pre-T cells and pre-B cells). Pre-T cells circulate in the blood before migrating to the thymus where they develop into specialized cells (helper T cells and killer T cells) that are able to identify antigens and infected tissue. Granulocytes (neutrophils) are leukocytes with granules in their cytoplasm that contain destructive chemicals. Neutrophils are involved in inflammation and other immune responses. They assist in cellular defence (phagocytosis) of pathogenic microorganisms. A neutrophil destroys an antigen by engulfing it and injecting lethal chemicals. Macrophages will arrive later to consume any remaining debris. Magnification: x1,000 when shortest axis printed at 25 millimetres.
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