CD14

CD14 is a protein used as a marker of monocytes and involved in recognition of bacterial lipopolysaccharide. These are two different uses of the same molecule: measuring which cells carry a marker and perturbing a molecular contribution to a response.

A 1990 experiment linked CD14 to recognition of lipopolysaccharide associated with lipopolysaccharide-binding protein. Blocking CD14 with monoclonal antibodies prevented the measured synthesis of tumor necrosis factor in the tested whole-blood preparation after lipopolysaccharide stimulation. This connects recognition with a defined functional endpoint; it does not establish that CD14 alone supplies the complete signal transduction pathway.^[ref]

For an original quantitative illustration, suppose baseline-subtracted tumor necrosis factor readout is 100 arbitrary units with a control antibody and 10 with a blocking antibody. The reduction is $(100-10)/100=0.90$, or 90 percent. These invented measurements show how to state the response being reduced. Matching viable-cell counts and background conditions would help distinguish specific blockade from nonspecific loss of responding cells.

Flow cytometry supplies a complementary kind of evidence. A 1989 study used CD14 and CD16 together to distinguish a monocyte subpopulation. A marker-defined population and an antibody-sensitive response describe different properties; neither observation makes every marker-positive cell functionally identical.^[ref]