The organ distribution of F protein in the mouse

F protein is of unknown function and found principally in the liver, with smaller amounts detectable by gel diffusion and immunostaining in kidney and brain. By taking advantage of a newly developed radioimmunoassay, capable of detecting down to 1 ng ml-1 of F protein, the organ distribution of this molecule in the mouse was re-examined. F protein was not confined to the previously known tissues and indeed was detected at different levels in every organ studied. The highest concentration (6-10 mg g-1 wet tissue) was found in the liver, but significant amounts (2-25 micrograms g-1) were also found in kidney, heart, and brain. Lower quantities were detectable in all other tissues studied. The presence of F protein in the thymus, and the lack of tolerance to this in bone marrow chimaeras between mice of different F protein types, places certain constraints on the amount and/or location of a protein required for tolerization.