Which liver macrophages are part of the reticuloendothelial system?

• A. Kupffer cells (RES)
• B. Hepatocytes
• C. Stellate cells
• D. Endothelial cells

Answer: (A)

Kupffer cells are the liver macrophages that form part of the reticuloendothelial system. They line the hepatic sinusoids and act as resident phagocytes, screening portal blood for bacteria and debris, clearing senescent red blood cells, and recycling iron. This macrophage-focused function is what aligns them with the reticuloendothelial (mononuclear phagocyte) system. The other liver cell types listed aren’t macrophages: hepatocytes carry out metabolism and secretory functions, stellate (Ito) cells store vitamin A and can produce extracellular matrix, and endothelial cells line the sinusoids and vessels without performing macrophage phagocytosis.