Autoimmune Diseases Flashcards
HLA Associations
Type I Hypersensitivity Reaction
(Anaphylactic)
Systemic anaphylaxis
Local anaphylaxis
Type II Hypersensitivity Reaction
(Cytotoxic)
Complement-dependent reactions
Transfusion reactions
Erythroblastosis fetalis
Autoimmune hemolytic anemia
Pemphigus vulgaris
Some drug reactions
Goodpasture syndrome
Ab-dependent cell-mediated cytotoxicity
Ab-mediated cellular dysfunction
Myasthenia gravis
Grave disease (Ab against TSH receptor)
Type III Hypersensitivity Reaction
(Immune Complex Mediated)
- Antigens can be exogenous or endogenous
-
Systemic immune complex disease
- Form Ag-Ab complexes in circulation
- Deposit immune complexes in several tissues
- Inflammatory reaction in several tissues
-
Local immune complex disease (Arthus reaction)
- Tissue necrosis d/t acute immune complex vasculitis
Type IV Hypersensitivity Reaction
(Cell Mediated)
-
Delayed type hypersensitivity
- E.g. Granulomatous inflammation
- T-cell mediated cytotoxicity
Autoimmune Diseases
Local vs Systemic
Autoimmunity
Genetic Factors
- Familial clustering of autoimmune diseases
- SLE, autoimmune hemolytic anemia
- Linkage of autoimmune diseases w/ HLA antigens
- E.g. HLA B27
- Induction of autoimmune disease in transgenic mice
Microbial Agents
in
Autoimmunity
- Viral antigens and autoantigens may become ass. to form immunogenic units ⇒ bypass T-cell tolerance
- Microbial infections ⇒ tissue necrosis and inflammation ⇒ ↑ co-stimulatory molecules on resting APC’S in tissue ⇒ breakdown of T-cell anergy
- Inflammatory response ⇒ presentation of cryptic antigens ⇒ epitope spreading
- Superantigens and other microbial products (e.g. LPS) ⇒ ⊕ large pool of T and B-cells, some of which may be autoreactive
Autoimmune Injury
Pathogenesis
Autoimmune Diseases to Know
- Systemic lupus erythematosus
- Sjogren’s syndrome
- Systemic sclerosis (scleroderma)
- Inflammatory myopathies
- Dermatomyositis
- Polymyositis
- Inclusion body myositis
- Mixed connective tissue disease
Systemic Lupus Erythematosus (SLE)
Overview
- Chronic multi-systemic inflammatory autoimmune disease
- Remitting and relapsing in nature
- Characterized by production of a variety of auto-Ab
Systemic Lupus Erythematosus (SLE)
Epidemiology
- F:M ratio is 9:1
-
Ages 15 to 45 ⇒ child-bearing age
- Affects 1 in 700 women between ages 20-64
-
↑ incidence in African Americans, Hispanics, and Asians
- Incidence is particularly high in black women
Systemic Lupus Erythematosus (SLE)
Global Impact
- Survival improved over past 50 yrs to 90% at 10 years
- Better treatments for SLE and infections
- Many more mild cases are dx
- Non-fatal cumulative damage occurs in ~ 50% of survivors
- Most often in MSK system
- 25% with avascular necrosis and/or osteoporosis
SLE
Pathogenesis
- Strong genetic predisposition to disease
- 3-10x ↑ in clinical disease in MZ vs DZ twins
- Emphasis recently on defects in apoptosis
- Impaired removal of apoptotic cells ⇒ overload of Ag in circulating or target tissues
- Breakdown of immunologic self-tolerance
- Auto-antigens recognized as foreign ⇒ inflammatory response ⇒ activated complement, leukocytes, coagulation system, pro-inflammatory cytokines ⇒ local tissue damage
Systemic Lupus Erythematosus (SLE)
Immunologic Factors
-
Failure of self-tolerance in B-cells due to:
- Defective elimination of self-reactive B-cells in bone marrow
- Defects in peripheral tolerance
-
CD4+ helper T-cells specific for nucleosomal antigens
- Escape tolerance ⇒ contribute to production of high-affinity pathogenic auto-Ab
- TLR engagement by nuclear DNA and RNA contained in immune complexes ⇒ ⊕ B-cells
- Type I interferons ⇒ activated lymphocytes
- Other cytokines that may play a role including TNF family member BAFF
SLE
Clinical Heterogeneity
Hypothesis to Explain Clinical Heterogeneity of SLE:
- Environmental Etiologic Factor
-
Genetic Constitution Influences Immune Response
- HLA Antigens
- T-Cell Receptor Genes
- Immunoglobulin Genes
- Complement Component Genes
- Complement Regulatory Genes
- Cytokine Regulatory Genes
- Particular Auto-Ab Arise
- Particular set of auto-Ab present ⇒ clinical disease expression
Systemic Lupus Erythematosus (SLE)
Diagnosis
Old SLE diagnostic criteria:
Diagnosed using the criteria below
Need ≥ any 4 / 11 criteria present serially or simultaneously during any interval of observation
- Malar rash
- Discoid rash
- Photosensitivity
- Oral ulcers
- Arthritis of two or more peripheral joints w/ tenderness, swelling, or effusion
- Serositis ⇒ pleuritis or pericarditis
- Renal disorder ⇒ persistent proteinuria or cellular casts
- Neurologic disorder ⇒ seizures or psychosis in absence of offending drugs or known metabolic derangements
-
Hematologic disorder
- Hemolytic anemia w/ retiuculocytosis
- Leukopenia on two or more occasions
- Lymphopenia on two or more occasions
- Thrombocytopenia in absence of offending drugs
-
Immunologic disorder
- Anti-DNA Ab to native DNA in abnormal titer
- Anti-Sm ⇒ presence of Ab to Sm nuclear antigen
- Positive finding of antiphospholipid Ab based on:
- Abnormal serum level of IgG or IgM anticardiolipin Ab
- Positive test for lupus anticoagulant
- False positive serologic test for syphilis
- Known to be positive for at least 6 months
- Confirmed by a negative treponema pallidum immobilization or FTAA test
- Antinuclear Ab ⇒ abnormal titer in absence of drugs known to cause drug-induced Lupus syndrome
New SLE Diagnostic Criteria
Starts with presence of a positive ANA (or an equivalent test)
Includes points for many of the same criteria of old system
Uses a weighting system with different points for different sx
Anti-Nuclear Antigens (ANA)
Types
-
4 categories of ANA:
- Ab to DNA
- Ab to histones
- Ab to non-histone proteins bound to RNA
- Ab to nucleolar antigen
Anti-Nuclear Antigens (ANA)
Patterns
See 4 patterns w/ immunofluorescence:
Anti-Nuclear Ab (ANA)
Test
-
ANA test is sensitive but not specific
- 5-15% of normal individuals have ANAs
- Incidence ↑ w/ age
- Ab to double-stranded (ds) DNA and Smith Antigen are virtually diagnostic of SLE
- Smith Antigen ⇒ particles composed of RNA and protein
- High ds DNA Ab titer is often seen in pts w/ active renal disease
-
Lupus anticoagulant ⇒ actually is a pro-coagulant in vivo
- Blamed for miscarriages and ischemia
Systemic Lupus Erythematosus (SLE)
Genetic Factors
- ↑ incidence in families
- 20% of clinically unaffected relatives have auto-Ab
- 34% concordance in MZ twins
- If discordant, twin often has auto-Ab but is clinically ok
- This twin may lack environment needed for tissue injury
Systemic Lupus Erythematosus (SLE)
Non-Genetic Factors
-
Drugs ⇒ hydralazine, procainamide, d-penicillamine
- Get SLE-like response
- Ultraviolet light
- Viruses ⇒ no hard evidence
- Sex hormones
Systemic Lupus Erythematosus (SLE)
Mechanism of Tissue Injury
- Most visceral lesions mediated by immune complexes
- Type III deposit ⇒ e.g. DNA-antiDNA deposits in glomeruli
- Auto-Ab against RBC, WBC, platelets ⇒ opsonization ⇒ phagocytosis
-
Antiphospholipid Ab syndrome ⇒ venous and arterial thromboses
- Can see spontaneous miscarriages, etc.
Morphology Of SLE
-
Characteristic lesions result from deposition of immune complexes
- Found in the blood vessels, kidneys, connective tissues, and skin
-
Acute necrotizing vasculitis
- Involves small arteries and arterioles
- May be present in any tissue
- Fibrinoid deposits in vessel walls
- Chronic stage ⇒ vessels undergo fibrous thickening w/ luminal narrowing
SLE
“Typical” Clinical Presentation
Young woman < 40 y/o:
- Arthritis or arthralgia ⇒ 55%
- Skin involvement/Malar rash ⇒ 20%
- Nephritis/Proteinuria ⇒ 10%
- Fever/Fatigue/Malaise/Wt Loss ⇒ 15%
- Other ⇒ 10%
- Most pts have sx in only 1-2 systems at onset
- Nany accumulate organ-system involvement over several years
Systemic Lupus Erythematosus (SLE)
Clinical Manifestations
Renal Lupus
- Up to 50% of SLE have clinically significant renal involvement
-
Manifestations may include:
- Persistent proteinuria > 500 mg/24 hr or > 3+
- Cellular casts (red cell, granular, tubular or mixed)
- Nephrotic syndrome
- End-Stage Renal Disease
- Best studied SLE organ involvement
- Excellent clinic-pathological correlates in SLE
- Kidney biopsy eval. w/ LM, EM, and IF
SLE
Class I ‐ Minimal Mesangial Lupus Nephritis
- Least common type
- Can appear normal on LM
- Granular mesangial deposits of Ig and complement on EM and IF
SLE
Class II ‐ Mesangial Proliferative Lupus Nephritis
- Seen in 5-10% of biopsies in SLE
- Clinical ⇒ microscopic hematuria and proteinuria
- Histology:
- Moderate ↑ in mesangial matrix and # of mesangial cells
- Granular mesangial deposits of Ig and complement on EM and IF