Page 581 - Veterinary Immunology, 10th Edition

VetBooks.ir Innate Helper Cells

Innate helper cells perform functions that were once thought to be
performed only by helper T cells. Thus there are innate

counterparts of Th1 cells, Th2 cells, and Th17 cells. Each population
is characterized by their cell surface antigens, the signals that
trigger their production, by their transcription factors, as well as
their products and their effects. These innate lymphoid cells play an
important role in the very early stages of antimicrobial immune

responses. They also contribute to tissue repair and defense and the
maintenance of epithelial integrity on body surfaces. They are
classified into three groups. Group 1 defends against viruses,

intracellular bacteria and parasites. Group 2 defends against
helminths, and group 3 promotes immunity to intracellular
bacteria.

Group 1 Innate Lymphoid Cells

Group 1 ILCs are found under body surfaces such as the intestinal
mucosa, where they are scattered through the lamina propria. They
arise from lymphoid stem cells through the use of the transcription
factor T-bet. Group 1 ILCs produce large amounts of Th1-associated

cytokines such as interferon-γ and TNF-α in response to activation
by IL-12, -15 and -18 from dendritic cells (cDC1 cells) (Fig. 19.2). As
a result, they activate macrophages. They differ from natural killer
(NK) cells in that they cannot produce perforins and so are not

cytotoxic. ILC1 cells are essential for defense against viruses,
intracellular bacteria and protozoa, and some cancers through their
production of IFN-γ and TNF-α. As a result, they also antagonize
type 2 responses.

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