Page 637 - Veterinary Immunology, 10th Edition

defensive enzyme since by removing tryptophan it prevents the
VetBooks.ir growth of Toxoplasma gondii, Chlamydia pneumoniae, streptococci,

and mycobacteria.

Tolerogenic Dendritic Cells

The function of dendritic cells is to capture and process foreign
antigens for presentation to T cells. However, the precise signals
generated by dendritic cells depend on their state of maturity, on

their co-stimulating molecules, and on the presence or absence of
inflammatory cytokines. Thus proteins from dead and dying cells
that are captured by immature dendritic cells in the absence of
inflammation may cause the dendritic cells to kill responding T
cells or cause the T cells to differentiate into Treg cells. Treatment of

dendritic cells with IL-10 can block their ability to activate Th1 cells
while preserving their ability to promote Th2 responses.

Regulatory B Cells

A subpopulation of B cells may secrete IL-10, IL-35 and TGF-β. As a
result, they suppress the functions of Th17, Th1, and effector T cells
and induce the differentiation of Treg cells.

Natural Suppressor Cells

Natural suppressor (NS) cells are large granular innate
lymphocytes that produce cytokines with Treg-inducing activity.
They suppress B and T cell proliferation as well as immunoglobulin

production. NS cells occur normally in the adult bone marrow and
neonatal spleen and possibly regulate innate immune responses.

When Do Regulatory Cells Work?

Regulatory cells control almost all aspects of immunity. Treg cells,

for example, work constantly throughout an animal's life to prevent
self-reactivity. They are responsible for lack of immune responses in
the newborn; immunosuppression following trauma, burns, or

surgery; prevention of autoimmunity; and some cases of
hypogammaglobulinemia. Regulatory cells are found in some

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