In other words, they had a hunch traditional thinking about the origin of human NK cells might be wrong.
In building a case to support their beliefs, they first identified the NK precursor cell, then, they measured the number of the precursors in different parts of the body. Through flow cytometry, they discovered that while NK precursors make up about 1 percent of bone marrow progenitor cells and 6 percent of circulating blood progenitor cells, they comprise virtually all of the progenitor cells found in lymph nodes.
Interestingly, Gerard Nuovo, a pathologist and co-author of the study, discovered that these novel NK precursor cells are not randomly strewn throughout the lymph nodes, but rather localized near special sites called parafollicular regions, rich in T cells and NK bright cells.
"We thought this was pretty interesting because we know that in order for these NK precursor cells to grow and differentiate, they need one of two cytokines, interleukin-2 or interleukin-15," says Freud. "So it may not be coincidental that two types of immune cells that make those substances T cells and dendritic cells just happen to reside in lymph nodes, too."
Freud also makes the provocative observation that lymph nodes, while full of CD56 bright cells, are significantly lacking in their counterparts, the CD56 dim cells.
"Our next goal is to determine if there is some developmental continuum at work here, supporting the notion that CD56 bright cells are really just immature CD56 cells," he adds.
"This study raises almost as many questions as it answers," says Caligiuri, "Finding these nursery sites of NK cells is just the first step. We feel this is the first solid evidence supporting a new model of NK cell development, but we also know that more work needs to be done to fill in so
Contact: Michelle Gailiun
Ohio State University