For years, scientists regarded natural killer cells as a blunt instrument of the body's immune defense system. Born to kill, these cells were thought to travel straight from the bone marrow, where they are manufactured, to the blood, circulating there and infiltrating the sites of early tumors or infectious agents in the body.
Now, Rockefeller University scientists, led by Christian Mnz, Ph.D., have learned otherwise. Natural killer cells, Mnz and his colleagues say, have to be nurtured. Their ability to destroy tumor and infected cells is not present at birth.
This new insight paves the road to changes in bone marrow and stem cell transplant procedures and will enable scientists to pursue research into activating natural killer cells to help the body fight emerging infections and tumors.
In two separate papers in the February issue of The Journal of Immunology, Mnz, postdoctoral associate Guido Ferlazzo, Ph.D. and their colleagues, show that natural killer cells accumulate mostly in "secondary lymphoid tissues" -- the tonsils, lymph nodes and spleen -- after emerging from the bone marrow. There, the natural killer cells await activation (probably after stimulation by sentinel dendritic cells) before they react in two distinct modes. In one mode, they promptly secrete cytokines, chemical messenger proteins, which modulate emerging T and B immune cell responses. In the other, they become potent killers of tumors and virus-infected cells. While natural killer cells do provide a crucial first defense against many infectious agents and tumor cells, they do so with more discrimination than raw determination.
"Natural killer cells burst forth from the the tonsils, lymph nodes and spleen, and destroy infected and cancerous cells while the immune system's T and B cells are still mobilizing," says Mnz. "Without natural killer cells, threatening conditions can get a strong
Contact: Lynn Love