Pathology of Immunity Flashcards
Pre-existing defense against pathogens
Innate Immunity
Specific, programmed defense in response to antigen presence
Adaptive Immunity
Components of Innate Immunity
- Barrier defense (like skin)
- Cells
- Neutrophils
- Dendritic cells
- NK cells
•Proteins
- Complement
Components of Adaptive Immunity
•Lymphocytes
•Lymphocytes
- Antibodies
Physical/Chemical Barriers of Innate Immunity
- Salivary glands - secretions cleanse oral cavity (chemical)
- Skin and mucosae - form a physical barrier
- Tears - bathe the conjunctivae (chemical)
- Ciliated epithelium - protects lung mucosa
- Acid pH of stomach- kills microorganisms (chemical)
Pattern Recognition Receptors
important for innate immunity
- Toll like receptors
- NOD-like receptors and the inflammasome
- C-type lectin receptors
Complement Pathway Effector Functions
- C5a, C3a
- C3b
- MAC
- C5a, C3a = inflammation
- C3b = Phagocytosis
- MAC = lysis of microbe
3 Important things to remember about innate immunity
- Nonspecific
- Present at birth
- Does not alter with antigenic exposure
Adaptive Immunity: Tissues
- Generative organs?
• Bone marrow
- generation of lymphocyte stem cells.
- B lymphocyte maturation
• Thymus
- Maturation of T lymphocytes
Adaptive Immunity: Tissues
- Peripheral organs/tissues?
• Lymph nodes
- Lymphocytes can interact with APC’s and antigens in circulating lymph
•Spleen
- Lymphocytes can interact with blood- borne antigens
• Mucosa-associated lymphoid tissues (tonsils, adenoids, Peyers patches)
- Allow lymphocytes and plasma cells to be in the vicinity of antigens within the mouth and intestinal tract
• Primary site of hematopoiesis, starting in embryonic period
• Origin of stem lymphocytes
- B cell maturation
Bone Marrow
What does the Medulla of the thymus contain?
- Maturing T lymphocytes
- Dendritic APC’s with high levels of MHC I and II molecules
- Hassall corpuscles: SQUAMOUS CELL NESTS
In lymph nodes, APC’s interact with lymphocytes and you get?
- T and B cell clonal expansion
- B cell differentiation into plasma cells
- Migration of T cells and plasma cells out of lymph nodes and into circulation
Where in the lymph nodes do T and B cells predominate?
- T cell = paracortex
- B cells = germinal centers
Function of B lymphocytes?
- Neutralization of microbe
- Phagocytosis
- Complement activation
Function of Helper T lymphocyte
- Activation of macrophages
- Inflammation
- Activation (proliferation and differentiation) of T and B lymphocytes
Function of Cytotoxic T Lymphocyte (CTL)
Killing of infected cell
Function of Regulatory T Lymphocytes
Suppression of immune response
Function of Natural Killer cells
Killing of infected cell
MHC Class I
- Type of cells?
- Typically recognize?
- Antigens are processed into peptides by the ?
- Mode of transportation?
- Presentation of the entire complex to ?
- All nucleated cells (and platelets)
- Intracellular antigens (viral, tumor)
- Proteasome
- Peptides transport to the endoplasmic reticulum, load into the groove of MHC, and the entire complex migrates to the surface
- CD8+ (cytotoxic) T cells
MHC Class II
- Type of cells?
- Typically recognize?
- Antigens are processed into peptides by the ?
- Mode of transportation?
- Presentation of the entire complex to ?
- Antigen presenting cells
- Extracellular antigens (bacterial, allergens)
- Endolysosomal enzymes
- Vesicles form with processed peptides and MHC II complex
- CD4+ (helper) T cells
Extensive heterogeneity of HLA haplotypes is important for?
- Differences in fighting off illness
- Differences in allergic sensitivities
Clinical Important of HLA Haplotypes
- Transplanted organs
- Associated autoimmune diseases
Cell-mediated immunity
- APC’s bring back intracellular pathogens while expressing MHC-associated peptide antigens
- Recognition by T cells:
- Proliferation
- Differentiation
- Migration
- Killing
• Dendritic cells capture microbial antigens from epithelia and tissues and transport the antigens to lymph nodes. During this process, the DCs mature, and express high levels of MHC molecules and costimulators. Naive T cells recognize MHC-associated peptide antigens displayed on DCs. The T cells are activated to proliferate and to differentiate into effector and memory cells, which migrate to sites of infection and activate the phagocytes to kill the microbe; other subsets of effector cells enhance leukocyte recruitment and stimulate different types of immune responses. CD8+ CTLs kill infected cells harboring microbes in the cytoplasm. Some activated T cells remain in the lymphoid organs and help B cells to produce antibodies, and some T cells differentiate into long-lived memory cells
MHC class I evoke the killing of?
INTRACELLULAR pathogens by CD8+ cells
MHC class II evoke a response to?
EXTRACELLULAR pathogens by CD4+ RECRUITMENT of macrophages and other T lymphocyte subsets
Humoral Immune Response
• Mediated by antibodies • Antibodies come from plasma cells, which come from B lymphocytes • Can be: - T-cell independent - T-cell dependent ~ Isotype switching ~ Increasing affinity
• Naive B lymphocytes recognize antigens, and under the influence of TH cells and other stimuli, the B cells are activated to proliferate and differentiate into antibody-secreting plasma cells. Some of the activated B cells undergo heavy-chain class switching and affinity maturation, and some become long-lived memory cells. Antibodies of different heavy-chain classes (isotypes) perform different effector functions
Mediators for Class Switching in the humoral immune response
IFN-Y and IL 4
What part of the humoral immune response do Helper T cells get involved with
- Affinity maturation
- Memory B cell
First Ig produced and a large pentamer?
IgM
doesn’t cross the placenta
Ig with the longest half life and important in fetal protection
IgG
Ig with mucosal defense and present in high levels in colostrum
IgA
- Ig with the shortest half life
- Regulates hypersensitivity reactions
- High affinity binding to FC receptor on Mast cells, basophils, eosinophils
IgE
Functions of NK cells
• Innate lymphoid cells
- No TCR or Ig
- Destroy stressed and abnormal cells
- Turned off with MHC class I expression
What activates NK cells?
- Damages cells (recognized by NKG2D receptors)
What inhibits NK cells?
- Self MHC molecules
- Class I MHC (present on all nucleated cells)
What is clonal selection and immunologic tolerance?
- Lymphocytes are killed if they recognize self antigens (clonal deletion)
- On introduction of a pathogenic antigen, the particular lymphocytes specifically targeted against that antigen are preferentially activated and produce identical cells
How does antigen receptor diversity occur?
B and T cell receptors (BCR and TCR) are products of multiple germline and randomized somatic genetic programming
What if a large population of cells with the exact same genes is identified?
- Abnormal clone
- Neoplasia
- Lymphoma
An immune reaction to foreign or self antigens that are excessive and harmful
Hypersensitivity reactions
Which does Type I hypersensitivity involve?
recognize on sight
• Seasonal allergies • Asthma • Food allergies •Severe allergic reactions - Urticaria (hives) - Angioedema - Anaphylaxis
Type I Hypersensitivity:
- DC’s present antigens to?
- T cells differentiate to ?
- B cells class-switch to ?
- Naive T cells
- Th2 cells
- IgE
Type I Hypersensitivity:
What interleukins are involved?
- IL- 4: class switching
- IL- 5: Eosinophil activation
- IL- 13: Enhanced IgE production
Type I Hypersensitivity:
What do mast cells do?
Get prepared by binding IgE to their very specific FCERI receptor
Type I Hypersensitivity: Mast Cell Activation
• Degranulation of?
• Lipid mediators?
• Cytokines and chemokines?
- Histamine
- Lipid Mediators
- Leukotrienes B4, C4, D4
- Prostaglandin D2
- Platelet activating factor
• Cytokines and chemokine
- Leukocyte recruitment (late phase)
Immediate Response for Type I Hypersensitivity
Mast cell mediators –>
- Vasodilation
- Vascular leakage
- Smooth muscle spasm
Late Phase Reaction for Type I Hypersensitivity
Inflammatory cells –>
- Eosinophils, basophils, neutrophils
- Leukocyte infiltration
- Epithelial damage
- Bronchospasm
Reactions of Type I Hypersensitivity
- Bronchoconstriction
- Increase bowel peristalsis
- Increase vasodilation permeability
Food antigen-driven disease of childhood (food allergy for Type I hypersensitivity)
Eosinophilic esophagitis
Symptoms of Eosinophilic esophagitis
- Recurrent dysphagia
- Weight loss
- Can’t swallow effectively
- Hurts to swallow
What should doctors do when they encounter a Type I reaction?
- DIAGNOSE that an allergic reaction is happening
- TREAT the allergic reaction
- Block Histamine
- Airway support
• IDENTIFY the allergen
Steps for Skin-prick Testing
- IgE bound to mast cells
- Injected allergen binds to IgE molecules
- IgE cross-linking activates mast cells
- Vasodilation, increased interendothelial spaces: Redness and swelling
Reaction where antibodies directly react with antigens present on the cell surface or extracellular matrix
- Autoantibodies
- Exogenous antigens that are bound to cell surfaces
Type II Hypersensitivity Reaction
What are the 3 mechanisms for Type II?
- Opsonization and PHAGOCYTOSIS
- Complement and Fc receptor-mediated INFLAMMATION
- Antibody-mediated CELLULAR DYSFUNCTION
Type II:
Autoimmune Hemolytic Anemia
- Target Antigen ?
- MOD?
- Antigen: Red cell membrane proteins (Rh blood group antigens, I antigen)
- MOD: Opsonization and phagocytosis of red cells
Type II:
Autoimmune Thrombocytopenic Purpura
- Antigen: Platelet membrane proteins (GpIIb: Illa integrin)
- MOD: Opsonization and phagocytosis of platelets
Type II:
Pemphigus Vulgaris
- Antigen: Proteins in intercellular junctions of epidermal cells (epidermal cadherin)
- MOD: Antibody-mediated activation of proteases, disruption of intercellular adhesions
Type II:
Vasculitis caused by ANCA
- Antigen: Neutrophil granule proteins, presumably released from activated neutrophils
- MOD: Neutrophil degranulation and inflammation
Type II:
Goodpasture Syndrome
- Antigen: Noncollagenous protein in basement membranes of kidney glomeruli and lung alveoli
- MOD: Complement- and Fc receptor- mediated inflammation
Type II:
Acute Rheumatic Fever
- Antigen: Streptococcal cell wall antigen; antibody cross-reacts with myocardial antigen
- MOD: Inflammation, macrophage activation
Type II:
Myasthenia Gravis
- Antigen: Acetylcholine receptor
- MOD: Antibody inhibits acetylcholine binding, down-modulates receptors
Type II: Graves Disease (hyperthyroidism)
- Antigen: TSH receptor
- MOD: Antibody-mediated stimulation of TSH receptors
Type II:
Insulin-resistant diabetes
- Antigen: Insulin receptor
- MOD: Antibody inhibits binding of insulin
Type II:
Pernicious anemia
- Antigen: Intrinsic factor of gastric parietal cells
- Neutralization of intrinsic factor, decreased absorption of Vitamin B12
Type II: Complement and Fc receptor-mediated inflammation Mechanism
• Mechanism = damaged tissue!
- Basement membrane proteins
- Streptococcal proteins that cross-react with myocardium
Rheumatic heart
- Type of hypersensitivity?
- What occurs?
• Type II
• Acute and chronic forms
• Cross reactive antibodies!
- Molecular mimicry *: Streptococcal antigen looks like myocardial antigen so you end up destroying heart tissue
Type II: Antibody-mediated cellular dysfunction Mechanism
• Mechanism: dysfunction due to receptor blockade!
- Disrupted endocrine signaling
- Disrupted neural signaling
Which Type II diseases are associated with opsonization and phagocytosis?
- Autoimmune hemolytic anemia
- Autoimmune thrombocytopenic purpura
Which Type II diseases are associated with complement and Fc receptor-mediated inflammation?
- Vasculitis causes by ANCA
- Goodpasture syndrome
- Acute rheumatic fever
Which Type II diseases are associated with antibody-mediated cellular dysfunction?
- Myasthenia gravis
- Graves disease (hyperthyroidism)
- Insulin-resistant diabetes
Type of hypersensitivity where antigen-antibody complexes FORM and DEPOSIT, causing DAMAGE
Type III Hypersensitivity
Steps for Type III Hypersensitivity
- Antibody combines with excess soluble antigen, forming large quantities of Ab/Ag complexes
- Circulating immune complexes become lodged in the basement membrane of epithelia in sites such as kidneys, lungs, joints, skin
- Fragments of complement cause release of histamine and other mediator substances
- Neutrophils migrate to the site of immune complex deposition and release enzymes that cause severe damage in the tissues and organs involved
Which type of reaction involves serum sickness and an Arthus reaction?
Type III
What is serum sickness?
- Acute is due to?
- Chronic due to ?
- Acute form classically due to non-human protein antigen (diphtheria antitoxin)
- Chronic form usually due to self-antigens (i.e. lupus)
What is a Arthus reaction?
Arthus reaction: local reaction
- Experimentally seen in rabbits injected with horse serum
- Rare local effect of vaccination
What type of test to you perform to help identify the disease process by the pattern of antibody deposition?
What is the process?
Immunofluorescence
- An anti-Ig antibody tagged with fluorescent dye is added to a sample. It binds to any antibodies present in the tissues being tested
What type of reaction has smooth, linear immunofluorescence?
Type II
What type of reaction has grainy, granular immunofluorescence?
Type III
Which type?
- In the heart, post-streptococcal cross-reactive antibodies DIRECTLY act on the myocardium
Type II
Which type?
- In the KIDNEY, post-streptococcal cross-reactive antibodies are forming immune complexes that deposit in the glomeruli
Type III
What occurs in Type IV?
T-cells turn!
•CD4+ response
- Cytokine release
- Inflammation
•CD8+ response
- Cytotoxic against Ag on surface of a target cell
Which disease do you REALLY REALLY need to associate with Type IV?
Type I diabetes mellitus
T cells destroy the insulin producing cells in pancreas
What is one hallmark of Type IV reactions?
Granuloma
- Presence of blobs in histo= giant cells with rim of nuclei around the periphery
Type IV:
What is caused by a variety of agents that are capable of inducing a PERSISTENT T cell-MEDIATED IMMUNE RESPONSE?
Immune granuloma
Type IV:
Rheumatoid Arthritis
- Specificity of Pathogenic T cells:
- Principle Mechanism of Tissue Injury:
- Clinicopathologic Manifestations:
• Specificity of Pathogenic T cells:
- Collagen?
- Citrullinated self proteins?
• Principle Mechanism of Tissue Injury:
- Inflammation mediated by TH17 (and TH1?) cytokines; role of antibodies and immune complexes?
• Clinicopathologic Manifestations:
- Chronic arthritis with inflammation, destruction of articular cartilage
Type IV:
Multiple Sclerosis
- Specificity of Pathogenic T cells:
- Principle Mechanism of Tissue Injury:
- Clinicopathologic Manifestations:
• Specificity of Pathogenic T cells:
- Protein antigen in myelin (e.g., myelin basic protein)
• Principle Mechanism of Tissue Injury:
- Inflammation mediated by TH1 and TH17 cytokines, myelin destruction by activated macrophages
• Clinicopathologic Manifestations:
- Demyelination in CNS with perivascular inflammation; paralysis
Type IV:
Type I diabetes mellitus
- Specificity of Pathogenic T cells:
- Principle Mechanism of Tissue Injury:
- Clinicopathologic Manifestations:
• Specificity of Pathogenic T cells:
- Antigens of pancreatic islet B cells (insulin, glutamic acid decarboxylase, others)
• Principle Mechanism of Tissue Injury:
- T cell-mediated inflammation, destruction of islet cells by CTLs
• Clinicopathologic Manifestations:
- Insulitis (chronic inflammation in islets), destruction of B cells; diabetes
Type IV:
Inflammatory bowel disease
- Specificity of Pathogenic T cells:
- Principle Mechanism of Tissue Injury:
- Clinicopathologic Manifestations:
• Specificity of Pathogenic T cells:
- Enteric bacteria; self antigens?
• Principle Mechanism of Tissue Injury:
- Inflammation mediated by TH1 and Th17 cytokines
• Clinicopathologic Manifestations:
- Chronic intestinal inflammation, obstruction
Type IV:
Psoriasis
- Specificity of Pathogenic T cells:
- Principle Mechanism of Tissue Injury:
- Clinicopathologic Manifestations:
• Specificity of Pathogenic T cells:
- Unknown
• Principle Mechanism of Tissue Injury:
- Inflammation mediated mainly by TH17 cytokines
• Clinicopathologic Manifestations:
- Destructive plaques in the skin
Type IV:
Contact sensitivity
- Specificity of Pathogenic T cells:
- Principle Mechanism of Tissue Injury:
- Clinicopathologic Manifestations:
• Specificity of Pathogenic T cells:
- Various environmental chemicals (e.g., urushiol from poison ivy or poison oak)
• Principle Mechanism of Tissue Injury:
- Inflammation mediated by TH1 (and TH17?) cytokines
• Clinicopathologic Manifestations:
- Epithelial necrosis, dermal inflammation, causing skin rash and blisters
What kind of reaction is the Mantoux test?
Delayed Type IV hypersensitivity
Tolerate self-antigens
Immunologic tolerance
Learned prior to release from generative lymphoid organs
Central tolerance
Ongoing regulation in peripheral tissues
Peripheral tolerance
Central Tolerance:
- What happens in the thymus?
- Production of T-cell receptors that cross-react with self-antigens are detected
- APOPTOSIS
Central Tolerance:
- What happens in the bone marrow?
- B lymphocytes may recognize self antigens
- RECEPTOR EDITING
- (or APOPTOSIS)
What happens in Peripheral tolerance?
- Anergy
- Suppression by Treg cells
Anergy:
What are the inhibitory receptors on T lymphocytes that help T cells down regulate when self antigens are present? (tumors and viruses use this to evade immune destruction)
- CTLA
- PD-1
What can we do for tumor immunotherapy?
Block PD-1 or CTLA-4 signaling
- By blocking this interaction with antibodies directed against PD-1 and CTLA, we can intensify the immune response against cancer cells
Most common Treg cells are?
- Induced by TGF-B
- Positive for CD4
- Express CD25 and FOXP3
What do FOXP3 Treg cells do?
Tell pregnant mom not to attack the baby’s antigens that are from the dad
What are the 4 mechanisms of peripheral self-tolerance?
- Normal response
- T cell anergy
- T cell suppression
- T cell deletion
Murphy’s law:
- A mutation in the AIRE gene can lead to ?
- Polyendocrine disorders due to autoimmunity
Murphy’s law:
- A autoimmune disease called IPEX can cause ?
- Systemic disease in humans
3 requisite factors for defining pathologic autoimmunity
- An immune reaction is directed against a self-antigen
- The immune reaction is primarily responsible for a pathologic condition
- There is no other pathophysiology responsible
Genetic and environmental contribution to autoimmune disease?
• Genetic
- Susceptibility genes
• Environmental
- Infection
- Damaged tissues
~ Epitope spreading
- Typically hereditary inflammatory conditions of the joints, particularly the spine
- Inflammation leads to degeneration and then fusion of the vertebrae
Ankylosing Spondylitis
Ankylosing Spondylitis is strongly associated with Class ?
Class I HLA allele B27 *
Crohn Disease
- Polymorphisms in the ? gene render Paneth cells in intestinal epithelium ineffective at microbial killing
- Defective killing and clearance allows accumulation of bacteria and an exaggerated immune response
NOD-2 (non-HLA)
NOD gene encodes ?
NOD-like receptor