Immunology: MHC and antigen presentation I MHC and antigen presentation II Peter A. Savage, Ph.D. Assistant Professor Department of Pathology PATH Cell Pathology / Immunology (Spring 2016) Thursday, April 7, 2016

taken from Hennecke et al., Cell 104:1, 2001 T cell receptor (TCR) peptide/MHC The TCR recognizes peptides displayed by MHC molecules hypervariable TCR  and TCR  CDR3 loops sit directly over peptide T cells recognize composite surface of peptide + MHC

Major antigen presenting cell (APC) types MHC class I molecules are expressed by all nucleated cells MHC class II molecules are primarily expressed by “professional” APCs

Nobel Prize in Physiology and Medicine, 2011 innate immunity and dendritic cells Ralph Steinman: discovery and characterization of dendritic cells

Identification of a novel cell type: dendritic cells “Identification of a novel cell type in peripheral lymphoid organs of mice. I. Morphology, quantitation, tissue distribution” Steinman and Cohn, JEM 137:1142, 1973 Large stellate cell type that adheres to plastic culture dishes These “dendritic cells” are potent at priming T cells in vitro large nucleus phase-dense mitochondria

Dendritic cells in lymph nodes, most DCs reside in T cell zones outside of B cell follicles

Populations of dendritic cells plasmacytoid DCs are a major source of Type I interferons during infections classical DCs are heterogeneous, and specialize in priming and coordinating T cell responses

Capture and display of microbial antigens

Capture and presentation of protein antigens by DCs Two types of conventional DCs: migratory DCs capture antigen in peripheral organs, then migrate to LNs resident DCs are pre-positioned in LNs and capture antigen draining through lymphatics

Two waves of antigen presentation by dendritic cells “Distinct dendritic cell populations sequentially present antigen to CD4 T cells and stimulate different aspects of cell-mediated immunity” Itano et al., Immunity 19:47, 2003 E  RFP = E  antigenic peptide (I-A b -restricted) fused to red fluorescent protein (RFP) Y-Ae = Monoclonal antibody specific for E  /I-A b complexes Inject E  RFP into mouse footpad, analyze draining lymph node cells presenting E  /I-A b complexes at early time points are resident DCs migratory DCs carrying E  RFP antigen from injection site arrive 24 hrs later

Distinct DC subsets are specialized to capture and present antigens in different contexts “Strategically localized dendritic cells promote rapid T cell responses to lymph-borne particulate antigens” Gerner et al., Immunity 42:172, 2015 Lymphatic sinus DCs (LS-DCs) in the lymph nodes capture particles draining from the lymphatics CD11c = DC marker CD169 = macrophage marker lymphatic sinus DCs positioned at sites of lymphatic drainage B = B cell zone M = medulla

Nobel Prize in Physiology and Medicine, 1980 Discovery and characterization of immune response genes immune response genes human HLA genes mouse MHC genes

The identification of genes dictating tumor and graft acceptance in mice “Methods for the study of histocompatibility genes” Snell, Journal of Genetics 49:87, 1948 Genetic basis for susceptibility to transplantable tumors (and tissue grafts) Developed series of inbred (genetically identical) mouse strains What are the dominant genes conferring acceptance of tumors derived from a given inbred strain? Several histocompatibility (H) loci were identified that allowed tumor acceptance H-2 locus was the strongest determinant of tumor acceptance / rejection

inbred strain E of genotype H/H challenge F2 offspring with H/H tumor derived from strain E different inbred strain of genotype h/h only mice of genotype h/h will reject tumor and survive mice with at least one copy of H will accept tumor and die cross surviving mice to H/H strain E and repeat! The identification of genes dictating tumor and graft acceptance in mice “Methods for the study of histocompatibility genes” Snell, Journal of Genetics 49:87, 1948

Genes of the major histocompatibility (MHC) locus The genes in the MHC locus are tightly linked and usually inherited together

Structure of class I and class II MHC molecules

Binding of peptides to MHC molecules

Nobel Prize in Physiology and Medicine, 1996 Specificity of cell-mediated immune defense (MHC restriction)

H-2 compatibility is required for T cell recognition of viral antigen “H-2 compatibility is required for T cell-mediated lysis of target cells infected with lymphocytic choriomeningitis virus” Doherty and Zinkernagel, JEM 141:502, 1975 Demonstration that T cells recognize viral peptides presented by self MHC molecules Challenge different inbred mouse strains with LCMV T cells from a given strain only lysed target cells from strains of the same H-2 haplotype

Properties of MHC molecules and genes

Features of peptide binding to MHC molecules

Pathways of intracellular processing of protein antigens

Class II MHC pathway of processing of internalized vesicular antigens

Class I MHC pathway of processing of cytosolic antigens This bottom pathway is referred to as “cross-presentation” because it involves the acquisition of exogenous antigen and presentation via the cytosolic MHC class I pathway

Cross-presentation of microbial antigens from infected cells by DCs

Viruses have evolved mechanisms to suppress antigen presentation “Herpes simplex virus turns off the TAP to evade host immunity” Hill et al., Nature 375:411, 1995 Herpes simplex virus (HSV) gene product ICP47 inhibits TAP-dependent peptide translocation assay for translocation of reference peptides into ER HSV infection blocks peptide translocation I-labeled peptides that are translocated to ER are glycosylated and retained... but not if HSV is ICP47-deficient adenovirus expressing ICP47 blocks peptide translocation

Features of the pathways of antigen processing

Role of MHC-associated antigen presentation in recognition of microbial antigens by CD4 + and CD8 + T cells

Demeter O’Reilly: a little girl who lost weight and became weak 15-month-old girl of Irish descent Developed weight loss, distended abdomen, diarrhea No family history of metabolic, neurologic, GI, or autoimmune disease Lab tests revealed anemia, normal blood cell counts, mild elevation of liver enzymes Tested positive for anti-endomysium IgA and anti-tissue transglutaminase IgA, suggestive of celiac disease Biopsies from duodenum revealed villous atrophy, crypt hyperplasia, increased IEL lymphocytes, confirming celiac disease diagnosis Family received extensive nutritional counseling and Demeter was started on gluten- free diet At 6-month follow-up, she had returned to good health Case 42: Celiac Disease

Celiac disease is caused by T cell recognition of modified gluten-derived peptides Requires presence of DQ2 or DQ8 class II HLA alleles

Celiac disease is caused by T cell recognition of modified gluten-derived peptides flattened mucosa crypt hyperplasia Case 42: Celiac Disease inflammatory infiltrate

Case 42: Celiac Disease Why do gluten-derived gliadin peptides induce celiac disease in some DQ2 + / DQ8 + subjects? Requires genetics (DQ2/DQ8), stimulus (gluten), and unknown environmental triggering Some proline-rich gliadin peptides are resistant to proteolysis (including 33-amino acid  2-gliadin peptide, which contains multiple epitopes) Undigested gliadin peptides pass through the GI lining into the subepithelial space Tissue transglutaminase (TTG) deamidates peptide, allowing binding to DQ2/DQ8 deamidation changes glutamine (Q) to glutamate (E) Presentation of modified peptides to CD4 T cells triggers pathogenesis

Case 42: Celiac Disease