Immune Mechanisms of Diabetes Lecture (Dr. Shnyra) Flashcards
1
Q
Diabetes and Insulin
A
- Diabetes was considered a TERMINAL CONDITION before Insulin was available for therapy
- History created on January 11, 1922 when a 14 year old boy with T1D become the FIRST RECIPIENT OF INSULIN
- Fredrick Grant Banting received the Nobel Prize for Insulin at the age of 32
2
Q
Classification of Diabetes
A
Diabetes Mellitus Type I A: 1) Immune Mediated 2) Immune Etiology Distinction 3) Results in Insulin Dependence, with a loss of Beta Cells
Type I B:
1) Idiopathic
2) Unknown Etiologic Distinction
3) Results in Insulin dependent, with loss of Beta Cells
Type II:
1) Insulin Resistance and relative Insulin Deficiency is the Etiologic Distinction
2) Oral Hypoglycemic agents are Effective EARLY in Life
3
Q
Genetics, Behavioral Factors, and Environment Triggers have impact on the development of T2D
A
- Genetic susceptibility, sedentary lifestyle, high-fat diet, and psychological stress have Complementary effects on the Development of T2D
4
Q
Changes in Immune Cell Populations in Adipose Tissue
A
- LEAN Adipose Tissue contains GREATER portion of M2/M1 Macrophages
- It also contains a Large Number of REGULATORY T CELLS (Treg Cells)
- OBESITY Leads to Adipocyte NECROSIS and an INCREASE in M1 Macrophages
- There is also a REDUCTION in TREG CELLS and an INCREASE in B CELLS, CD4+ Th1 Cells, and CD8+ T Cells
5
Q
Obesity results in INFLAMMATION of ADIPOSE TISSUE
A
- Lean Adipose tissue has ELEVATION Fractions of ANTI-INFLAMMATORY M2-like Macrophages and Treg Cells
- The Local Environment is DOMINATED by ANTI-INFLAMMATORY CYTOKINES IL-10, IL-4, IL-13
- Long term NUTRIENT EXCESS leads to APOPTOTIC and NECROTIC DEATH of Adipocytes
- Upon Obesity, the ADIPOSE Tissue has a Mixed M1/ M2 Phenotype of ATMs, more Cd8+ T Cells than CD4+ Th1 Cells, and fewer Treg Cells
- The Immune Cells promote CHRONIC INFLAMMATION through the production of Pro-Inflammatory Cytokine and Chemokines such as IL-1, TNF-Alpha, IL-6, CCL2, CCL3, and CXCL8 (IL-8)
6
Q
What is Type I Diabetes
A
- T1D is characterized by IMMUNE-MEDIATED Destruction of PANCREATIC Beta Cells resulting in INSULIN DEFICIENCY
- Patentis with T1D are prone to KETOACIDOSIS, a Dangerously HIGH levels of Ketones in the Blood
- Most cases are Characterized by AUTOANTIBODY markers of Beta Cells DESTRUCTION and Strong HLA ASSOCIATIONS
- Type I Diabetes is a T CELL MEDIATED AUTOIMMUNE DISORDER
- The onset of T1D is associated with INFILTRATION of the ISET of LANGERHANS by MONONUCLEAR CELLS and CD8+ T Cells. This infiltrate is termed INSULITIS!!!!!!!!
7
Q
Which Factors Contribute to T1D?
A
- T1D is the SECOND MOST FREQUENT Autoimmune Disease in Childhood
- The LONG-TERM Micro and Macro-Vascular complication son Diabetes are associated with he leading causes of Disability and even Morality in Young Adults
- T1D Development involved Genetic and Environment Factors, such as BIRTH Delivery Mode, use of Antibiotics, and Diet
- Gut MICROBIOTA could be the Link between Environmental Factors, the Development of AUTOIMMUNITY, and T1D
8
Q
Environment Factors of T1D
A
- The CONCORDANCE RATE for T1D is MONOZYGOTIC TWINS is not 100% but about 30 to 50%, SUGGESTING ADDITIONAL NON-GENETIC INFLUENCES!!!
- T1D INCIDENCE is INCREASING about 3% per year, the Rate too HIGH to be attributable to Changes in Susceptibility Genes
- Evidence linking the Environment and T1D in humans in INDIRECT (EPIDEMIOLOGICAL and ANIMAL STUDIES)
- There is also a 350 fold VARIATION in the INCIDENCE of T1D in different countries Worldwide
9
Q
Breast Feeding vs Cow Milk
A
- A variety of studies have shown AN INVERSE CORRELATION BETWEEN A DECREASE IN BREAST- FEEDING and the INCREASE IN TYPE1 DIABETES RISK
- EARLY EXPOSE to Cow Milk in life (Ex: because of lack of Breast Feedgin) may CONTRIBUTE to T1D:
a) IMMUNE TOLERANCE TO INSULIN might also be compromised by early exposer to Cow Milk which CONTAINS MUCH LESS INSULIN than does Human Milk - However, there is INCONSISTENCY in results of those studies which may attribute to:
1) VARIATIONS in COMPOSITION of Milk
2) GEENTIC VARIATION in Cow Proteins
3) Vitiations in MILK-SENSITIVE DIABETES-PRONE INDIVIDUALS in Studies
10
Q
Diet Factors
A
- WHEAT GLUTEN is a POTENT DIABETOGEN
- The risk of T1D is HIGHER in patients with GLUTEN SENSITIVE ENTEROPATHY
- Other Environmental factors linked with T1D include VITAMIN D, an Immune Modulator and Suppressant
a) The NORTH-SOUTH Gradient of T1D incidence in Europe, with Lower Mean SUNSHINE HOURS in the North - PSYCHOLOGICAL STRESS has also been suggested as a Trigger for Diabetes, but data are sparse and Inconsistent
11
Q
Hygiene Hypothesis and T1D
A
- Exposure to a variety of Infectious Agents during early Childhood might be PROTECTIVE in T1D as well
- A Constant INCREASE in the Incidence of T1D contrasted by a GRADUAL DECREASE in the Incidence of INFECTIOUS DISEASES such as TB, Mumps, Measles, Hepatitis A, and Enterovirus Infections
- A Variety of studies have shown an INVERSE CORRELATION between a Decrease in Breast-Feeding and the INCREASE in T1D Risk.
12
Q
Role Infections in T1D
A
- STREPTOZOCIN and BIFILOMYCIN A1 form Streptomycin are CYTOTOXIC FOR BETA CELLS
- BACTERIA may also act as ADJUVANTS for the Immune Response to food Ags
- VIRUSES may act against Beta Cells by a Mechanisms that include:
a) Direct CYTOTOXICITY
b) Triggering of an Autoimmunity by MOLECULAR MIMICRY - Viruses which have been Implicated with T1D:
a) MUMPS
b) RUBELLA
c) Cytomegalovirus
d) Enteroviruses
e) Retroviruses
13
Q
Genetics of T1D
A
- Familial CLUSTERING in T1D
- The RISK of developing T1D before age 20 years:
a) 6% int he Sibling of an Affected Patient
b) 0.4% in General Population
- The CONCORDANCE:
a) 30 to 50% in Monozygotic Twins
b) 10% in Dizygotic Twins
14
Q
What genes determine T1D Susceptibility
A
- Type 1 Diabetes is a MULTIFACTORIAL AUTOIMMUNE Disease
- T1D patient with ant their relatives are at INCREASED RISK for OTHER AUTOIMMUNE DISEASE (Thyroid Autoimmunity and Addison’s Disease
- There may be NO SPECIFIC DIABETES GENE, but….
- Only specific “WRONG” COMBINATIONS of Normal POLYMORPHISMS!!!!
15
Q
What genes are Associated with T1D?
A
- About 18 GENES of varying potency are associated with Susceptibility to T1D
MOST SIGNIFICANT
1) The HLA Region (the MHC Gene on CHROMOSOME 6): Presentation of INSULIN Ags for CD8+ T Cells
2) The INSULIN GENE (CHROMOSOME 11): Ag for Autoimmune Response
3) REGULATORS of Insulin Gene expression in the Thymus (AIRE)
4) The CTLA-4 GENE (CHROMOSOME 2): Regulation of Autoimmune REsponse
16
Q
Role of HLA in T1D
A
- HLA Alleles DQ2/ DQ8 and DR3/ DR4 are the HIGH-RISK Alleles
- Alleles DQ2/ DQ8 (Haplotypes with DR3DQ2 or DR4DQ8) found in more than 90% OF INDIVIDUALS with T1D!!!!!!!!!
- Heterozygous Genotypes DR3/ Dr4 are most COMMON IN CHILDREN diagnosed with T1D prior to the age of 5 (50%)
- HLA Class II molecules that LACK ASP57 OF THE BETA CHAIN are often found among individuals with T1D
- HAL Class II Haplotypes such as DR2/ DQ6 confer dominant PROTECTION
17
Q
The Insulin Gene (IDDM2)*****
Check Lecture
A
- Mapped to a Region contains the VARIABLE NUMBER OF TANDEM REPEATS (VNTR) in the PROMOTER REGION of the Insulin Gene
- the VTNR POLYMORPHISM is categorized into Class I, II, and II
- The SUSCEPTIBLE CLASS I Alleles of the Insulin VNTR are associate with LOWE INSULIN mRNA SYNTEHSIS resulting in:
a) Low Ag (Insulin) Synthesis
b) Low Ag Presentation in the Thymus
c) Failure of Deleting Self-Reactive CD8 T Cells
- The CENTRAL TOLERANCE is BROKEN with Class I Alleles
18
Q
Transcription AutoImmune Regulator (AIRE)
A
- Transcriptional EXPRESSION of INSULIN in the Thymus is controlled by AIRE
- Malfunctioning of AIRE results in LOWER LEVELS OF INSULIN mRNA in the Thymus
- The Absence of Insulin results in FAILURE OF DELETING Insulin-Reactive T Cells and the CENTRAL TOLERANCE is Broken!!!!!!
- AIRE is a CRITICAL Factor in the Induction of Central Tolerance against Insulin
19
Q
CTLA -4 Gene (IDDM12)
A
- CTLA4 (Cytotoxic T Lymphocyte Antigen-4) is the SUSCEPTIBILITY LOCUS on Chromosome 2 to be associated with T1D
- CTLA-4 (CD152) encodes a Glycoprotein that is a CD28 HOMOLOGUE and bind B7 PROTEIN (CD80/ 86)
- CTLA-4 may COUNTER-REGULATE the CD28- Dependent TCR ACTIVATION of T CELLS
- The Function of CTLA-4 is SUPPRESSION of T CELL ACTIVATION and activation of its APOPTOSIS
20
Q
Mechanisms of Action of CTLA-4
A
- Engagement of CTLA-4 on a T Cell may deliver INHIBITORY SIGNALS that Terminate further activation of that cell (Cell-Intrinsic Function of CTLA-4)
- CTLA-4 on Regulatory or responding T Cells binds to B7 Molecules on APCs or removes these molecules form the surface of APCs, making the B7 costimulators unavailable to CD28 and Blocking T Cell Activation
21
Q
CTLA-4 Controls the PERIPHERAL TOLERANCE
A
- CTLA-4 competes with CD28 for binding CD80 leading to Cell-Cycle arrest that prevents Expansion of activated T Cells
- Failure of T Cells to express the CTLA-4 gene due to Mutation may Contribute to ABERRANT IMMUNE RESPONSES seen in T1D
- Soluble Recombinant CTLA4 (sCTLA4) has been used in Clinical Trials or TREATMENT of AUTOIMMUNE DISEASES
22
Q
CTLA-4 on the Board Exams
A
IN ACTIVATED T CELLS CD152 (CTLA4):
a) Biomes Sequestered within GOLGI
b) Binds to Appropriate MHC
c) Induces PROGRESSION through the Cell Cycle
d) Stimulate Transcription of IL-2 mRNA
e) BEGINS TO MOVE TO THE MEMBRANE AND BINDS CD80/CD86!!!!! (THIS IS THE ANSWER TO THE QUESTION!!)
23
Q
Autoantibodies in T1D
A
- ISLE CELL AUTOANTIBODIES (ICA) are detected in Individuals with T1D are present with INCREASED FREQUENCY among individuals recently diagnosed with T1D
- Autoantibody production APPEARS IN ADVANCE (Months to years) of the Metabolic Changes T1D can be used to predict Disease
- Their present CONFIRMS a DIAGNOSIS of Type IA Diabetes
- THE SPECIFICITIES of Several Identified ICA include:
1) Glutamic Acid Decarboxylase (GAD65)
2) Insulinoma Antigen-2 (IA-2, TYROSINE PHOSPHATASE)
3) Insulin AutoAntibodies (IAA)
24
Q
Pathogenic Role of Auto-Abs
A
- Despite the utility of Autoantiboes for Diagnostic Purposes, their PATHOGEN CONTRIBUTION IS CONTROVERSIAL:
a) T1D cannot be transferred using Serum from Diabetic Humans —-> PLASMAPHERESIS PRIVETS LITTLE THERAPEUTIC BENEFIT
b) T1D was reported in a 14 year old male with X LINKED AGAMMAGLOBULINEMIA
WHAT IS THE PATHOGEN ROLE?
- Autoantibodies MAY AFFECT THE TIME COURSE of Disease Development
25
Autoantibodies
- The presence of 2 OR MORE distinct Antibody specificities is HIGHLY PREDICTIVE of future T1D (Five year risk = 28- 66%)
- When COMBINED WITH HLA typing, Autoantibody Screening is also USEFUL FOR PREDICTION disease in General Populations
26
T1D
- T1D is Th1-MEDIATED DISEASE!!!!
27
Th1/ Th2 Paradigm
- The T1D AUTOREACTIVE T CELLS belong to the Th2 SUBSET
28
Pathogenic Role of T Cells
- T Cells are ACTIVATED IN THE LYMPH NODES that drain the Pancreas
- Once activated, ISLET Specific T Cells TRAFFIC TO THE PANCREAS where they PROLIFERATE and accumulate resulting in Organ Specific INFLAMMATION
- LOCAL APCs capable of presenting Ag in the Context of CLASS II MHC molecules and Secreting IL-12 play an important role in the Pathogenesis if T1D
- These PACs activate Ag-specific CD4 T CELLS and further stimulated IFN-GAMMA
- IFN-Gamam INHIBITS Th2 CYTOKINE PRODUCTION (IL-4, IL-5, IL-10) and enhance IL-1Beta, TNF-Alpha, and free radical production of Macrophages which are all toxic to Islet Beta Cells
29
Cell-Mediated Immunity and T1D
- A counter regulatory role of Th1/ Th2 subsets would suggest that T1D WOULD NOT OCCUR WITH ASTHMA
- However, ASTHMA IS MORE PREVALENT in Children with T1D than Non-Diabetes Children
- What is the COMMON DENOMINATOR?: The Failure of Regulatory Mechanisms controlled by TREG CELLS
- SUSCEPTIBILITY to T1D may be greatly enhanced when TREG CELLS FAIL TO PREVENT ACTIVATION/ Expansion of Auto-Reactive T Cells
- Islet Specific Pathogenic Clones of T Cells are found in Healthy Individuals, but T1D i prevented and the PERIPHERAL SELF TOLERANCE is maintained by Treg Cells
30
T Regulatory Cells
- Treg cells can ACT locally IN TISSUES and draining LYMPH NODES
- Treg cells become ACTIVATED BY LOCAL APC presenting Auto-Ag
- Treg cells SUPPRESS APCs DIRECTLY through Cell- Cell interactions or INDIRECTLY (Cytokines or Chemokines)
- Alternatively, Treg Cells might act directly on T CELL EFFECTORS
31
Mechanisms of Action of Regulatory T Cells
- Regulatory T Cells appear to suppress Immune Responses at MULTIPLE STEPS. They may also directly suppress B CELL ACTIVATION and Inhibit the Proliferation and Differentiation of NK Cells.
- Although SEVERAL MECHANISMS of Suppression have been proposed, the following are the best supported by available data:
1) PRODUCTION of the IMMUNOSUPPRESSIVE Cytokine IL-10 and TGF-Beta
2) REDUCED ABILITY of APCs to STIMULATE T CELLS. One proposed Mechanisms of this action is Dependent ob Binding of CTLA-4 on Regulatory Cells to B7 Molecules on APCs
3) CONSUMPTION of IL-2 because of the HIGH Levels of Expression of the IL-2 Receptor, these cells may absorb IL-2 and deprive other T Cell populations of tis Growth Factor, resulting in Reduced Proliferation and Differentiation of other IL-2 Dependent Cells
32
Cd4+/ Cd25+ Treg Cells in T1D
- ISLET Specific Ags are released and presented in PANCREATIC LYMPH NODES
- The Ags can activate damaging CD4+ and CD8+ T CELLS
- The Ags can also activate CD4+/ CD25+ T reg Cells
- Treg Cells PREVENT ACTIVATION of both CD4+ and CD8+ T Cells
- Treg Cells are shown to PREVENT DIABETES in NOD Mice (Non-Obese Diabetic)
33
Key Concepts
- REGULATORY T CELLS ARE IMPORTANT
- The Loss of Treg in IPEC Syndrome leads to NEONATAL DIABETES:
1) IMMUNODYSREGUALTION, POLYENDOCRINOPATHY, ENTEROPATHY, X-Linked SYNDROME, a rare disease linked to the Dysfunction of the TRANSCRIPTIONAL ACTIVATOR FOXP3
2) FoxP3 (Forehead box P3) is a SPECIFIC MARKERY of Natural T REGULATORY CELLS
- FOXP3 appears to Function as the MASTER REGULATOR in the DEVELOPMENT and FUNCTION of Regulatory T Cells
34
Key Remaining Questions in T1D
BASIC SCIENCE:
- What genes determine Type 1A Diabetes SUSCEPTIBILITY?
- What triggers or Suppresses the activation of Autoimmunity?
- What are the MAJOR TARGET Molecules and is there a primary Auto-Ag?
- What are the EFFECTOR MECHANISMS for Islet Destruction?
CLINICAL
- Is Type 1A Diabetes PREDICTABLE?
- Is the rate of PROGRESSION to over Diabetes Predictable?
- Is Type 1A Diabetes PREVENTABLE?
35
Three Major Islet Auto-Ags in T1D
1) INSULIN/ PROINSULIN:
a) Tissue Distribution:
- Beta Cells, Islet of Langerhans
b) Function:
- Regulator of Blood Glucose
c) PREVALENCE of AUTOANTIBODIES at DIAGNOSIS
- 50 to 70%
d) Comments:
- Most PREVALENT in Children with Type 1 DM
2) GLUTAMIC ACID DECARBOXYLASE -65 (GAD65)
a) Tissue Distribution:
- Endocrine Cells in Islets of Langerhan
- Central and Peripheral Nervous System
b) Function:
- GABA Synthesis
c) PREVALENCE of AUTOANTIBODIES at DIAGNOSIS
- 60 to 80%
d) Comments:
- Most prevalent in ADULT-Onset Type 1 DM
3) ISLET PROTIEN TYROSINE PHOSPHATASE (PTPs) IA-2 and IA-2Beta (Phogrin)
a) Tissue Distribution:
- Endocrine Cells in Islets of Langerhans
- Central and Peripheral Nervous System
b) Function:
- Unknown
c) PREVALENCE of AUTOANTIBODIES at DIAGNOSIS
- 40 to 60%
d) Comments:
- None
