Page 291 - Veterinary Immunology, 10th Edition

VetBooks.ir Other Antigen-Processing Cells

Naïve T cells require prolonged close interaction with DCs before
they can respond to antigens. Once primed, however, these T cells

may be further activated by relatively brief interactions with two
other major cell types: antigen-presenting macrophages and B cells.

Macrophages

Macrophages are the most accessible and best understood of the

antigen-processing cells. Their properties are described in Chapter
6. Once antigens are taken up by macrophages, a portion is
processed and presented to sensitized T cells. Macrophages,
however, are unable to engage in prolonged interactions with T

cells. As a result, they cannot activate naïve T cells. In addition,
antigen processing by macrophages is inefficient since much of the
ingested antigen is destroyed by lysosomal proteases and oxidants.
Indeed, macrophages and B cells can be considered cells with other

priorities (some call them “semiprofessional” antigen-processing
cells).

B Cells

B cells, like macrophages, cannot undertake prolonged interactions
with T cells. They do, however, have antigen receptors that enable
them to bind and process large amounts of specific antigen. They
ingest and process antigens before presenting them, in association
with MHC class II molecules, to sensitized T cells (see Fig. 15.7). B

cells probably play a minor role in antigen processing in a primary
immune response but a much more significant one in a secondary
response when their numbers have greatly increased and T cells are

easier to stimulate.

Other Cells

T cells may also be activated by many different “nonprofessional”
cell types. These include neutrophils, eosinophils, basophils, T cells,

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