IMMUNOPATHOLOGY—Part 1: WARD
IF NOT TOLERANCE, THEN WHAT?
 AUTOIMMUNE DISEASES
o ORGAN-SPECIFIC
 Hashimoto disease: CD8+, CD4+ / IFN-g, ADCC (see p. 1169)
 AIHA
 Pernicious anemia
 Multiple sclerosis
 ITP
 Type 1 diabetes
 Myasthenia gravis
 Graves disease: abys to TSH receptor, thyroglobulin
o SYSTEMIC
 SLE
 RA
 Sjogren syndrome: multi-HLA linkage. Agn recognized by CD4+ T-cells
 Reiter syndrome: infection-generated abys
Goodpasture Syndrome
SUSCEPTIBILITY GENES
 Most autoimmune diseases have a strong genetic predilection
 Multiple susceptibility genes are involved, notably HLA genes
 No single gene indicted for any one disease
 Mutations / polymorphisms of Fas, others
INFECTIONS
 May upregulate expression of B-7 on APCs
o if latter present self-agn, activation of T-cells
 Some microbes may express agns with amino- acids similar to those of self-agns
o net result: activation of T-cells
o “molecular mimicry”(streptococcal myocarditis)
 Other microbes may release / alter self-agns
o net result: activation of T-cells
 Still others may produce cytokines and
o recruit potentially self-reactive lymphocytes
ANY MORE BAD NEWS?
 Once established: diseases are progressive, inexorable
 “Epitope spreading”: release and / or exposure of
o previously cryptic epitopes
 Continued recruitment of autoreactive T-cells
 Response is repetitive
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REALLY STARTED HERE!!!
SOURCES OF ANTIGENS & REACTIONS
 Exogenous: hypersensitivity
o environmental (dust, drugs)
o homologous (blood products)
 Endogenous (autologous): autoimmune
TYPE I HYPERSENSITIVITY
 In individuals previously sensitized to an antigen, an immunologic reaction occurs within
minutes of rechallenge, following combination of that antigen with antibody bound to mast
cels. Most often with vessels under mucosa.
 Immune response releases:
o vasoactive substances (Mast Cells)
 Vasodilation, leaky - tranudate
o spasmogenic substances
 Smooth muscles to contract – bronchoconstriction, some gut
o proinflammatory cytokines (recruit inflammatory cells)
 Recruit inflammatory cells (PMNs, eosinophils, basophils, macros into the
arena)
(ANAPHYLACTIC) – BIPHASIC!
 Previous sensitization...….
 Rechallenge: systemic/ local response, 5-30 / 60 mins
o Vasodilation
o Leakage
o smooth muscle spasm (location dependent)
o Increased glandular secretions (location dependent)
o shock / death if rechallenge is intravenous
 Late-phase reaction: 2-24 hours. Lasts several days
o Part Two
CHRONOLOGY
 Acute:
o histamine (increase: broncho-spasm, vascular permeability, secretion of glands
(make mucous))
o LTC4, LTD4 (vasoactive/spasmogenic)
 Intermission: setting the scene for Act II
o elaboration of LTB4 (by what cells?: strongly chemotactic, Mast cells and others),
PAF (Platelet activating factor), TNF-a = TNF
o intent: recruitment of inflammatory cells
 Late phase: onset 2-24 hours, duration: days
o arrival of inflammatory cells
o release of epithelium–damaging mediators/cytokines
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PRIMARY MEDIATORS
 Source: mast cell granules
 Products:
o biogenic amines: histamine (triple action – know them)
o enzymes: proteases, acid hydrolases  kinins, C3a (chemotactic, fraction of
complement)
o proteoglycans: heparin (mediates packaging in granules).
 Increases porosity of ecm in general
 Secretagogues (causes release of contents of Mast Cells) other than IgE (main thing
that causes release of Mast Cell granules):
o C3a, C5a, by direct binding (anaphylatoxins)
o IL-8 from MØs
o morphine derivatives – always ask about allergies
o Mellitin – bee sting
o Heat or cold temperature can elicit response
SECONDARY MEDIATORS
 Source 1: mast cells
o phospholipase A2 activity  arachidonic acid
 leukotrienes C4, D4 (>>> histamine), E4
 prostaglandin D2 (bronchospasm, secretion)
o platelet-activating factor (PAF). Multipurpose.
o cytokines: TNF, IL-1, -3, -4, -5, -6, GM-CSF
 Source 2: neuts, monos → LTB4
 Source 3: MΦs → inflammatory proteins (MIP-1a, -1b)
 Source 4: epithelial cells → IL-6, IL-8, GM-CSF
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LATE PHASE REACTION
 Primarily the consequence of cell recruitment by:
o leukotrienes, PAF, TNF-a, cytokines (from nucleus)
 Recruited cells: neuts, eos, basos, monos ,CD4+T-cells
o release additional waves of mediators including
 LTB4 (attract other neutrophils) , LTC4 PAF
o eos produce MBP (major basic protein) /ECP (eosinophil chemotactic protein) ,
damaging epithelia
o all amplify and sustain original inflammatory response
 WITHOUT MORE ANTIGEN
 Steroids blunt cell response
LOCAL ANAPHYLAXIS
 Atopy: genetically determined, HLAs – runs in families, proclivity for reactions
o localized anaphylaxis from inhaled or ingested allergens
 Frequency: 10% of population. Family hx in 50% (of 10%)
 Higher serum IgE levels in atopics than in non-atopics
 Candidate genes for familial predisposition in asthmatics
o 5q31: genes for cytokines IL-3, -4, -5, -9, -13, GM-CSF
 (5q minus syndrome = dysplastic syndrome)
o 6p: gene close to genes for HLA complex
o 11q13: gene for b chain of IgE receptor
 Higher numbers of IL-4-producing TH2 cells in blood
SYSTEMIC ANAPHYLAXIS
 Antisera, hormones, enzymes, drugs (e.g., penicillin)
 Sequence:
o itching, hives, erythema (redness of the skin)
o constriction of respiratory bronchioles, wheezing
o laryngeal edema, hoarseness
o vomiting, cramps, diarrhea
o laryngeal obstruction
o shock
o DEATH
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TYPE II HYPERSENSITIVITY
Mediated by antibodies directed against antigens already present on cell surfaces or in
extracellular matrix
Humoral response
Antibodies are directed against:
o intrinsic antigens on normal blood cell surfaces
 Phagocytosis or lysis
o adsorbed antigens (drugs) on RBC surfaces
o cell surface receptors
o basement membranes in Goodpasture Syndrome
 Two organ disease
 Glomerular (kidney)
 Alveolar (lung)
o What do these Abs do?
 Phagocytosis (cells)
 Lysis (cells)
 Dysfunction (receptors)
 Destruction (basement membranes)
HOW DO THE ANTIBODIES ELIMINATE CELLS?
 IgG or IgM antibodies react with red cell surface antigens
o acting as opsonins, promote phagocytosis by FcR (IgG)
o activate complement: C1-4-2-3/3b (IgG)
 C3b affixed to C3b-R also promotes phagocytosis
o promote formation of C5b-6-7-8-9 (killer complex) (IgM) (cold immune)
 drills holes in red cell bilayer causing lysis
o IgG = phagocytosis
WHERE ARE RED CELLS ELIMINATED?
 End-point: red cells have disappeared. Killing fields:
o extravascular (warm autoimmune hemolytic anemia–IgG)
 Spleen
 phagocytic
o intravascular (cold autoimmune hemolytic anemia–IgM)
 lytic
ANTIBODY VICTIMS
 RBC:
o AIHA (phagocytosis or lysis)
o transfusion reactions (lysis, intravascular)
o EBF (maternal IgG crosses placenta)
 WBC: agranulocytosis
 Platelets: thrombocytopenia
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ANTIBODY VICTIMS: TISSUE-BASED
 Goodpasture Syndrome
o Glomerular basement membrane
o Alveolar basement membrane
 Desmosomes (skin) in pemphigus vulgaris
o loosening of epithelial cells
o bulla formation
ANTIBODIES AGAINST RECEPTORS
 TSH hormone receptor (thyroid epithelium)
 Antibodies against TSH receptors on cells
o stimulate them — inducing
o hyperthyroidism (Graves disease)
 Acetylcholine receptor (motor end-plate)
o react with receptors in end-plates
 impairment of neuromuscular transmission
 result: myasthenia gravis
TYPE III HYPERSENSITIVITY
Circulating antigen-antibody complexes produce tissue damage by eliciting inflammation
at sites of deposition.
SOURCES OF ANTIGENS?
 Exogenous:
o Foreign proteins
o bacteria
o viruses
 Endogenous:
o trace antigens in blood (rare)
o antigenic determinants of cells
o antigenic determinants of tissue (more common)
IMPORTANCE OF COMPLEX SIZE
 Larger complexes removed daily by RES
o relatively harmless
 Intermediate or smaller complexes:
o more dangerous
o danger amplified by persistence due to:
 quantities formed
 overloading of RES
COMPLEX DEPOSITION: MECHANISM
 Bimodal:
o complexes formed in circulation filter out
 deposited in tissues, e.g., glomeruli
o complexing may also occur in situ
 after initial implantation of agn in glomeruli

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WHERE ARE COMPLEXES DEPOSITED?
 Bodywide
o when complexes are formed in blood
o Day 1: Introduction of protein antigen
o Day 7: Antibodies formed
 enter blood
 form complexes with still-circulating antigens
 start depositing in tissues
o Day 10: drama begins with
 fever
 urticaria
 lymphoadenopathy
 proteinuria
 Locally (kidneys, joints, skin [Arthus rxn], serosa)
o when complexes are formed in situ
HOW DO COMPLEXES CAUSE TISSUE DAMAGE?
 Activation of complement cascade
o formation of chemotactic factors esp.C5a (for pmns, MØs)
o release of anaphylatoxins (C3a, C5a) —  permeability
 Attracted cells activated by attachment to C3b & Fc receptors
o release of hellish brew (including enzymes, free radicals)
 Aggregation of platelets, activation of Hageman factor
o initiate microthrombus formation
 Net effect: glomerulonephritis, vasculitis, arthritis, serositis, etc.
ROLES OF COMPLEMENT FRACTIONS
 C3b: promotes phagocytosis of complexes (and organisms)
 C3a, C5a (anaphylatoxins): increase permeability
 C5a: chemotactic for neutrophils, monocytes
 C5-9: membrane damage or cytolysis
DURATION OF DISEASE
 Acute post-streptococcal glomerulonephritis
o short term, self-limited (ICs catabolized)
 Systemic lupus erythematosus (SLE)
o ICs formed in agn excess most likely to be deposited
o long-term, chronic IC disease
 Nature of antigens still unknown in
o membranous glomerulonephritis
o polyarteritis nodosa
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TYPE IV HYPERSENSITIVTY:
PRINCIPLES
 Hypersensitivity is cell-mediated:
o initiated by specifically sensitized T lymphocytes
 delayed reaction by CD4+ T-cells
 direct cytotoxicity by CD8+ T-cells
 Mounted in response to a variety of intracellular organisms
o tbc, viruses, fungi, protozoa, parasites
 Contact dermatitis
 Graft rejection
DELAYED HYPERSENSITIVITY
 Mantoux reaction:
o Patient previously sensitized
 8-12 hours: reddening & induration
 24-72 hours: peak reaction
 thereafter subsides
o Histology:
 “cuffing” of venules, veins; largely lymphocytes
 most lymphocytes are CD4+ variants (what variant?)
 edema due to exudation of fibrin (induration)
o Initial exposure to tbc bacilli
o Naive CD4 T cells recognize tbc peptides in association with
 class II molecules on monocytes or Langerhans cells
o CD4 T cells  TH1 cells (sensitized, memory cells )
o TH1 cells enter circulation. Stay there for years.
o Reaction to skin tuberculin causes positive Mantoux
OVERVIEW
 TH1 memory cells interact with
o agn on agn-presenting cells
 Activation follows (with subsequent proliferation)
 TH1 cells then secrete cytokines
o result: Mantoux rxn. or granuloma formation
GRANULOMA
 Granuloma formation:
o due to persistent or non-biodegradable agns (e.g., tbc)
o macrophages replace cuffs of lymphocytes in 2-3 wks
o macrophages become epithelioid
o form granuloma
o associated collar of lymphocytes
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CYTOKINES
 IL12: produced by otherwise inept Møs on first exposure
o drive THO to differentiate to TH1 cells
o induce IFN-g secretion by T-cells and NK cells
 IFN-γ: produced by T-cells and NK cells with
o activates hitherto inept macrophages
 markedly improved phagocytosis and killing
 increased expression of class II molecules
 secretion of PDGF ( fibrogenesis)
 secretion of TNF, IL-1 (  inflammation)
 production of more IL-12 (TH1 response amplified)
 IL-2: produced by TH1 cells
o causes autocrine and paracrine proliferation of T-cells
 includes TH1 cells and other bystander T-cells
 TNF: from TH1 cells. Act on endothelial cells:
o produce prostacyclin  vasodilation, increased flow
o produce IL-8, a chemotactic factor
o increase P-E-selectin expression (on endothelial cells)
 promote attachment of lymphocytes, monocytes,
o thereby promoting egress of both by diapedesis
ALLERGIC DERMATITIS
 This is an allergic,contact process
 not irritative as in exposure to detergents
 URUSHIOL — in poison oak, poison ivy
 Re-exposure (rechallenge) leads to:
o accumulation of TH1 cells in dermis (some CD8+ cells)
o migrate towards antigen in epidermis
 TH1 cells then release cytokines, damaging keratinocytes
 Formation of intraepidermal vesicles
MULTIPLE SCLEROSIS
 CD4+ TH1 cells react with autologous myelin agn i.e.
o myelin basic protein
 Demyelination is vasculocentric with
o paralysis
o ocular lesions
TYPE 1 DIABETES
 CD4+ TH1 cells react with insulin in b cells
 Insulitis (lymphoid)
o destruction of b cells
o hyperglycemia of diabetes
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T-CELL-MEDIATED CYTOTOXICITY:
LYSIS
 Sensitized CD8 + T-cells (cytotoxic T lymphocytes, CTLs)
o attack grafts (graft rejection)
o destroy virus-infected cells
 in cell, viral peptides associate with class I mols
 together move to cell surface as a complex
 TCRs of cytotoxic CD8+ T- cells recognize the complex
 lysis proceeds before viral replication is completed
 similar drama with tumor-associated antigens
MECHANISMS
 Perforin-granzyme-dependent killing by CTLs
o perforin drills holes  osmotic lysis
o injected granzyme activate caspases  apoptosis
 CTLs also express Fas-ligand
o promote apoptosis in Fas-expressing cells
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TRANSPLANT REJECTION
Recognition of “foreigness” achieved by heterogeneity of HLA proteins
Rejection may be
o cell-mediated (T-cell)
o humoral (B-cell)
T-CELL-MEDIATED 1 (DIRECT)
 CD4+ helper cells
o proliferate on exposure to class II HLA antigens
o are transformed to TH1 cells which cause
 increased vascular permeability
 localized accumulations of lymphocytes,MΦs
 CD8+ cells recognize class I HLA agns
o undergo differentiation to CTLs
o these then lyse grafted tissue (perforin/granzyme etc.)
 CD4 helper & CD8 CTLs are involved in allorecognition
o recognize class I, II HLA agns, B7-1 & 2 on dendritics
 in donor organs
 already moved to host lymph node
T-CELL-MEDIATED (INDIRECT)
 Host (recipient) T lymphocytes recognize graft agns AFTER presentation to hosts’ own
dendritic cells
 In effect, process similar to processing / presentation of
o microbial antigens
 Result is a delayed hypersensitivity reaction
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ANTIBODY-MEDIATED, HYPERACUTE
 Set-up: preformed abys already present
o from prior rejection of kidney
o multiparous women with anti-paternal HLA abys
o prior blood transfusions (wbc/plts are rich in HLA agns)
 Occurs immediately:
o abys react with and deposit on graft endothelium
o complement fixation is followed by an Arthus-like rxn
o thrombosis, ischemic death
o rare today with crossmatching
HYPERACUTE REJECTION: KIDNEY
 Gross:
o cyanosis of kidney with mottling, flaccidity
o mere few drops of bloody urine
 Micro:
o neutrophils in arterioles, glomeruli, vasa recta
o Ig and C deposited in arterial wall
o fibrinoid necrosis, thrombosis, outright infarction
ACUTE REJECTION: KIDNEY
 Patient not previously sensitized
 Occurs weeks, months, years after transplantation
 Usually follows cessation of immunosuppression
 Rejection:
o humoral (vasculitis)
o cellular (interstitial mononuclear infiltrate)
o combined
ACUTE HUMORAL REJECTION: KIDNEY
 Antibodies to donor HLA antigens
 Main injury is vasculitis with fibrinoid necrosis
 Thrombosis leads to ischemic necrosis
 Alternative lesion: cytokine-induced (see p.221)
o intimal thickening (fibroblasts, myocytes, MØs)
o resulting infarction or atrophy of kidney
NEXT SLIDE ONLY
 Less acute,more indolent vasculitis (humoral)
o marked thickening of intima
o contains:
 proliferating fibroblasts
 foamy macrophages
 few myocytes
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ACUTE CELLULAR REJECTION: KIDNEY
 Activated T-lymphocytes:CD4+ and CD8+
o interstitial (invade, damage tubules)
o intracapillary (glomerular, peritubular)
o subendothelial (“endothelitis”)
 Prompt response to immunosuppression therapy
 Cyclosporine toxicity may be superimposed
 Clue: increasing creatinine in early months
CHRONIC REJECTION: KIDNEY
 Vascular changes:
o dense intimal fibrosis, cortical arteries
o resulting ischemia, loss of glomeruli with
 interstitial fibrosis
 tubular atrophy
 Duplication of glomerular basement membranes
 Interstitial infiltrates include mononucs, pl. cells, eos
 Clue: increasing creatinine over 4-6 months
INCREASING GRAFT SURVIVAL: HLA MATCHING
 Intrafamilial kidney transplants:
o markedly improved outcome if class I agns matched
 Cadaveric renal transplants
o Class I matching modestly improves outcome
o additional class II matching definitely improves outcome
o even HLA-matched unrelated donors will differ somewhat
 minor differences still require immunosuppression
IMMUNOSUPPRESSIVE DRUGS (ISD) (2)
 Price of immunosuppression:
o Infections with opportunistic fungi, viruses
o Cancers
 EBV-induced lymphomas
 HPV-induced carcinomas
 Kaposi sarcoma
TRANSPLANTATION OF OTHER SOLID ORGANS
 Liver, heart not matched
 Space more important: takes precedence because:
o Little time for tissue typing
o Rejection is relatively mild, easily controlled
AVERTING UNTOWARD EFFECTS OF ISD
 Interrupting interaction between donor dendritic B7 and
o CD28 receptors on host T-cells
o achieved by giving binders to B7
 Giving recipient donor dendritic cells
o induce tolerance to donor alloantigens
o net result is chimerism
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TRANSPLANTATION OF HEMATOPOIETIC CELLS:
GENERAL
 Recipient first irradiated with lethal doses:
o to destroy malignant cells (leukemias)
o to create a graft bed in aplastic anemias
 Three major problems arise:
o GVH disease
o transplant rejection
o immunodeficiency
GVH: Graft vs. Host
 Precipitated when (donor) immunocompetent cells are transplanted into immunologically
crippled recipients
 Transplanted cells recognize host alloantigens
 Settings:
o transplantation of allogeneic bone marrow
o transplantation of organs rich in lymphocytes (liver)
o transfusion of unradiated blood
 Recipients are immunodeficient:
o a priori
o because of drugs or radiation
 Drama begins when:
o immunocompetent donor T-cells recognize host HLA agns
o CD4+ and CD8+ subsets become anti-host (sensitized)
 Prevent by matching HLAs in donor & host
 Even that may not be enough:
o because of other minor incompatibilities
ACUTE GVH REACTION
 Days to weeks post-transplant. Any organ involved.
o skin: major rashes with blisters, desquamation
o bile ducts: destruction leads to jaundice
o GIT: mucosal ulceration  bloody diarrhea
 Oddly, lymphoid infiltration is NOT HEAVY
 Damage caused by:
o sensitized CD8+ T-cells (cell toxicity)
o cytokines from sensitized donor T-cells
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CHRONIC GVH REACTION:
CLINICAL
 May follow acute syndrome or arise insidiously
 Extensive skin injury; loss of appendages, fibrosis
 Cholestatic jaundice
 Esophageal strictures
 Depletion of nodal lymphocytes
 Recurring, life-threatening infections
 Autoimmunity triggered in some:
o grafted CD4s react with host B-cells
o causing some to produce autoantibodies
AMELIORATION ?
 GVH eliminated by removing donor T-cells from graft
 Mixed blessing:
o grafts tend to fail
o leukemias tend to recur
 Some T-cells therefore appear necessary for:
o Engraftment
o control of leukemic cells (GVL effect)
REJECTION OF ALLOGENEIC B.M. TRANSPLANTS
 Mediated by host NK / T-cells surviving radiation
 Host NK cells react against allogeneic stem cells
o because stem cells lack self-MHC class I mols
o fail to deliver inhibitory signals to host NK cells
 Training donor NK cells to attack leukemic cells (GVL)?
o NK cells will not see self-MHC molecules
 therefore cannot be inhibited
 won’t cause GVH reaction
TRANSPLANT-INDUCED IMMUNODEFICIENCY
 Caused by:
o prior treatment (iatrogenic)
o myeloablative preparation for graft
o attack on host immune cells by donor cells
o delay in repopulation of host’s immune system
 Profound immunosuppression:
o opportunistic infections, especially CMID
AUTOLOGOUS STEM CELL TRANSPLANTS
 Candidate patients have certain tumors, e.g.
o breast cancer
o myeloma
 Stem cells harvested from blood. Cryopreserved.
 Intense chemotherapy, destroys tumor, stem cells.
 Cryopreserved stem cells reinfused
 No rejection of graft. No GVH!
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