Page 425 - Veterinary Immunology, 10th Edition

VetBooks.ir Memory T Cells

As described, when naïve T cells encounter antigens with
appropriate co-stimulation, they differentiate into multiple effector

T cell populations. These effector cells are usually short lived
because they are eliminated by apoptosis. However, some resist
apoptosis, and develop into long-lived memory cells. These can be
thought of as “antigen-experienced” cells. Memory T cells can be
the most abundant T cell population in the body, especially in older

animals since they accumulate throughout life. Compared to naïve
T cells, memory cells are easier to activate, live longer, and have
enhanced effector activity. As a result, they mount a strong rapid

cytokine response the next time they encounter the antigen and can
provide life-long protection against pathogens. The differences in
behavior between naïve and memory T cells likely results from
epigenetic modifications that alter gene transcription (mainly
histone methylation [Chapter 20]) and hence cell functions.

This development of effector and memory T cell populations
results from asymmetrical T cell division (Fig. 14.22). As described
earlier, naïve T cells interact with antigen-presenting cells for

several hours through an immunological synapse. Once it receives
sufficient stimulation, a T cell begins to divide even before it
separates from the antigen-presenting cell. The dividing T cell is
polarized since one pole of the cell contains the immunological
synapse and associated structures. The other pole contains

molecules excluded from the synapse. Thus when the cell divides, it
forms two distinctly different daughter cells. The daughter cell
adjacent to the synapse is the precursor of the effector T cells. The

daughter cell formed at the opposite pole is the precursor of the
memory T cells.

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