The specific labeling in hypertonic medium of a spleen protein.

The biosynthesis of 12 000 dalton protein species released into the medium by mouse spleen was resistant to the inhibitory effect of hypertonic medium on protein synthesis. This protein fraction comprised 10% or more of the total radioactive protein in the medium but could hardly be detected in the spleens. It was labeled very often to a higher extent in diseased animals. It is not related antigenically to either beta-microglobin, mouse-interferon, or to mouse immuno-globulins. A preferential uptake into cells of certain organs, which, when themselves incubated in organ cultures did not synthesize and release the protein, was observed.