Immunity and amyloidosis Flashcards
The cell mediated hypersensitivity reaction
Type 4 hypersensitivity
Type 1 hypersensitivity examples
- Bronchial asthma
- Hay fever
- Allergic reactions like…
- Casoni’s test
- Theobald smith reaction
- PK reaction
- Schultz Dale phenomenon
- Anaphylaxis
- Atopy (hereditary allergy)
Allergic reactions that cause Type 1 hypersensitivity
- Allergic dermatitis
- Allergic rhinitis
- Food allergy
- Pollen allergy
Pathogenesis of type 1 hypersensitivity reaction
- Antigen ➡️ APCs ➡️
- T cells which activates TH2 cells:
A) IL-4:
IgE antibody production ➡️
B) IL-5 recruitment of eosinophils - Degranulation of ‘sensitised’ mast cells by IgE:
A) early phase reaction
B) late phase reaction
Early phase reaction of type 1 hypersensitivity reaction
Due to release of preformed mediators like histamine from sensitised mast cells within 30 minutes
- Vasodilation
- Increased permeability
- Bronchospasm
Late phase reaction of type 1 hypersensitivity reaction
Due to mediators that are formed later like leukotrienes, cytokines, chemokines Between 2-24 hours 1. Epithelial damage 2. Tissue destruction Most important cell is eosinophil
Stain for mast cell
Toluidine blue
Type 2 hypersensitivity
Example
Antibody mediated M. Myasthenia gravis B. Blood transfusion reactions G. Grave’s disease, Good Pasteur’s syndrome I. ITP, Immune haemolytic anaemia, IDDM R. Rheumatic fever H. Hyper acute graft rejection P. Pernicious anaemia, pemphigus vulgaris My blood group is Rh positive
Mechanism of type 2 hypersensitivity reaction
Antibodies which are directed against fixed antigen (cell surface or ECM/ basement membrane-Good Pasteur’s syndrome)
When the antigen of type 2 hypersensitivity reaction is attached to basement membrane
- Antigen combines with Antibody on basement membrane
- Complement activation
- C3a, C5a
- Neutrophil recruitment
- Release of enzymes from neutrophil
- Destruction of basement membrane
Good Pasteur’s syndrome
When antigen of type 2 hypersensitivity reaction is fixed on cell membrane
Antigen-Antibody complex can cause: 1. Destruction of target cells: A) opsonisation B) complement fixation 2. Dysregulation of the function of target cells in myasthenia gravis, Graves’ disease (type 5 hypersensitivity reaction)
Type 3 hypersensitivity reaction
Examples
Immune complex mediated S. Serum sickness, SLE H. HSP (Henoch Schonlein purpura) A. Arthus reaction R. Reactive arthritis (Yersinia) P. PSGN (post streptococcus glomerulo nephritis), PAN (Poly arteritis nodusa)
SLE is which type of hypersensitivity reaction
Both type 2 and type 3 hypersensitivity reaction
The haematological lesions are type 2
Whereas the visceral lessons are type 3
Pathogenesis of type 3 hypersensitivity reaction
The three phases: 1. Formation of immune complex 5-7 days 2. Deposition of immune complex 3. Immune complex mediated tissue injury A) complement activation B) activation of Hageman factor
The entire process takes in 10-14 days
Most pathogenic immune complex are
Small, medium sized
Most common sites of deposition of immune complex
Kidney, blood vessels, skin
Type 4 hypersensitivity reaction
Examples
Delayed type hypersensitivity reaction Cell mediated (T cell) 1. Granuloma formation 2. Tuberculin test and Lepromin test 3. Contact dermatitis 4. Acute and chronic graft rejection 5. Rheumatoid arthritis 6. Multiple sclerosis 7. Inflammatory bowel disease 8. Psoriasis 9. GVHD (graft v/s host disease)
Pathogenesis of type 4 hypersensitivity reaction in brief
Mediated by 1. CD4+ T cells Activation of T helper (TH-1) cells 2. CD8+ T cells Direct destruction of viral infected and tumour cells
Pathogenesis of type 4 hypersensitivity reaction through CD8+ T cells
Through:
- Fas-Fas ligand mechanism
- Perforin granzyme mechanism
Pathogenesis of type 4 hypersensitivity reaction through CD4+ T cells
Activation of TH1 cells
These T helper cells produce cytokines like:
1. IL-2
2. IL-12 (recruits lymphocytes)
3. IFN- gamma (Interferon-gamma)- granuloma formation
Components of innate immunity
- Epithelial barriers
- Phagocytic cells
- Dendritic cells
- Natural killer cells
- Other innate lymphoid cells
- Several plasma proteins like compliment system
MHC/ HLA
Their types and loci
Gene is located in chromosome 6 (short arm)
3 types:
1. A,B,C
3. (Encode for certain complement proteins like C2, C4, properdin, HSP)
2. DP, DQ ,DR
Difference between HLA class 1 and 2 on the basis of location in cells
Class 1 is located on all nuclear cells and platelets
Class 2 are only present on APCs (dendritic cells, endothelial cells, fibroblasts)
Difference between HLA class 1 and 2 on the basis of which T cells they bind to
Class 1 binds with CD8+ T cells
Class 2 binds with CD4+ T cells
Difference between HLA class 1 and 2 on the basis of structure
Class 1 MHC consists of: 1. Alpha 1,2,3 2. Beta 2 micro globulin Peptide binding site is between alpha 1 and alpha 2 Class 2 MHC consists of: 1. Alpha 1,2 2. Beta 1,2 The peptide binding site is between alpha 1 and beta 1
Difference between HLA class 1 and 2 on the basis of detection test
Class 1 is detected by allo-antisera test
Class 2 is detected by mixed lymphocyte reaction
Difference between HLA class 1 and 2 on the basis of relation to graft
Class 1 is involved in graft rejection
Class 2 is involved in GVHD
Uses of MHC
- Paternity testing
- Autoimmune disorders, like
HLA B-27 ankylosing spondylitis
HLADR3, DR4 diabetes mellitus - Transplantation
- Anthropological testing
Order of importance of different HLA wrt transplant matching
HLA DR > B > A
These 3 are the most important ones for matching
000 mismatch
No mismatch on A, B ,D
HLA matching is not required for which and all graft
- Liver
- Lung
- Cornea
Graft rejection types
- Hyperacute graft rejection
- Acute graft rejection
- Chronic graft rejection
Hyperacute graft rejection
Occurs within minutes of transplantation
Type 2 hypersensitivity reaction caused by preformed antibodies
Most commonly seen in kidney transplants
Causes of the presence of preformed antibodies in hyperacute graft rejection
- Previous blood transfusion
- Previous transplantation
- Multiparous women
- ABO and Rh incompatibility
Hyperacute graft rejection features
Gross:
Kidney becomes cyanosed, mottled, flaccid
Microscopic:
1. Microthrombi
2. Fibrinoid necrosis
3. Neutrophillic infiltrate in glomerular capillary plexus
Acute graft rejection
Two types:
1. Acute cellular rejection
2. Acute humoral rejection
Occurs within days or months (less than 6 months) of transplantation
Acute cellular graft rejection
It can be caused by CD4+ T cells or CD8+ T cells
Type 4 hypersensitivity reaction
Responds to increasing dose of immunosuppressants
Acute humoral graft rejection
Caused by anti donor antibody
Either type 2 (or type 3) hypersensitivity reaction
Does not respond to increasing dose of immunosuppressants
So treatment is B cell depleting agents
Acute cellular graft rejection microscopic features
Tubulointerstitial pattern (most common):
1. Tubulitis
2. Interstitial mononuclear inflammation
Vascular pattern:
Endothelitis
Acute humoral graft rejection microscopic features
- Fibrinoid necrosis
- Peritubular capillaries have a deposition of a complement breakdown product C4d
Therefore C4d is used as a marker acute humoral graft rejection
Chronic graft rejection
Occurs within months to years of transplant
Can be cell mediated (T cell) or antibody mediated
Can be type 2 or type 4 hypersensitivity reaction
Chronic graft rejection microscopic features
Glomerulopathy
- Duplication of glomerular basement membrane
- Glomerulo sclerosis
- Tubular atrophy
- Interstitial fibrosis
- Atherosclerosis of graft vessels
GVHD or grunt disease of animals
Usually seen after bone marrow transplant Type 4 hypersensitivity reaction Two types: 1. Acute 2. Chronic
Acute GVHD
Occurs within 6 months Affected organs: 1. Skin - rash (most affected) 2. GIT - bloody diarrhoea 3. Liver - cholestatic jaundice
Chronic GVHD
Occurs after 6 months Affects: 1. Skin - scleroderma 2. GIT - strictures 3. Liver - cholestatic jaundice
Eichwald Slimser effect is also called
Explain
Y-linked graft rejection
Usually seen when a male gives a graft to a female
Y chromosome has UT4 gene which encodes for a graft rejection protein
Complications of transplantation
1. Infections like A. cytomegalovirus CMV infection: (owl’s eye inclusions) - most common B. BK polyoma virus infection (decoy cells- intranuclear basophilic inclusions in PCT) 2. GVHD 3. Graft rejection 4. Increased risk of malignancy A. Squamous cell carcinoma (HPV associated) B. Non Hodgkins’s lymphoma (EBV) C. Kaposi’s sarcoma (HHV-8)
Best diagnostic features of kidney allograft rejection
Kidney biopsy
Examples of immunodeficiency disorders
- Bruton’s hypogammaglobulinemia
- DiGeorge syndrome
- Wiscott Aldrich syndrome
- SCID
- Common variable immuno deficiency CVID
- Isolated IgA deficiency
- Hyper IgE syndrome / JOB syndrome
- Hyper IgM syndrome
- Ataxia telangiactasia
Bruton’s hypogammaglobulinemia
X linked recessive disorder
Bruton tyrosine kinase BTK gene affected (B cell areas)
B cell defect
Decreased IgG (defective opsonisation)
Increased risk of infections (esp pneumococci)
DiGeorge syndrome or velocardial facial defect
Causes and basic features
CATCH22
Deletion in long arm of chromosome 22 (del 22q 11) ➡️
Defect in TBX1 gene ➡️
Defective development of 3rd and 4th pharyngeal pouches ➡️
Thymic and parathyroid hyperplasia
Velocardial defect DiGeorge syndrome clinical features
C. Cleft lip and cleft palate A. Abnormal facies T. Thymic hyperplasia, T cell defect C. Cardiac abnormalities H. Hypocalcemia 22
Wiscott Aldrich syndrome
X linked recessive disorder Defect in WASP gene ➡️ Decreased IgM ➡️ 1. Eczema 2. Recurrent infections 3. Thrombocytopenia (size, number, function defect)
SCID (first disorder to be successfully treated by gene therapy)
Both T and B cell defect
ADA (adenosine deaminase) deficiency
Accumulation of substrates
Decreased level of IL-7, IL-15 cytokines ➡️:
1. NK cell proliferation (IL-15)
2. Decreased production/activation of T cells, B cells (IL-7)
Increased risk of Candida, pneumococci,…
Common variable immuno deficiency CVID
Commonly seen in children
Defect in BAFF (B cell activating factor) or ICOS (inducible costimulator) gene ➡️
B cell maturation defect ➡️
No immunoglobulin production (no plasma cell) ➡️
Increased risk of sinopulmonary infections, giardiasis, other auto-immune disorders (like rheumatoid arthritis) and malignancies
Isolated IgA deficiency
B cell can’t produce IgA
So IgG4 is also reduced
Increased risk of GIT, sinopulmonary, allergies, anaphylaxis and other auto immune disorders
Hyper IgE syndrome or the JOB syndrome
Autosomal dominant Defect in STAT3 gene Increased level of IgE Cold abscesses Course facial features
Hyper IgM syndrome
X linked recessive disorder Increased IgM Defective class switching ➡️ Decreased IgG, IgA, IgE ➡️ Recurrent infections like pneumocystis jeroveci IgM starts attacking blood elements ➡️ : 1. Autoimmune haemolytic anaemia 2. Autoimmune thrombocytopenia 3. Autoimmune leukopenia
Ataxia telangiactasia
ATM (DNA damage sensor) gene of chromosome 11 ➡️
Increased risk of neoplasms and immune defects are present
Amyloid definition
Pathological proteinaceous amorphous extracellular eosinophilic substance deposited in various tissues or organs in various conditions
Hyaline like pink substance
Misfolded protein
Structure of amyloid on electron microscopy
Non branching fibrils of indefinite length
7.5-10 nm in diameter
Structure of amyloid protein on X-ray crystallography or infrared spectroscopy
Cross beta pleated sheet structure which is responsible apple green birefringes of amyloid in Congo red under polarised light
Chemical nature of amyloid
95% fibrillar protein
5% P component
Classification of amyloidosis
- Localised:
DAMP - Systemic/ generalised
- Familial
Localised amyloidosis
- Type II DM (AIAPP-islet associated pancreatic peptide)
- Alzheimer’s disease (Aβ)
- Medullary carcinoma of thyroid (ACal)
- Prion disease (APr)
Generalised or systemic amyloidosis
- Primary amyloidosis:
Seen in light chain disorders (commonly λ) like multiple myeloma
AL - Secondary amyloidosis /reactive systemic amyloidosis:
- Chronic renal failure/ long term dialysis (Aβ2m-micro globulin)
- Senile/ ageing amyloidosis:
ATTR-normal transthyretin
Secondary amyloidosis /reactive systemic amyloidosis:
AA amyloid deposition Seen in A. Chronic inflammatory conditions: 1. Bronchiectasis 2. Rheumatoid arthritis (most common) 3. Tuberculosis (most common in India)
B. Chronic malignancies:
- Hodgkin’s lymphoma
- Renal cell carcinoma
Familial amyloidotic polyneuropathy
Autosomal dominant
Deposition of mutant transthyretin
ATTR
Familial Mediterranean fever
Example of familial amyloidosis
Autosomal recessive
AA
Pyrin protein deposition (pyrexia-fever)
Diagnosis of amyloidosis
Best and most commonly used test- Abdominal fat pad aspirate
Rectal biopsy
Then tongue biopsy
Stains for amyloid
- H and E: pink
- PAS-magenta (per-iodic shift reaction)
- Congo red-best stain:
On light-salmon pink
On polarised light-apple green birefringence - Methyl violet/ crystal violet- metachromatic stains
- Thioflavin S and T- inflorescence
Gross stain
Gross stain for amyloidosis
Cut surface with Lugol’s iodine- Mahogany brown ➡️ sulphuric acid is then added and if it then becomes blue
Then to confirm Congo red is used
Most common organ affected by amyloid
What are the effects
Kidney
It is also the most severely affected organ
Initially in the glomeruli
Usually affects the mesangium (can also affect the walls of capillaries and arterioles)
Clinically presents as nephrotic syndrome
Renal biopsy is done
Most common cause of death in primary amyloidosis
Heart disease
Most common cause of death in secondary amyloid
Renal disease
General gross features of amyloidosis
The organ is waxy
Firm in consistency
Usually organomegaly is present
Liver and amyloidosis
First affects Space of Disse (thin space between hepatocytes and sinusoids) ➡️ pressure atrophy of hepatic
Clinically presented as cirrhosis
Heart and amyloidosis
The subendocardium is the most commonly affected part Clinically: 1. Arrhythmia 2. Right bundle branch block 3. Restrictive cardiomyopathy
Amyloidosis and GIT
Macroglossia
Can affect many other parts of GIT
Spleen and amyloidosis
- Sago spleen
Splenic follicles are affected - Lardaceous spleen
Sinusoids are affected