Glycopathophysiology of immunity and inflammation 4/25/05

Large O-linked Glycosaminoglycans and poly-lactosamine structures Glycoprotein N-linked and O-linked oligosaccharides Glycolipid oligosaccharides

General Principles Cell-surface glycans participate in all arms of the immune system Glycan recognition is an integral component of innate (antibody-independent) immunity Specific glycan structures modify humeral immune (antibody-dependent) responses Differentiation of immune cell types requires appropriate glycan expression Cell-cell interactions that lead to immune cell activation are modulated by carbohydrate

Today’s topics Thymic selection of self vs. non-self Innate immunity Generation and function of the immune synapse Carbohydrate-dependent antibody structure Regulation of antibody production and B-cell responsiveness by glycan

Self vs. non-self selection What does restricted mean? MHC I, MHC II, Cd1d?

Core-2 synthesis generates ligands for Galectins

Galectin binding induces apoptotic signals

C2GlcNAcT activity in relation to thymic selection C2GlcNAcT expression by naïve T-cells in the thymic cortex increases with residence time and decreases as the differentiating T-cell migrates to the medulla Strong TCR activation by self-bound MHC results in retention of the naïve T-cell in the cortex and maintenance of C2GlcNAcT activity (negative selection) Weak TCR activation results in migration of the T-cell to the thymic medulla and down-regulation of C2GlcNAcT activity (positive selection) C2GlcNAcT activity generates substrates for Galectin binding, leading to apoptosis of cortical T-cells

Tissue surveillance leads to the activation of T-cells and the initiation of innate immune responses

Professional antigen presenting cells sit at the interface between innate and adaptive responses

Innate immunity first then discuss antigen presentation

Innate immune responses detect the presence of pathogen, or non-self molecular patterns--frequently these are glycans Caroff, M., 2002

Caroff, M., 2002

Caroff, M., 2002

Takeda, K., 2003

Activation of dendritic cells by various TLR ligands produces subsets of cytokines that activate adaptive responses Iwasaki, A., 2004

Antigen presentation and the adaptive immune response

After Varki, A.

How is antigen presented?

Glycans are essential for peptide loading onto MHC-I Rudd, P., 2001

The immunological synapse is the communication point for activation of specific T-cells Red/brown = cell adhesion molecules, integrins, Ig-CAM Green/yellow = TCR, MHC I/II White = outlines of T-cell on an APC Dustin, M., 2000

Dustin, M., 2000

The synapse must accommodate glycans Rudd, P., 2001

Galectins may organize components of the synapse, providing a regulatory matrix that modulates signaling levels--GlcNAcTV KO has overactive signaling Lowe, J., 2001

T-cell activation leads to altered O-linked glycan expression Tsuboi, S., 2001

Altered glycosylation of CD43 (leukosialin) modulates the synapse Tsuboi, S., 2001

T-cell activation modulates B-cell responses

Th1--IFNg, IL12, microbial responses, auto-immunity Th2--IL4, 5, 6, 9, 10, 13, parasite responses, asthma, allergy

IgG1 glycans are essential for antibody function Rudd, P., 2001

Under galactosylated IgG1 is recognized by MBP, leading to complement activation--mechanism of pathology in RA and SLE? Rudd, P., 2001

Sialic acid-recognizing Ig-superfamily lectins) Human Siglecs Sialic acid-recognizing Ig-superfamily lectins) Arg97 Trp2 Trp106 Neu5Ac G 4 MAG Glia 3 CD33 Myeloid Precursors Monocytes Macrophages A F 10x 1 Sialoadhesin Macrophage Subset V-set domain C2-set domain 2 CD22 B cells ?Basophils After Varki, A.

Three Possible Models for Functions of CD22-Sialic Acid Interactions Collins, B., 2002

Sialic acid-recognizing Ig-superfamily lectins) Human Siglecs Sialic acid-recognizing Ig-superfamily lectins) Human Siglecs (Sialic acid-binding Ig-superfamily lectins) ITIM ITAM Putative Tyr-based motif V-set domain C2-set domain 10x 1 Sialoadhesin Macrophage Subset 2 CD22 B cells ?Basophils 5 Neutrophils Monocytes 6 OBBP-1 Placenta B-cells 11 Macro- Phage 10 Eosinophils 9 Granulocytes T cell subset 8 SAF-2 7 AIRM-1 NK cells T cell subset CD33(Siglec-3)-related Siglecs 4 MAG Glia 3 CD33 Myeloid Precursors Monocytes Macrophages

B-cells and glycans Subsets of antibodies require appropriate glycosylation for function B-cell activation is modulated by carbohydrate-lectin interactions

General Principles Cell-surface glycans participate in all arms of the immune system, where they: Mediate or regulate cell adhesion Modulate cell signaling events By regulating signaling and adhesion, progenitor cells are driven toward specific differentiation/activation by glycan expression Immunoglobulins, especially, require specific N-linked glycans for stability and activity

xx

xx

General Principles 1 2 3 4 5 6