A Close Look at Lymphocytes

At first glance, they seem to be some kind of exotic aquatic life photographed against a background of seaweed. But the spherical creatures portrayed in the pictures taken by scientists from Manhattan's Memorial Sloan-Kettering Cancer Center and Rockefeller University swim not in the sea but in the human bloodstream. They are lymphocytes, cells that are essential parts of the immune system and protect the body against invasion by germs and other foreign matter. Magnified about 13,000 times by a scanning electron microscope, they reveal for the first time structural differences between the two kinds of lymphocytes.

The B-cells (top), which have about 150 finger-Like protrusions on their surfaces, produce the antibodies that lock onto invading cells and other foreign bodies, making them more susceptible to scavenger cells. Tcells, which have only a handful of protrusions on their otherwise smooth surfaces, proliferate, flock to the site of an infection and attack the invaders directly, destroying them chemically.

Eventually, the physical differences between the two types of lymphocytes may help scientists determine how each performs its specific duties. For now, however, recognition of the physical difference gives doctors a potential new tool in diagnosing disease. In blood samples from healthy people, about 20% of the lymphocytes are B-cells, the remainder Tcells. The percentage changes in some ill people; in most chronic lymphocytic leukemia patients, for example, the majority of the cells are B-cells, a condition that can be now determined with speed and precision.

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