KEITH R. PORTER / SCIENCE PHOTO LIBRARY KEITH R. PORTER / SCIENCE PHOTO LIBRARY
Scanning electron micrograph (SEM) of lymphocytic leukemia or chronic lymphocytic leukemia (CLL). CLL is a type of leukemia that affects the B cells, which are created in the bone marrow, and fight infection. The disease damages the B cells' DNA, rendering them incapable of fighting infection. These damaged B cells reproduce uncontrollably, crowding out otherwise healthy lymphocytes, thus compromising the body's ability to fight infection even further. The disease occurs only in adults who are over the age of 50.
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