Page 570 - Veterinary Immunology, 10th Edition

phagosomal proteases, and promote antigen loading onto MHC
VetBooks.ir molecules, so enhancing antigen presentation. M1 macrophages are

enlarged and show increased membrane activity (especially
ruffling), increased formation of pseudopodia, and increased

pinocytosis (uptake of fluid droplets) (Fig. 18.15). They move more
rapidly in response to chemotactic stimuli and they are attracted by
many different chemokines. They contain increased amounts of
lysosomal enzymes and respiratory burst metabolites, and they are

more avidly phagocytic than normal cells. M1 cells produce greatly
increased amounts of nitric oxide synthase 2 (NOS2). As a result,
they kill intracellular organisms or tumor cells by generating high
levels of nitric oxide. The nitric oxide can destroy nearby tumor

cells and intracellular bacteria such as L. monocytogenes (Fig. 18.16).
IFN-γ-activated macrophages can also inhibit the growth of
intracellular bacteria by down-regulating their transferrin receptors
(CD71), degrading ferroportin, and by reducing the concentration

of intracellular ferritin, their major iron storage protein (Chapter 7).

FIG. 18.15 Stained cultures of mouse macrophages grown under
identical conditions: Left, Normal unstimulated macrophages. Right,
Macrophages activated by exposure to IFN-γ and acemannan. Note
the cytoplasmic spreading of the activated cells. These cells secrete
large quantities of cytokines and nitric oxide. Original magnification
×400. (Courtesy Dr. L. Zhang.)

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