Читать книгу Immunology - Richard Coico - Страница 71

Another hallmark of innate immunity is the ability of certain innate immune cells to sample their environment by engulfing macroparticles (endocytosis) or individual cells (phagocytosis). Endocytosis is the process whereby macromolecules present in extracellular tissue fluid are ingested by cells. This can occur either by pinocytosis, which involves nonspecific membrane invagination, or by receptor‐mediated endocytosis, a process involving the selective binding of macromolecules to specific membrane receptors. In both cases, ingestion of the foreign macromolecules generates endocytic vesicles filled with the foreign material, which then fuse with acidic compartments called endosomes. Endosomes then fuse with lysosomes containing degradative enzymes (e.g., nucleases, lipases, proteases) to reduce the ingested macromolecules to small breakdown products, including nucleotides, sugars, and peptides (Figure 3.8).