Page 567 - Veterinary Immunology, 10th Edition

VetBooks.ir Macrophage Activation

When macrophages attack and ingest invading bacteria, they
produce enzymes and oxidants that assist in the killing process.

This response, however, may be insufficient to kill some invaders.
For example, bacteria such as L. monocytogenes, M. tuberculosis, and
Brucella abortus, and protozoa such as Toxoplasma gondii, can survive
and multiply inside normal macrophages. Antibodies are
ineffective against these organisms, so protection against this type

of infection requires additional macrophage activation (Fig. 18.12).
Activated macrophages are functionally polarized. Classically
activated or M1 macrophages are proinflammatory effector cells.

Alternatively activated or M2 macrophages have antiinflammatory
effects and play a role in tolerance induction and in resolving
inflammation.

FIG. 18.12 Normal macrophages are killed by growing intracellular
bacteria. IFN-γ and IL-2 released by Th1 cells can activate
macrophages and enable them to kill otherwise resistant
intracellular bacteria.

Classical Macrophage Activation

Macrophages become fully activated in two stages. Initial activation
is triggered by exposure to PAMPs and DAMPs from invading
bacteria and damaged tissues as described previously. Dendritic

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