Abstract
Macrophages contain high amounts of lysosomal cysteine proteinases that are considered to be important in catabolic process of endogenous and exogenous proteins.
Addition of horseradish peroxidase to the cultured macrophages induced an increase in the density of lysosomes in parallel with the accumulation of peroxidase taken up the heavy lysosomes. Degradation of uptaken peroxidase was inhibited by addition of anticathepsin L antibody to the medium, but not by addition of anti-cathepsin B or H antibody. Treatment of cells with E-64 caused intracellular accumulation of endogenous proteins due to inhibition of lysosomal proteolysis, but pepstatin, a potent inhibitor of cathepsin D, showed much less effect.
Those results suggest a large contribution of cysteine proteinases, especially cathepsin L to the initiation of lysosomal degradation of both endogenous and exogenous proteins. The levels of mRNAs for cathepsin L and H and cystatin β in macrophages obtained from rats injected with sodium caseinate were several times as high as those in resident macrophages.
