Page 632 - Veterinary Immunology, 10th Edition

VetBooks.ir Regulation by the Innate Immune

System

The triggering of innate immune responses through pattern-
recognition receptors (PRRs) activates many pathways that affect
the adaptive immune responses. For example, signaling by most
PRRs activates the transcription factors, NF-κB and NF-AT. These

can then activate T and B cells. Stimulation of TLR4 can also induce
Th1, Th2, and Th17 responses. The cytosolic PRRs such as the RLRs
and NLRs can also activate Th1 responses and trigger CD8 +
cytotoxicity (Chapter 18). Thus if a virus infects dendritic cells and

is recognized by cytosolic PRRs, not only will it trigger a type I
interferon response but it may also trigger the production of
cytokines and other co-stimulators needed to activate T cells.

Th17 Cells

+
Naïve CD4 T cells differentiate into Th17 cells when exposed to IL-
23 supported by IL-21, IL-6 and TGF-β. Th17 cells play an
important role in host defense and are potent inducers of acute
inflammation (Fig. 20.14). Th17 cells are conventional small

lymphocytes that are abundant in mucosal surfaces. Their presence
in these surface tissues is regulated by the gut microbiota.

632