Liposomes in Host Defense Mechanism: A Key Role for Macrophages

Abstract

Liposomes can be used as carriers for antigens, immunomodulators and cytotoxic drugs. Such liposomes may serve as a tool to manipulate immune and non-immune host defense mechanisms. In most cases their effects are mediated by macrophages. Macrophages seem to be involved in humoral (antibody) responses and in cytotoxic T-lymphocyte responses. They are also important in non-immune defense mechanisms against foreign invaders and altered self. Which macrophages can be influenced by the liposome encapsulated molecules depends on the administration route of the liposomes. The macrophages ingest the liposomes. Once within the cell, lysosomal phospholipases disrupt the phospholipid bilayers. In this way, encapsulated molecules are released in the cell. Such liposome delivered molecules can be processed (antigens), activate the macrophage (immunomodulators) or disturb the metabolism of the cells (cytotoxic drugs). That the latter inhibition of macrophage functions may result in immunopotentiation is explained by the fact that certain macrophages are regulating immune functions by suppression.