Page 408 - Veterinary Immunology, 10th Edition

be sustained for hours.
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FIG. 14.11 Successful stimulation of a T cell requires the additive
effects of multiple signals. Depending on the antigen, the T cell may
be activated by signals from multiple TCRs or by appropriate
costimulation.

The properties of a helper T cell are determined by the type of
antigen-presenting cell used and by the nature of the signals
received from it. Thus naïve T cells have strict requirements for
activation. They must receive a sustained signal for at least 10 hours
in the presence of co-stimulation or for up to 30 hours in its

absence. This level of co-stimulation can only be provided by
dendritic cells, which supply high levels of co-stimulatory and
adhesion molecules. In contrast, other antigen-presenting cells act

only transiently. Although macrophages and B cells can briefly
trigger a TCR, they are unable to complete the process and thus fail
to activate naïve T cells. Once primed, however, T cells require
about an hour to reach commitment. Only then can they be

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