8536dch010079/5/0211:47 AM Page7mac46mac46:385reb: Overview of the Immune System cHAP ph of macrophage(pink) attack gocytized as scribed in part b and breakdown products secreted. The monocyte sle)has been recruited to the vicinity of the encounter by solubl factors secreted by the macrophage. The red sphere is an erythrocyte Schematic diagram of the steps in phagocytosis of a bacterium purified LPS leads to an acute inflammatory response(see be- low). The mechanism for this response is via a TLR on macrophages that recognizes LPS and elicits a variety of mole cules in the inflammatory response upon exposure. When the TLR is exposed to the LpS upon local invasion by a Gram-neg ative bacterium, the contained response results in elimination of the bacterial challenge Cells That Ingest and Destroy Pathogens Make Up a Phagocytic Barrier to Infection Another important innate defense mechanism is the inges- to membrane evaginations tion of extracellular particulate material by phagocytosis. called pseudopodia Phagocytosis is one type of ende the general term for the uptake by a cell of material from its environment. In 31 phagocytosis, a cell,'s plasma membrane expands around the forming phag 20 ate material, which may include whole pathogen microorganisms, to form large vesicles called phagosor (Figure 1-3). Most phagocytosis is conducted by specialized Phagosome fuses with cells, such as blood monocytes, neutrophils, and tissue macrophages(see Chapter 2). Most cell types are capable of 0(83 other forms of endocytosis, such as receptor-mediated endo- ysosomal enzymes digest cytosis, in which extracellular molecules are internalized after captured material binding by specific cellular receptors, and pinocytosis, the process by which cells take up fluid from the surrounding medium along with any molecules contained in it. Digestion products are released from cell Inflammation Represents a Complex Sequence of Events That Stimulates Immune Responses Tissue damage caused by a wound or by an invading genic microorganism induces a complex sequence of events or inflammation"as rubor(redness), tumor(swelling) collectively known as the inflammatory response. As de- calor(heat), and dolor(pain). In the second century AD,an- scribed above, a molecular component of a microbe, such other physician, Galen, added a fifth sign: functio laesa(loss of function). The cardinal signs of inflammation reflect the LPS,may trigger an inflammatory response via interaction three major events of an inflammatory response( Figure 1-4) with cell surface receptors. The end result of inflammation may be the marshalling of a specific immune response to the 1. VasodilationH-an increase in the diameter of blood invasion or clearance of the invader by components of the vessels--of nearby capillaries occurs as the vessels that innate immune system. Many of the classic features of the arry blood away from the affected area constrict, inflammatory response were described as early as 1600 BC, in resulting in engorgement of the capillary network. The Roman physician Celsus described the"four cardinal signs (erythema)and an increase in tissue temperature Egyptian papyrus writings. In the first century AD, the engorged capillaries are responsible for tissue rednesystemic exposure of mammals to relatively small quantities of purified LPS leads to an acute inflammatory response (see be￾low). The mechanism for this response is via a TLR on macrophages that recognizes LPS and elicits a variety of mole￾cules in the inflammatory response upon exposure. When the TLR is exposed to the LPS upon local invasion by a Gram-neg￾ative bacterium, the contained response results in elimination of the bacterial challenge. Cells That Ingest and Destroy Pathogens Make Up a Phagocytic Barrier to Infection Another important innate defense mechanism is the inges￾tion of extracellular particulate material by phagocytosis. Phagocytosis is one type of endocytosis, the general term for the uptake by a cell of material from its environment. In phagocytosis, a cell’s plasma membrane expands around the particulate material, which may include whole pathogenic microorganisms, to form large vesicles called phagosomes (Figure 1-3). Most phagocytosis is conducted by specialized cells, such as blood monocytes, neutrophils, and tissue macrophages (see Chapter 2). Most cell types are capable of other forms of endocytosis, such as receptor-mediated endo￾cytosis, in which extracellular molecules are internalized after binding by specific cellular receptors, and pinocytosis, the process by which cells take up fluid from the surrounding medium along with any molecules contained in it. Inflammation Represents a Complex Sequence of Events That Stimulates Immune Responses Tissue damage caused by a wound or by an invading patho￾genic microorganism induces a complex sequence of events collectively known as the inflammatory response. As de￾scribed above, a molecular component of a microbe, such as LPS, may trigger an inflammatory response via interaction with cell surface receptors. The end result of inflammation may be the marshalling of a specific immune response to the invasion or clearance of the invader by components of the innate immune system. Many of the classic features of the inflammatory response were described as early as 1600 BC, in Egyptian papyrus writings. In the first century AD, the Roman physician Celsus described the “four cardinal signs Overview of the Immune System CHAPTER 1 7 FIGURE 1-3 (a) Electronmicrograph of macrophage (pink) attack￾ing Escherichia coli (green). The bacteria are phagocytized as de￾scribed in part b and breakdown products secreted. The monocyte (purple) has been recruited to the vicinity of the encounter by soluble factors secreted by the macrophage. The red sphere is an erythrocyte. (b) Schematic diagram of the steps in phagocytosis of a bacterium. [Part a, Dennis Kunkel Microscopy, Inc./Dennis Kunkel.] Bacterium becomes attached to membrane evaginations called pseudopodia Bacterium is ingested, forming phagosome Phagosome fuses with lysosome Lysosomal enzymes digest captured material Digestion products are released from cell 3 2 4 5 1 (a) (b) of inflammation” as rubor (redness), tumor (swelling), calor (heat), and dolor (pain). In the second century AD, an￾other physician, Galen, added a fifth sign: functio laesa (loss of function). The cardinal signs of inflammation reflect the three major events of an inflammatory response (Figure 1-4): 1. Vasodilation—an increase in the diameter of blood vessels—of nearby capillaries occurs as the vessels that carry blood away from the affected area constrict, resulting in engorgement of the capillary network. The engorged capillaries are responsible for tissue redness (erythema) and an increase in tissue temperature. 8536d_ch01_007 9/5/02 11:47 AM Page 7 mac46 mac46:385_reb: