A new look at reticuloendothelial blockade.

The characteristics of so-called reticuloendothelial blockade have been reinvestigated in mice using organ uptake, rather than blood clearance, as the main method of assessment. Blockade was induced by using i.v. dextran sulphate. I.v. 51Cr-labelled sheep red blood cells were used as test particles. Although clearance of colloid from the bloodstream induced prolongation of reticuloendothelial clearance of a subsequent dose of test particles, this was solely due to depression of hepatic phagocytosis and the splenic and bone-marrow clearance remained unimpaired. Because of this highly selective action of i.v. blockading colloid, and because testing via the i.v. route can only provide information about macrophages which line blood channels, the expression reticuloendothelial blockade is entirely inappropriate to describe these phenomena. Unexpectedly, the effects could be quantitated using a wide range of doses of this test particle and saturating doses were not required.