Ch 3 Day 2 (II)

Signal 1 for T Cells

• The necessary signal 1 for T cells is antigen recognition.

Innate Immune Response

• Toll-like receptors (TLRs) recognize different microbial products and stimulate the expression of costimulators and the secretion of cytokines in Antigen-Presenting Cells (APCs).

Costimulators and Cytokines

• Costimulators and cytokines work in concert with antigen recognition by the T cell to stimulate a response.
• Costimulators are expressed on the surface of APCs and provide a second signal to T cells.
• Cytokines are secreted by APCs and provide a third signal to T cells.

Mucosal Associated Invariant T (MAIT) Cells

• MAIT cells are specific for a limited set of microbial antigens presented by the non-polymorphic MHC class I-like molecule, MR1.

Recognition of Molecules

• A wide variety of molecules, including those displayed by class I–like molecules and those requiring no specific processing or display, are recognized by gamma delta T cells.

Proteins Produced in Cytosol

• Proteins produced in the cytosol of infected and tumor cells, or that enter the cytosol from phagosomes, bind to MHC class I molecules.

Displaying Peptides

• MHC molecules perform the function of displaying peptides derived from protein antigens.

Ensuring Specificity

• The recognition of microbial products by TLRs and other pattern recognition receptors ensures that T cells respond to microbial antigens and not to harmless, non-microbial substances.

Activation of APCs

• TLRs activate APCs to express membrane proteins (costimulators) and to secrete cytokines that provide signals that function in concert with antigens to stimulate specific T cells.

Test your knowledge on the functions of antigen-presenting cells beyond antigen display. Explore the roles of APCs in providing additional signals for T cell activation and the two-signal hypothesis of lymphocyte activation.