Immunology part 2 (trans 2) Flashcards
COMPLEMENT SYSTEM
- Part of 2nd line of defense (inflammation, phagocytosis, complement)
- A set of proteins that play a role in cytolytic destruction of cellular antigens by specific antibody
- Most complement components are synthesized in the liver except C1 (intestinal epithelial cells); Factor D (adipose); C1, C2, C3, C4 are also synthesized by macrophages
Destruction of Complement Proteins
- Complement should be destroyed because it interferes with serological tests
1. Heat inactivation – heat the serum at 56C for 30 mins
2. Anticoagulant (ex: EDTA) – binds Ca2+ to make it unavailable; C1qrs (a trimolecular complex) is stabilized by Ca2+ so if C1 is destroyed, the complement is destroyed
3. Prolonged storage – complement is only present in fresh serum; aging serum destroys complement
clinical correlation
Hypocomplementemia – characterized by low levels of complement especially C3; clinically significant specially in diagnosing autoimmune diseases
C3: most abundant component of the complement system; used to detect hypocomplementemia
Complement activation pathways
- Classical Pathway – triggered after Abs bind to microbes or other Ags; component of the humoral arm of adaptive immunity because it involves Abs
- Alternate/Properdin Pathway – complement proteins are activated on microbial surfaces; component of the innate immunity
- Lectin Pathway/Mannan-binding Leptin Pathway – binding to terminal mannose on surface glycoproteins of microbes; component of the innate immunity
Classical pathway
- C1q is attached to the Fc fragment of antibody
- C1qrs cleaves C4 yielding C4a and C4b
- Activation of C2 yields C2a and C2b
- C4b + C2a => C4b2a (C3 convertase)
- C3 convertase converts C3 into C3a and C3b
- C4b2a + C3b => C4b2a3b (C5 convertase)
- C5 convertase converts C5 into C5a and C5b
- C5b + C6 + C7 + C8 = slow lysis
- C9 enters through pores in the surface of bacterial cell
- C5b + C6 + C7 + C8 + C9 (membrane attack complex /MAC) = rapid osmotic lysis
- *C5a - most potent anaphylatoxin; responsible for increased vascular permeability, pain induction, muscle contraction and inflammatory response
- *Recognition unit: C1qrs particularly C1q binds to Ab - stabilized by Ca2+
- *Activation unit: formation of C5 convertase - C4, C2, C3
- *MAC: C5-C9
Alternative pathway
- *note it bypasses C1, C4 and C2
1. Factor B is activated into Factor Ba and Bb (Factor Bb is the active form) with the participation of C3, factor D and Mg2+ ions
2. Factor Bb will cleave C3 into C3a and C3b and will combine with C3b to form C3bBb (C3 convertase of the alternate pathway)
3. C3bBb + C3b => C3bBb3b (C5 convertase)
4. Properdin (Factor P) – binds to C3bBb to prevent spontaneous decay of the complex
5. MAC
**recognition unit (does not require Abs):
- Bacterial cell walls (w/ LPS)
- Fungal cell walls
- yeasts
- viruses
- virally infected cells
- tumor cell lines
- some parasites
**activation unit:
C3 convertase - C3bBb
C5 convertase - C3bBb3B
**C5 convertase and even starting from C3 convertase is stabilized by properdin (increases half-life from 90 sec to minutes)
(Mannan-binding) lectin pathway
- Almost the same in classical pathway; difference is how they are triggered
- Activated by mannose groups of glycoprotein
- Effectors:
1. MBP/MBL – Mannan-Binding Protein/Lectin
2. MASP – MBP-Associated Serine Protease
- *recognition unit: MASP-1 complex attaches to mannose/mannan, glycoproteins on bacteria, yeasts viruses and some parasites
- *Activation unit: C5 convertase – C3b4b2a
- *Lectin has Ab-like activity that binds to CHO
- *Lectin pathway plays an important role in infants during loss of maternal Ab and acquisition of full-fledged Ab response to pathogens
MBL – binds to mannose or related sugars in Ca-dependent manner
Deficiency in MBL – common in infants w/ recurrent respiratory tract infections, otitis media and chronic diarrhea
what are the major biologic effects of complement?
1 . Opsonization - efficient phagocytosis
- Chemotaxis - C5a stimulates movement of neutrophils and monocytes toward sites of Ag deposition
- Anaphylatoxins - C3a and C5a can produce increased vascular permeability and smooth muscle contraction; C3a and C5a also stimulates mast cells to release histamine
- Cytolysis
Chemotaxins
C5a, C5b, C6, C7
Immune adherence
C3b
Kinin Activator
C2b
Anaphylatoxins
C3a, C4a, C5a (most potent)
Opsonins
C3b, C4b, C5b
Virus neutralization
C4b, C1
Plasma Complement Regulation
- C1 inhibitor (C1INH) – dissociates C1r and C1s from C1q
- Factor I – cleaves C3b and C4b
- Factor H – competes for Factor B; regulator of alternative pathway
- C4 binding protein – acts as a cofactor with I to inactivate C4b
- S protein (vitronectin) – prevents attachment of the C5b67 complex to cell membrane
- Decay accelerating factor (DAF) or CD55 – accelerates dissociation of C3 convertase
Inhibitors of MAC
- HRF – Homologous Restriction Factor
- CD59 or MIRL (Membrane Inhibitor of Reactive Lysis) – will act on MAC
clinical correlation
PNH or Paroxysmal Nocturnal Hemogobinuria
- Absence of CD55 and CD59
- Complement-mediated hemolysis
- Hemoglobinuria (due to destruction of RBCs) and hematuria may occur
- Nocturnal: named as such not because of night time but it is the shift of the pH of the body when we sleep
- The only acquired intrinsic normocytic hemolytic anemia; the rest are hereditary
- Usually patients develop myelodysplastic syndrome or preleukemia syndrome
Deficiencies of Complement Components
- C1 - LE-like syndrome
- C2 - LE-Like syndrome, recurrent infections
- C3 - severe recurrent infection
- C4 - lupus-like syndrome
- C5, C6, C7, C8 - Neisseria Syndrome
- C9 - no known disease
- C1INH - Hereditary Angioedema (HANE)
- DAF and HRF - Paroxysmal nocturnal hemoglobinuria
- Factor H or I - recurrent bacterial infections
Disorders of the immmune system
- Hypersensitivity
- Autoimmunity
- Immunodeficiency
- Amyloidosis
Disorders of the immmune system
Hypersensitivity
- a condition in w/c an immune response results in exaggerated or inappropriate reactions harmful to the host
- such reactions typically occur after the second contact with a specific antigen (allergen)
- the first contact is a necessary preliminary event that induces sensitization to that allergen
Disorders of the immmune system
Hypersensitivity: Type 1- IgE-Mediated Hypersensitivity/ Early Immediate Anaphylactic/ Immediate Hypersensitivity
Key characteristic: Fast response occurs within minutes
Initiation: 2-30 mins.
Mechanism: IgE found on mast cells cross link with antigen thus causing mast cells to degranulate releasing vasodilators (histamine)
Example: food and drug allergy, bee stings, systemic and local anaphylaxis, hay fever, asthma, eczema
Other notes:
o Wheal and flare reaction
o Can be systemic or localized (localized to a specific organ)
o Can cause anaphylactic shock which is lethal
o Food allergy may be as benign as rash and as serious as bee sting
Disorders of the immmune system
Hypersensitivity: Type 2- Cytotoxic Hypersensitivity/Antibody-mediated Cytotoxic Hypersensitivity
Key characteristic: Antibody directed against cell surface antigens mediates cell destruction via Antibody Dependent Cell mediated Cytotoxicity (ADCC) or complement
Initiation: 5-8 hrs.
Mechanism: IgG or IgM bound to cell surface antigens, with subsequent complement fixation. Produces direct damage to cell surface.
Test: direct and indirect Coombs test
Example: Blood transfusion reactions (Type A blood cell transfused into Type B blood causing Type A antibody to react to Type A blood cell), Hemolytic disease of the newborn (Erythroblastosis Fetalis), Autoimmune hemolytic anemia
Disorders of the immmune system
Hypersensitivity: Type 2- Cytotoxic Hypersensitivity/Antibody-mediated Cytotoxic Hypersensitivity
**Erythroblastosis fetalis where there is no problem with the first baby but the mother (Rh-) has developed immunity (Anti-Rh antibodies) on Rh+ baby. The second baby born has hemolysis which leads to elevated bilirubin levels. Unconjugated bilirubin has high affinity for fatty tissues so if bilirubin levels reach >20mg/dL, it binds to the neonatal brain (where most fat in babies are) thus causing kernicterus. Neonate undergoes phototherapy to conjugate bilirubin to water soluble form.
To prevent Erythroblastosis fetalis, mothers are injected with rhogam (antibodies that eliminate Rh+ RBC in maternal blood)
- May be caused by Rh (no problem with first child or ABO (problems can arise in first child)
- Do coombs test to check
Hypersensitivity: Type 2- Cytotoxic Hypersensitivity/Antibody-mediated Cytotoxic Hypersensitivity
Autoimmune Hemolytic Anemia
4 types:
Warm agglutinin (70%) *Agglutinin aka antibody
Cold agglutinin (antibodies that work best at 4oC)
Mixed agglutin
Paroxysmal cold hemoglobinuria : upon exposure to cold, there is hemoglobinuria
*In this type of hemolytic anemia, the body thinks that there is an intruder when in fact there’s none (autoimmune). They consider some of the normal cells as non-self.
Hypersensitivity: Type 3 - Immune Complex Mediated Hypersensitivity
Key characteristic: immune-complex reactions
Initiation: 2-8 hrs.
Mechanism: Antigen- antibody complexes deposited at various sites induces mast cell degranulation via Fc gamma RIII; PMN degranulation damages tissue
Example: Arthus Reaction (local reaction), systemic reactions disseminated rash, arthritis, glomerulonephritis, systemic lupus erythromatosus
Hypersensitivity: Type 4 – Delayed/Cell-mediated Hypersensitivity
Key characteristic: delayed hypersensitivity reactions, cell-mediated immunity, mediated by T-cells
Initiation: 24-72 hrs
Mechanism: Memory TH1 cells release cytokines that recruit and activate macrophages.
Example: Contact dermatitis, tubercular lesions, organ transplant rejection
Other notes:
o Opposite of type I
o First three types are humoral, only Type 4 is cell-mediated.
o Tuberculin test will be positive on people infected or vaccinated with M. tuberculosis, swelling on part of skin tested.
o Corneal transplant – organ least likely to have a transplant rejection due to absence of blood supply
AUTOIMMUNITY
Breakdown of the immune system’s ability to discriminate between self and non-self
Persistent activation of immunologic effector mechanisms that alter the function and integrity of individual cells and organs
Involves a defect in the T-suppressor cells which regulate the immune response
Occurs more commonly in females
2 Prototype Autoimmune Diseases: Systemic Lupus Erythematosus and Rheumatoid arthritis
Autoimmune diseases
Organ specific
o Thyroid – Hashimoto’s thyroiditis, primary myxedema, thyrotoxicosis
o Stomach – pernicious anemia (failure of the gastric parietal cells to produce intrinsic factor which will absorb Vitamin B12 that is essential for erythropoiesis)
o Adrenal – Addison’s disease
o Pancreas – Juvenile rheumatoid arthritis
Non-organ specific o Muscles – Dermatomyositis o Kidney – Systemic Lupus Erythematosus o Skin – Scleroderma o Joints – Rheumatoid arthritis
Autoimmune diseases
Etiologic Factors
Genetic – HLA (eg. HLAB27 in ankylosis spondylitis), inheritance, sex (higher risk in females)
Age – peak at 60 – 70 y/o
Exogenous – UV rays, drugs, viruses, chronic infection, altered antigens (perceived as non-self)
Immune complex deposition (eg. glomerulonephritis)
Complement activation – release of mediators of inflammation
Autoimmune diseases
Immunogenic stimuli
Hidden / sequestered Antigens - antigens that don’t normally circulate in the blood / fails to establish immune tolerance
Altered antigens arise because of mutation
Foreign antigen shared or cross reactive w/ self antigens or tissue components which may lead to confusion to establish self from non-self
Autoimmune diseases
Main autoantibodies
Anti-GBM antibody (Glomerular Basement Membrane)
ANA (Antinuclear antibody) – seen in SLE
Anti platelet Abs = Idiopathic Thrombocytopenic Purpura (ITP)
o Acute type – in children
o Chronic type – in adults
Anti-Smith – seen in 1/3 of SLE cases
Anti-sperm – sperm is considered as foreign, results in inability to conceive in females; so they can’t conceive baby
Anti-phospholipid antibody syndrome (APAS) – able to conceive but fail to maintain pregnancy until the 3rd or 4th month because the baby is considered as non-self
Autoimmune diseases: SYSTEMIC AUTOIMMUNE DISEASES
- Systemic Lupus Erythematosus
- Scleroderma
- Rheumatoid Arthritis
SYSTEMIC AUTOIMMUNE DISEASES:
Systemic Lupus Erythematosus
Disease of the connective tissue
Expresses itself as a vasculitis (inflammation of blood vessels)
It is an IMMUNE COMPLEX disease characterized by overproduction of AUTOANTIBODIES (DNA-antiDNA complexes – most important of the immune complexes formed)
Arthritis is the most common manifestation
Also manifests itself by skin lesions, “butterfly rash/ RED WOLF’ (red rash across nose and cheeks – malar rash)
SYSTEMIC AUTOIMMUNE DISEASES:
Systemic Lupus Erythematosus
- *4 out of 11 criteria to confirm diagnosis of SLE
- *may be present simultaneously or successively within a given observation period:
1) Discoid rash
2) Oral ulcer
3) Photosensitivity
4) Arthritis
5) Malar/butterfly rash
6) Immunologic disorder
7) Neurologic disorder
8) Renal disorder
9) Anti-nuclear Antibody (ANA)
10) Serositis (inflammation of serous fluids)
11) Hematologic disorder
SYSTEMIC AUTOIMMUNE DISEASES:
Systemic Lupus Erythematosus
- Laboratory Observations
- Anti-Nuclear Antibodies (ANA) – most striking feature, although not diagnostic of SLE
- LE cell – PMN leukocyte with ingested LE body (a homogenous cytoplasmic mass that often fills the cytoplasm of the phagocyte)
- Often, LE bodies are not engulfed by neutrophils producing “rosette formation”
- LE FACTOR: a 7s IgG antibody which reacts with DNP (deoxyribonucleoprotein) and complement - Hypocomplementemia
- Hypergammaglobulinemia
- Depletion of suppressor T cells (which allows overproduction of autoantibodies)
SYSTEMIC AUTOIMMUNE DISEASES:
Scleroderma
Auto-centromere Antibody (ACA) – highly selective for the CREST variant of scleroderma
o C – calcinosis cutis
o R – Raynaud’s phenomenon (gangrenous necrosis of the distal part of the extremities due to cold exposure)
o E – esophageal dysmotility
o S – sclerodactyly (taut, shiny, inelastic skin of the fingers causing difficulty in mobility)
o T – telangiectasia (capillaries become dilated, often with spidery appearance)
SYSTEMIC AUTOIMMUNE DISEASES:
Rheumatoid Arthritis
Autoimmune disease causing chronic joint inflammation and periarticular tissue swelling
Etiology: genetic, hormonal, immunologic, infectious
Chronic, progressive (in contrast to gouty arthritis which is acute and episodic)
Bilateral, symmetrical
3 or more joints affected, usually the hands
May also present with malar rash and oral ulcers
Involves pannus formation
SYSTEMIC AUTOIMMUNE DISEASES:
Rheumatoid Arthritis
**Osteoarthiritis (OA)
A degenerative disease found in the elderly
**Gouty Arthritis
Characterised by increased levels of uric acid (hyperuricemia)
Presence of Tofus
More common in males and presents itself as an acute episodic disease
SYSTEMIC AUTOIMMUNE DISEASES:
Rheumatoid Arthritis - Rheumatoid Factor
o Group of immunoglobulins that interact specifically with the Fc portion of IgG molecules (anti-antibodies) o Primarily, are of the IgM class o Presence of RF alone does not confirm diagnosis of RA. Although presence of RF is not consistent with RA, the presence of polymorphonucleocytes (neutrophils or PMN) in inflamed joints is observed in all stages of the disease. These cells, as well as macrophages and other immune cells comprise the cellular infiltrate resulting in release of cytokines, radicals, and enzymes which participate in the destruction of a joint
SYSTEMIC AUTOIMMUNE DISEASES:
Rheumatoid Arthritis - Felty’s syndrome
Complication of rheumatoid arthritis that is characterized by splenomegaly, leukopenia, and presence of HLA DR4
IMMUNODEFICIENCY
- Primary or Congenital Immunodeficiency Diseases
2. Secondary or Acquired Immunodeficiency Diseases
IMMUNODEFICIENCY:
Primary or Congenital Immunodeficiency Diseases
Defect is intrinsic to immune system
Usually a genetic defect that leads to decreased number or function of cells of immune system
Nitroblue Tetrazolium Test (NBT)
o Used to identify phagocytic defect
o Normal cells reduce NBT to blue-black formazan dye
o In CGD, NBT is not reduced to blue-black color
Primary or Congenital Immunodeficiency Diseases
DiGeorge Syndrome
Disorder:
Characteristics:
Primary or Congenital Immunodeficiency Diseases
DiGeorge Syndrome
Disorder: T lymphocyte
Characteristics: Thymic hypoplasia (underdevelopment of thymus gland); facial deformities; patients present with current infection
Primary or Congenital Immunodeficiency Diseases
X-linked agammaglobulinemia
Disorder:
Characteristics:
Primary or Congenital Immunodeficiency Diseases
X-linked agammaglobulinemia
Disorder: B lymphocyte
Characteristics: No gamma globulins (immunoglobulin portion of plasma); no antibodies because they are in the gamma fractions
Primary or Congenital Immunodeficiency Diseases
Wiskott Aldrich
Disorder:
Characteristics:
Primary or Congenital Immunodeficiency Diseases
Wiskott Aldrich
Disorder: T lymphocyte and B lymphocyte
Characteristics: Immunodeficiency, thrombocytopenia, eczema
Primary or Congenital Immunodeficiency Diseases
Chronic Granulomatous Disease (CGD)
Disorder:
Characteristics:
Primary or Congenital Immunodeficiency Diseases
Chronic Granulomatous Disease (CGD)
Disorder: Phagocytic
Characteristics: Failure to kill catalase-positive bacteria (staphylococcus); normal levels of immune cells but phagocytic cells have defect in cytochrome b-558 => failure to produce H202 and O2
**Patient presents with deep pyogenic infection (pus-producing)
Primary or Congenital Immunodeficiency Diseases
Chediak-Higashi Syndrome
Disorder:
Characteristics:
Primary or Congenital Immunodeficiency Diseases
Chediak-Higashi Syndrome
Disorder: Phagocytic
Characteristics: Defective intracellular killing
Primary or Congenital Immunodeficiency Diseases
Job’s Syndrome
Disorder:
Characteristics:
Primary or Congenital Immunodeficiency Diseases
Job’s Syndrome
Disorder: Phagocytic
Characteristics: Defective mobility of phagocytes but random movement is normal
Primary or Congenital Immunodeficiency Diseases
Lazy Leukocyte Syndrome
Disorder:
Characteristics:
Primary or Congenital Immunodeficiency Diseases
Lazy Leukocyte Syndrome
Disorder: Phagocytic
Characteristics: Both random and directed mobility are defective; failure to respond to chemotactic stimuli
Primary or Congenital Immunodeficiency Diseases
C2 deficiency C3 deficiency PNH (Paroxysmal nocturnal hemoglobinuria)
Disorder:
Characteristics:
Primary or Congenital Immunodeficiency Diseases
C2 deficiency C3 deficiency PNH (Paroxysmal nocturnal hemoglobinuria)
Disorder: Complement
Characteristics: -
IMMUNODEFICIENCY:
Secondary or Acquired Immunodeficiency Diseases
Defect induced by external factors such as viruses, malignancies and drugs
E.g. AIDS
T and B assays
- Ficoll-Hypaque Technique
2. B and T-cell Function Tests
T and B assays:
Ficoll-Hypaque Technique
o Uses nylon wool to separate B- and T-cells (density gradient sedimentation)
T and B assays:
B and T-cell Function Tests
B-cell Function Test
Assess individual immunoglobulin levels IgG>IgA>IgM>IgD>IgE
B-cell under magnification: surface immunoglobulin’s
T-Cell Function Test
Hypersensitivity test and skin test (to check for drug allergies before administration)
T-cell under magnification: rosettes
TUMOR MARKERS
Tumor Surveillance
- Tumor Markers are substances produced by healthy cells but in cases of Cancerous cells their numbers are bolstered
- Any high concentration of Tumor Markers can be construed as a sign of a budding cancer state
- May be invaded by oncofetal agents (e.g. AFP); seen only in fetal/embryonic stage
May be used to convince the patient to undergo a procedure, especially when they are still asymptomatic.
Measuring these can also be done to demonstrate the efficacy of therapeutic procedures
Tumor Markers: (to diagnose tumors but are not meant to replace biopsy)
- Alpha-Fetoprotein Tumor Marker (AFP)
- Carcinoembryonic Antigen (CEA)
- Human Chorionic Gonadotropin (HCG)
- Prostate-Specific Antigen (PSA)
- Cancer Antigen 125 (CA - 125)
TUMOR MARKERS
Alpha-Fetoprotein Tumor Marker (AFP)
Cancer type: Liver cancer
TUMOR MARKERS Carcinoembryonic Antigen (CEA)
Cancer type: Colorectal cancer and breast cancer
TUMOR MARKERS
Human Chorionic Gonadotropin (HCG)
Cancer type: Choriocarcinoma & Testicular cancer
Source: chorionic villi which is a part of the immature placental tissues
TUMOR MARKERS
Prostate-Specific Antigen (PSA)
Cancer type: Prostate cancer
Has a long half-life
- Researchers must be aware of this when measuring the marker for Therapeutic efficacy
- While it may take time to clear the tumor marker, the cause of the proliferation of the substance may have already been fixed
TUMOR MARKERS
Cancer Antigen 125 (CA - 125)
Cancer type: Ovarian cancer
TRANSPLANTATION IMMUNOLOGY
- Autograft
- Syngraft
- Allograft / Homograft
- Xenograft / Heterograft
TRANSPLANTATION IMMUNOLOGY
Autograft
Transplant of an organism’s part within the same organism
Safest with the least chance of rejection
TRANSPLANTATION IMMUNOLOGY
Syngraft
Transplant between two genetically related organisms
Getting a syngraft from a twin is the best example as opposed to getting a syngraft from a sibling
TRANSPLANTATION IMMUNOLOGY
Allograft / Homograft
Transplant between two organisms not genetically related but similar species
Most of the graft used
TRANSPLANTATION IMMUNOLOGY
Xenograft / Heterograft
Transplant between two organisms of entirely different species
A baboon heart was already transplanted into a human who survived for a while but died of an infection later on
o Not a mechanical or surgical failure, just infection
o Anatomically you could survive with a baboon’s heart
