Final week Flashcards
Define Self-antigens:
An individual own antigens (blood type antigens)
Define immunologic tolerance:
Unresponsiveness to self-antigens (negative selection process)
Define tolerogens:
Antigens that induce tolerance
Define Immunogens:
Antigens that induce an immune response
Define Autoimmunity:
Failure of self-tolerance and resulting immune reaction to self-antigens
What is central tolerance?
- Immature developing lymphocytes encountering self-antigens in generative lypmhoid organs
- T cells: deletion and regulatory T cells
- B cells: receptor editing, deletion, anergy
What is peripheral tolerance?
- Mature lymphocytes encounter self-antigens in secondary lymphoid organs
- T cells: anergy, suppression, deletion
- B cells: anergy, suppression, deletion
What are the 2 main pathways for central tolerance in T cells?
- Negative selection (deletion)
- Development of regulatory T cells
- The tolerance of T cells usually influences B cell tolerance
Where do DN thymocytes enter the thymus?
Right at the border of the medulla, where they then venture into the cortex for maturation
What is AIRE?
- AutoImmune Regulator Protein (AIRE)
- Expressed in thymic medullary epithelial cells
- Presents peripheral tissue antigens to thymus
- Without AIRE, there is no regulation and autoimmunity results!
What is APECED and its classic triad?
- Autoimmune PolyEndocrinopathy Candidiasis Ectodermal Dystrophy
- Classic Triad: mucocutaneous candidiasis, adrenal insufficiency, and hypoparathyroidism
What is the mode of inheritance for APECED?
- Autosomal recessive
- Mutations in AIRE gene
Which T cells do not depend on AIRE for their development?
Regulatory T cells
Where is icos expressed and what is its function?
- Expressed on activated T cells
- Costimulation of T cells & generation of T follicular helper cells
Where is CTLA-4 expressed and what is its function?
- Activated T cells
- Negative regulation of immune response & self-tolerance
Where is PD-1 expressed and what is its function?
- T cells, B cell, and myeloid cells (activated)
- Negative regulation of effector T cells & self tolerance
What are the two forms of T cell anergy?
After recognition of self-antigen
- Signaling block
- OR
- Engagement of inhibitory receptors
What is CD25?
Alpha chain for IL2 receptor
What is the difference between natural and induced T regs?
- Natural develop in the thymus
- Induced develop in the peripheral tissues (TGF-beta)
What are the 3 main ways T regs suppress the immune response?
- Production of inhibitory cytokines (IL-10 & TGF-beta)
- Expression of CTLA-4
- Expression of IL-2 receptor and capture of IL-2
What is IPEX and its classic triad?
- Immune Dysregulation, Polendocrinopathy, Enteropathy, X-linked Syndrome
- Classic Triad: enteropathy (diarrhea), dermatitis (eczema), endocrine disease (diabetes/thyroid)
What is the difference between intrinsic and extrinsic in peripheral T lymphocyte deletion?
- Intrinsic- cell death caused by deficiency of survival genes (mitochondria releases inducers of apoptosis)
- Extrinsic- cell death caused by engagement of death receptors (FasL and Fas interaction)
What is ALPS and its common mutations?
- Autoimmune Lympho-Proliferation Syndrome
- Disorder of apoptosis
- Dominant mutation: Fas, FasL, caspase 8, caspase 10
Which antigens are nonprotein and T-independent?
- Polysaccharides
- Lipids
- Nucleic Acids
What immunoglobulin isotype responds to T-independent antigens?
IgM (short-lived plasma cells)
What are the pathways for central B cell tolerance?
- If self-reactive, can form new light chain to avoid
- If self-reactivity continues, apoptosis
- If responds to self-antigen with low-avidity, it can enter anergy
What are the two main forms of peripheral B cell tolerance?
- Anergy and deletion (in absence of T cell co-stimulation)
- Regulation by inhibitory receptors
What are the common steps in autoimmunity development?
- Inheritance of susceptibility gene and failure of self-tolerance
- Tissue injury and inflammation
- Activation of tissue APCs and self-reactive lymphocytes
- Self-reactive effector lymphocytes cause tissue injury
What are some common polymorphisms (Non-HLA) and their associated autoimmune disease?
- PTPN22 (RA and others)
- NOD2 (Crohn’s Disease)
- CD25 (MS, Type 1 diabetes, others)
- C2, C4 (SLE)
- FCGRIIB (SLE)
What are some single-gene defects that cause autoimmunity?
- AIRE (APECED)
- Foxp3 (IPEX)
- FAS (ALPS)
What are the 2 main form of environmental factors that lead to autoimmunity?
- Induction of costimulators on APCs
- Molecular mimicry
In what disease are both B lymphocyte and T lymphocyte tolerance defective?
Systemic Lupus Erythematosus
What are some common environemntal factors associated with SLE?
- UV radiation
- Viral infection
- Drugs and chemicals
What are some common Anti-__ antibodies involved in SLE?
- Antinuclear antibody
- Anti-dsDNA antibody
- Anti-Smith antibody
- Anti-Ro (SSA) antibody
- Anti-La (SSB) antibody
- Anti-RNP antibody
- Anti-histone antibody
A malar rash is associated with what disease?
Lupus
What hormonal factors are associated with SLE?
- Increased in women during child bearing years
- Estrogen-induced flares
Define hypersensitivity
Overreaction of normally protective response that results in tissue injury and disease
What are the 3 common triggers of hypersensitivity?
- “self” antigens- autoimmunity
- Microbial antigens- excessive inflammation
- Environmental antigens- allergy/atopy
What is the most common type of hypersensitivity?
Type 1
How is type 1 hypersensitivity characterized?
- Allergy or atopy
- Rapid onset (minutes)
- Antigen-specific IgE
- Mast cell (histamine) and eosinophil involvement
- Vasoactive mediators, lipid mediators, cytokines
What are some common examples of Type 1 hypersensitivity?
- Allergic rhinitis
- Atopic asthma
- Anaphylaxis
What antibodies mediate type 2 and 3 hypersensitivity?
IgG and IgM
Which type(s) of hypersensitivity often involve auto-antibodies or foreign antigens?
Type 2 and 3
What is the role of the antibodies in type 2 hypersensitivity?
- Antibody directly binds the target
- Antigens are specific cells or extracellular matrix
- Local, tissue specific
What is the role of the antibodies in type 3 hypersensitivity?
- Immune complex deposition
- Antigens present in circulation
- Systemic
Which class of immunoglobulins has the most subtypes?
- IgG (1-4)
- IgA has 2 subtypes
How is type 2 hypersensitivity characterized?
- Cytotoxic hypersensitivity
- Onset in minutes-hours
- Complement and Fc receptor mediated (involves opsonization/phagocytosis or hormone signaling)
- Neutrophils can cause direct tissue injury
What are some examples of Type 2 hypersensitivity?
- Goodpasture’s Syndrome
- Idopathic thrombocytopenic purpura (ITP)
- Autoimmune hemolytic anemia (AIHA)
- Grave’s (antibody stimulates TSH receptor)
- Myasthenia gravis (antibody inhibits Ach receptor)
In what disease are antibodies against the basement membrane of the kidney and lung made?
Goodpasture’s syndrome (type 2)
How is type 3 hypersensitivity characterized?
- Immune complex hypersensitivity
- Onset within hours
- Complement and Fc receptor mediated
- Complexes deposited in vascular basement membrane
- Lysosomal enzymes and ROS cause damage, neutrophils (vasculitis)