Allografts, Autoimmune Diseases and Amyloidosis

Normal immune response• Protection against infectious disease

Innate immunity• epithelial barriers • phagocytic neutrophils and macrophages• natural killer (NK) cells• plasma proteins (complement, clotting, kinin)

Adaptive immunity— “the immune response”• cellular

– B-cells and plasma cells– helper (Th) and cytotoxic (CTL) T-cells

• humoral– antibodies– cytokines

Pattern recognition receptors• DCs and macrophages respond to pathogen-associated

and damage-associated molecular motifs• Toll-Like Receptors (10 in human)

membrane receptors on outer plasma membrane and vessicles TLR2 for Gram positives, TLR3 for fungi, TLR4 for Gram

negatives, TLR9 for viral and bacterial DNA (CpG)

• NLRs (NOD-like receptors) (at least 20) Cytosolic proteins bind a variety of microbial products NLRC-type have caspase activation domain NLRP-type have pyrin domain

• Both classes of receptors activate caspases and NF-kB• Affect gene expression via NF-kB and MAP kinase

cascades• Release IL-1 and other proinflammatory cytokines

Lymphocytes and Receptors• 70% Tcells—TCRs recognize MHC-Ag complexes

CTLs express TCR dimer complexed with , CD3 and CD8• Ag must be bound to Class 1 MHC; universally expressed

– HLA-A, HLA-B, HLA-C heterodimer with 2 microglobulin– Ag is peptide processed in cytoplasm by proteasome from intracellular

microbe (B,V) or tumor-associated protein

Th cells express TCR dimer complexed with , CD3 and CD4• Ag must be bound to Class 2 MHC; restricted to DC, M, B-cells

– HLA-DP, HLA-DQ, HLA-DR – dimer– Ag is lysozome-processed peptide from extracellular microbe (B,E)

• 20% Bcells—surface IgM or IgD recognize soluble Ag complexes with Ig, Ig

• 10% NK cells—inhibitory receptors recognize MHC1-Ag complex; activating receptor must also bind ligand NKG2-CD94 heterodimer binds HLA-E, which is highly conserved KIRs (killer-cell immuglobulin-like receptor) bind HLA-A, -B or –C,

which are polymorphic

Ag and activation receptors

Ag receptor diversityLymphocyte receptors• One receptor per cell• Expression from one cmsm• Sommatic rearrangement • Several to hundreds of

segments (VDJC) per locus• Two rearranged gene loci

TCRs are or• 1 dimer per receptor

BCRs (Ig) are H-L• 2, 4, or 10 dimers per

functional unit

• Millions of receptors within each individual

MHC (human leukocyte antigen)

• Many receptors per cell• Expression from both cmsm• No rearrangement• Tens to hundreds of alleles

per locus• Three primary class Ia

chains all dimerize with same 2-microglobulin

• Class Ia HLA-A, -B, -C• Class Ib HLA-E, -F, -G, -H

• Six primary class II dimers

• HLA-DP, -DQ, -DR

• Thousands of receptor combinations throughout the population

Hypersensitivity Reactions

• Initial exposure to antigen results in sensitivity• Repeat exposure may result in pathologic

hypersensitivity• Both exogenous and endogenous antigens may

elicit hypersensitivity • Hypersensitivity is an imbalance between control

and activation of effector lymphocytes• Development of hypersensitivity is often

associated with the inheritance of particular susceptibility gene (HLA or linked to HLA)

Types of hypersensitivity reactions

• Type I — immediate (allergies, anaphylaxis) immunologic reaction occurs within minutes of antigen

binding to antibody bound to mast cells in individuals with prior sensitization

• Type II — Ab reaction to bound Ag caused by antibodies that react with antigens present

on cell surfaces or in the extracellular matrix

• Type III — Ab complex with circulating Ag antigen-antibody complexes deposited on vessel

walls cause inflammation and tissue damage

• Type IV — delayed-type initiated by antigen-activated (sensitized) T cells

Type IV hypersensitivity

• Initiated by antigen-activated (sensitized) T cells

• Delayed-type hypersensitivity (DTH) CD4+ Th1 cell cytokines stimulate

inflammation and recruit macrophages induced by environmental and self-antigens

• Direct cell cytotoxicity CD8+ CTLs cause tissue damage frequently follow viral infections

• Many autoimmune diseases are type IV hypersensitivities

Allograft rejection--kidney

Allograft rejection and self restriction

• Solid organ transplant tissue typing is limited to HLA-A, -B, -DR, more recently also -DQ

• Rejection requires recognition of Ag-MHC complex by host Tcells Genuine CTL reactivity to HLA-C Genuine Th reactivity to HLA-DQ, -DP Cross reactivity to similar alleles Molecular mimicry of pathogen to host-MHC—graft-Ag

complex may provide initial sensitization

• Limitations of methods for tissue typing Serological methods limited to Ab availability PCR-SSP limited to known sequence specificity Mixed Lymphocyte Reaction takes days (live donor)

Common transplants• Blood transfusions

To temporarily restore blood volume• Kidney

Living donors can be used because they have two kidneys and can get along with only one

• Lungs Usually transplanted along with a heart--attempts have been made with

portions of lungs from living donors• Liver

For irreversible liver failure (e.g., from toxins, hepatitis B infection); occasionally taken from living donor

• Heart For patients with failing hearts often because of inherited defects

• Pancreas For Type 1 diabetes mellitus

• Skin For burns; usually taken from elsewhere on the patient's own body

• Cornea To restore sight; taken from cadavers

• Bone marrow To repopulate hematopoietic stem cells after cancer treatment or SCIDS

Graft rejection• Hyperacute

Preformed Ab cross react with graft HLA—instant complement activation, thrombosis, ischemia

• Acute—DTH Cellular rejection

• Delayed-type hypersensitivity mediated by T-cells that recognize graft MHC

Vascular rejection• Th-cell stimulated Ab secretion damages graft vascuature

• Chronic Arteriosclerosis stimulated by growth factors released by Th

cells and macrophages

• Graft vs. Host disease—hematopoietic transplant Donor T-cells recognize recipient MHC and attack Uncommonly possible with liver transplant

Immune Tolerance

• Specific non-reactivity resulting from previous exposure to an antigen

• Active antigen-dependent process

• Tcell tolerance more enduring than Bcell

• Tolerance may be induced to non-self Ag

• Tolerance should develop naturally to self Central tolerance during maturation Peripheral tolerance neutralizes “escapees”

Induction of tolerance to non-self

• Important for natural development of tolerance or ignorance of proteins from environmental and commensal sources

• Allergy shots!

• Increasing amounts of foreign Ag administered s.c. or orally (not in US)

• Strategy is to promote Th1 and Treg responses to prevent class-switching in newly sensitized Bcells from IgG to IgE

Specific Immunotherapy

Central self tolerance Bone marrow

• Self-reactive BCRs deleted or rearranged again• Pro-Tcells migrate to thymus

Thymus• Autologous Ag expression induced in thymic

epithelium• Self-reactive clones deleted

Peripheral self tolerance Anergy (lack of activity)

• Failure of coreceptor engagement prevents activation

• TCR coreceptors CD28—CD80 or 86 (aka B7)• BCR coreceptor CD21 or CD40

Supression• Treg (formerly supressor Tcells) secrete factors

that down-regulate activity; IL-10, TGF Activation-induced apoptosis

• Fas on Tcells binds FasL on APC along with TCR-MHC and coreceptor-ligand interactions

• Death receptor activation of caspase-8, apoptosis

Immune disorders

• Allergies and atopy Atopic individuals express much more IgE

than normal Th2 skew promotes class-switch to IgE System is primed to respond quickly to very

small amounts of allergen Severe hyperresponsiveness leads to

anaphylaxis and shock

• Autoimmune disorders Imbalance between control and activation of

effector lymphocytes

Features of autoimmune diseases

• Persistence and progression epitope spreading from tissue damage

• release self-antigens and exposure of epitopes normally concealed from the immune system

• tolerance not developed against hidden epitopes

• Th1 responses cause destructive macrophage-rich inflammation and antibodies that activate complement and bind Fc receptors

• Th17 responses dominated by neutrophils and monocytes

Systemic autoimmune diseases• Systemic Lupus Erythmatosis (SLE)

Type III immune complexes to soluble self Ag

• Rheumatoid arthritis Type III immune complexes in synovial fluid

also DTH with fibrinoid necrosis and erosion

• Seronegative spondyloarthropathies DTH against ligaments

• Sjogren syndrome DTH against lacrimal and salivary glands

• Scleroderma DTH against ECM or smooth muscle

Systemic Lupus Erythmatosis (SLE)

• Antinuclear antibodies (ANAs) dsDNA histones nonhistone proteins bound to RNA (RNPs)

• Smith antigen

nucleolar antigens• Centromeres, topoisomerase

• Blood cell-directed antibodies red cells, platelets, lymphocytes

• Antiphospholipid antibodies Directed to phospholipid-bound serum proteins Prothrombin, annexin V, protein S, protein C Hypercoagulability results

Rheumatoid arthritis

• Chronic inflammation affecting mainly small joints

• Caused by unknown self antigen(s)

• DTH T-cell reaction with production of cytokines that activate phagocytes that damage tissues and stimulate proliferation of synovial cells (synovitis)

• TNF antagonists are of great benefit

• Antibodies (rheumatoid factors) contribute to the disease—Type III hypersensitivity

Figure 5-23 Rheumatoid arthritis. A, A joint lesion. B, Low magnification reveals marked synovial hypertrophy with formation of villi. C, At higher magnification, dense lymphoid aggregates are seen in the synovium.

Sjogren syndrome

Sjögren syndrome affects primarily the salivary and lacrimal glands, causing dryness of the mouth and eyes.The disease is believed to be caused by an autoimmune T-cell reaction against an unknown self antigen(s) expressed in these glands, or immune reactions against the antigens of a virus that infects the tissues.

Systemic sclerosis (scleroderma)• Cutaneous involvement (scleroderma) is

presenting symptom appearing in ~95% of cases

• Visceral involvement of the GI tract, lungs, kidneys, heart, and skeletal muscles (systemic sclerosis) produces the major morbidity and mortality

• Diffuse scleroderma progresses to viscera rapidly

• Limited scleroderma often confined to fingers and face Involvement of the viscera occurs late Also called CREST syndrome

• calcinosis, Raynaud phenomenon, esophageal dysmotility, sclerodactyly, and telangiectasia

Normal skin v. scleroderma

Immune deficiency diseases• Primary immunodeficiencies

Genetic defect affecting a primary component of humoral or cellular immunity

• X-Linked agammaglobulinemia (Bruton's agammaglobulinemia)• Isolated IgA Deficiency • Hyper-IgM Syndrome• DiGeorge Syndrome (Thymic Hypoplasia) • Severe Combined Immunodeficiency (SCID)• Immunodeficiency with Thrombocytopenia and Eczema (Wiskott-

Aldrich Syndrome)• Genetic Deficiencies of the Complement System

• Secondary immunodeficiencies Sequelae to infection, cancer, other diseases

• AIDS

AIDS and HIV• Properties of HIV

nontransforming human retrovirus lentivirus family

• HIV-1 associated with AIDS in the US, Europe, and Central Africa

• HIV-2 principally in West Africa and India

• Structure of HIV spherical with electron-dense, cone-shaped core

• major capsid protein p24• nucleocapsid protein p7/p9• two copies of genomic RNA (gag,pol,env,tat,rev,vif,nef,vpr,vpu)• three viral enzymes (protease, reverse transcriptase, and

integrase) lipid envelope derived from the host cell membrane

HIV Infection and AIDS

• Infection targets and destroys CD4+ Tcells surface gp120 binds CD4 molecules and

changes conformation CD4-bound gp120 binds coreceptor CCR5

(on Th, DC, m) or CXCR4 (on Th), altering shape again, exposure of gp41 peptide

hydrophobic peptide of gp41 inserts into target cell membrane resulting in fusion

HIV genome enters the cytoplasm of the cell integrating into nuclear genome during replication

Progression• Acute phase (weeks)

Mucosal memory T cells infected via CCR5 Symptoms of viral infection Steady-state viremia (set-point viral load)

• Chronic phase (years) Dissemination of virus to Th via DC in lympoid tissues Replication and destruction of T cells in lymph nodes Gradual inversion of CD4-CD8 balance

• Crisis phase (months) Viremia, fever, fatigue, secondary infections of Euk

pathogens (fungi, helminths, protozoa) Viral tumors develop in absence of effective Tcell

defense

Amyloidosis

• Deposition of proteinaceous aggregates in extracellular spaces

• Nonbranching protein -pleated sheet fibrils that bundle into fibers

• Associated proteoglycan and glycosaminoglycan units (P component) bind dyes like starch

• 23 different proteins have been identified in amyloid deposits

Accumulations

• Some accumulation of misfolded proteins is normal

• Normal accumulations cleared by m• Amyloid deposits not cleared due to defect

in m enzymes

• Protein mutations could result in greater tendency to misfold

• Protein mutations could result in resistance to proteases

Amyloid differs from collagen

• Lack of cellularity in amyloid hyaline areas relative to collagen-rich areas

• Appears less fibrous than collagen under low power

• Stains macroscopically with iodine and acid (like starch)

• Stains microscopically with Congo red

• Congo red staining of amyloid demonstrates apple-green birefringence under polarized light

Congo-red stained liver, normal light

Same slide under polarized light

Clinicopathologic Category Associated Diseases Major Fibril Protein

Chemically Related Precursor Protein

SYSTEMIC (GENERALIZED) AMYLOIDOSIS

Immunocyte dyscrasias with amyloidosis (primary amyloidosis)

Multiple myeloma and other monoclonal plasma cell proliferations

AL Immunoglobulin light chains, chiefly λ type

Reactive systemic amyloidosis (secondary amyloidosis)

Chronic inflammatory conditions AA SAA

Hemodialysis-associated amyloidosis Chronic renal failure Aβ2m β2-microglobulin

Systemic senile amyloidosis ATTR Transthyretin

HEREDITARY AMYLOIDOSIS

Familial Mediterranean fever   AA SAA

Familial amyloidotic neuropathies (several types)

ATTR Transthyretin

LOCALIZED AMYLOIDOSIS

Senile cerebral Alzheimer disease Ab APP

Endocrine A Cal Calcitonin

Medullary carcinoma of thyroid  Type 2 diabetes AIAPP Islet amyloid peptide

Islets of Langerhans  AANF Atrial natriuretic factor

Isolated atrial amyloidosis

Clinical features and symptoms

• Renal involvement proteinuria leading to the nephrotic syndrome

• Cardiac amyloidosis insidious congestive heart failure conduction disturbances and arrhythmias

• Gastrointestinal amyloidosis asymptomatic; or malabsorption, diarrhea,

and disturbances in digestion

Spleen