Antigen-presenting cells receptors

Ligands Small peptides associated with major histocompatabUity (MHC) proteins in the plasma membrane of macrophages and other antigen-presenting cells Receptors Single transmembrane a helix several protein kinases associated with cytosolic domain found only on T lymphocytes... 

Autoimmune Disease. Figure 2 Generation of autoreactivity. APC, antigen presenting cell IFN, interferon LPS, lipopolysaccharide MHC, major histocompatibility complex T, T-lymphocyte TCR, Tcell (antigen) receptor TLR, toll like receptors. For details see text. 

Class IIHLA molecules are expressed on the surface of antigen-presenting cells. They play a key role in presentation of processed linear peptide antigens of at least nine amino acids to T cells. Antigen is bound to the HLA antigen binding cleft formed by the a and 3 chains of the HLA class II molecule. This tri-molecular HLA-antigen complex binds in turn to the variable portion of the T-cell receptor. 

The T cell receptor is a clonotypic, T cell specific surface receptor that mostly recognizes peptides bound to MHC molecules on antigen-presenting cells. 

The development of effector T cells following activation by antigen-presenting cells also requires the interaction of another receptor-ligand pair. CD40 molecules on antigen-presenting cells are required to bind... 

Although closely related, monocytes/macrophages (MO) possess features that are distinct from DCs. Due to their limited expression of T-cell costimulatory molecules, MO are not able to prime T cells de novo, but rather stimulate effector/memory T cells by the secretion of cytokines, which support T-cell proliferation. As DCs, MO differentiate from myeloid precursors and form a heterogeneous population of antigen-presenting cells (APCs) that link the innate and adaptive immune systems. However, their ability to interact with T cells via MHC class II TCR interaction(s) as well as engagement of T-cell costimulatory receptors on their surface, makes close contact between MO and Tregs likely to occur in vivo. 

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