CLS 306: Lecture 7 - Autoimmunity, Autoimmune Diseases

Self-antigens

Autoimmune disorders are immune responses are targeted toward (——) and result in damage to organs and tissues in the body

• T mediated

• Abs to host Ag

Autoimmune diseases are mediated by either (——) or (——)

Self tolerance

Ability of the immune system to discriminate “self” from “non-self” or “foreign”, unresponsiveness to self Ag

• If TCR reacts with self Ag → Th removed

• Some self reactive Th → circulation → Treg

• If BCR reacts with self Ag → B removed

• Some self reactive B released → modify BCR

• BCR weak reaction → anergy

Describe the development of central self-tolerance (5)

Anergy

Occurs if BCR reacts weakly with self antigens during the development of self tolerance

• Self reactive T cells removed (apoptosis, Treg inhibition, lose co-stimulatory signal from APC, or bind to CTLA-4)

• Self reactive B removed (apoptosis, become anergic, inactivated by CD22 receptor)

How does peripheral self tolerance develop in T cells (4) and B cells (3)

• Genetics

• Exposure to environmental factors

• Defects in immune regulation

The development of autoimmune diseases is thought to be caused by complex interactions between… (3)

HLA-B27

People inheriting (——) allele are at 100x higher risk of developing ankylosing spondylitis

• IL2RA

• CTLA4

The (——) gene is involved in T cell activation and maintenance of Treg; the (——) gene has an inhibitory effect on T cell activation

20-30 genes

Most autoimmune diseases require around (——) genes to manifest

Genetics

Factor that plays an important role in developing autoimmune diseases; explains why these diseases are more prevalent among family members and more in monozygotic twins than dizygotic

Hormones

Factor that plays an important role in developing autoimmune diseases; explains why women are higher risk of developing these diseases than men

Tissue damage

Exposure of cryptic antigens due to (——) → autoimmune disease; Ab against lens after ocular injury, Ab against sperm after vasectomy, Ab against DNA after overexposure to UV radiation

Molecular mimicry

Main mechanism of developing autoimmune diseases after microbial infection; bacterial or viral agents contain antigens that closely resemble the structure or amino acid sequence of self-antigens; exposure to such foreign antigens may trigger immune response that cross-reacts with similar self-antigens

Streptococcus pyogenes M protein and N-acetyl glucosamine → human myosin → rheumatic fever

Example of molecular mimicry leading to autoimmune infection

Genetic and environmental factors

Although the precise etiology of autoimmunity is unknown, there is much evidence that suggests that this heterogeneous disease entity is caused by complex interactions between…

Females (9:1)

Which population is more likely to develop SLE

• dsDNA

• Histones

• lymphs, erythrocytes, PLTs

• phospholipids

• ribosomal components

• endothelium

SLE patients typically have several circulating autoantibodies. What are the different targets of these autoantibodies (6)

• Complement

• Glomerular basement membrane

In SLE, anti-dsDNA complexed with (——) circulate and deposit on (——) of the kidneys → joint, skin, and renal involvement

Lupus anticoagulant

Lupus autoantibodies against phospholipids target components of the normal blood clotting process, leading to the increased risk of forming clots (?)

• CBC: leukopenia, thrombocytopenia, anemia

• ESR: high

• CRP: low or normal

• ANA: positive

• Antibodies: dsDNA and Sm nuclear antigen

Lab diagnosis of SLE (CBC, ESR, CRP, ANA, antibodies)

• Antigen: dsDNA

• IF pattern: Homogeneous

• Disease association: SLE

anti-dsDNA antigen, IF pattern, and disease association

• Antigen: Extractable nuclear antigen (U-rich RNA component)

• IF pattern: Coarse speckled

• Disease association: Diagnostic SLE

Anti-Sm antigen, IF pattern, disease association

Fluorescent anti-nuclear antibody (FANA)

(IIF) (——) testing has been the most widely used and accepted test because it is highly sensitive, detects a wide range of antibodies, and is inexpensive and easy to perform.

• Commercial slide fixed with HEp2 cell line

• Incubate with patient serum (serial dilution start 1:80 or 1:160) → ANA binds to HEp2 nucleus

• Wash (remove unbound Ab)

• Add fluorescent labeled anti-human Ig → incubate

• Wash

• Cover slip, mount, view at 400x

  • Titer above 160 are significant

Describe the process of testing for FANA through IIP (6)

Homogeneous

(ANA fluorescent pattern) This pattern is characterized by uniform straining of the entire nucleus in interphase (nondividing) cells and of the condensed chromosomal region in metaphase cells. It is associated with antibodies to dsDNA, histones, and nucleosomes (nonspecific). The pattern is found in patients with SLE, drug-induced lupus, chronic autoimmune hepatitis (AIH), and huvenile idiopathic arthritis

Speckled

(ANA fluorescent pattern) These patterns are characterized by discrete, fluorescent specks throughout the nuclei of interphase cells. The speckled group is divided into three subgroups depending on whether the pattern is dense fine, tiny/fine, or large/coarse. The fine and coarse patterns are associated to ENAs, and can be found in patients with SLE, Sjogren’s syndrome, systemic sclerosis (SSc), and other SARDs

Nucleolar

(ANA fluorescent pattern) Prominent staining of the nucleoli within the nuclei of interphase cells is seen in this pattern. The size, shape, and number of the nucleoli per cell are variable, and staining can be smooth, clumpy, or speckled, depending on the type of antibody present. Staining may or may not be present in the dividing cells. The nucleolar patterns are primarily caused by antibodies to RNA and RNP and are seen mainly in patients with SSc but can also be present in patients with other SARDs

• HLA-DRB1 alleles

• PTPN22 gene polymorphisms

Rheumatoid arthritis has the strongest associations with the (—2—) genetic regions.

• Rheumatoid factor (RF)

• Ab for cyclic citrullinated peptides (CCP)

Patients with rheumatoid arthritis are positive for… (2)

altered DNA methylation affecting transcription of critical genes

Epigenetic factors, such as (——) are also believed to play a role in the pathogenesis RA

Cigarette smoking

The strongest environmental risk factor for RA is believed to be (——), which doubles the risk of developing the disease

bone and cartilage in the joints

Rheumatoid arthritis is caused by an inflammatory process that results in the destruction of…

• B/T lymphs

• Plasma cells

• Dendritic cells

• Mast cells

• Granulocytes

Infiltration of the inflamed synovium with (—5—) is evidence of immunologic activity within the joint

• IL-1

• IL-6

• IL-17

• TNF-⍺

(Rheumatoid arthritis) the balance between proinflammatory and anti-inflammatory cytokines in RA appears to be tipped toward continual inflammation with the cytokines… (4)

Matrix metalloproteinases

The cytokines associated with rheumatoid arthritis trigger a release of (——) from fibroblasts and macrophages; these enzymes degrade important structural proteins in the cartilage

Osteoclasts

Bone lesions are a characteristic of rheumatoid arthritis due to the hyperactivation of…

TNF-⍺ and RANKL (receptor activator of nuclear factor kappa-B ligand)

In rheumatoid arthritis, (—2—) inhibit osteoblast differentiation and bone formation while also activating osteoclasts

Rheumatoid factor

(Rheumatoid arthritis key antibody) an IgM against FC portion of IgG, enhances activity of macrophages and Ab presentation to APCs

Anti-cyclic citrullinated peptide antibody (anti-CCP or ACPA)

(Rheumatoid arthritis key antibody) Respond to citrullinated proteins released from dead granulocytes or macrophages

HLA-DRB1

Overexpression of citrullinated proteins may provoke an immune response in individuals with certain (——) alleles

• Positive in 70-90% or arthritis patients

• Negative result does not exclude RA

• Positive result is not specific to RA (5% in healthy, 10-25% over 65)

The initial test for rheumatoid arthritis is RF. What are its characteristics (3)

• SLE

• Sjogren’s syndrome

• Scleroderma

• Some chronic infections

Besides rheumatoid arthritis, which diseases can result in a positive RF test (4)

• Latex agglutination

• IgM

RF is done using (——) on a slide, and it detects only (——) isotype

• ELISA

• Nephelometry

When testing for rheumatoid arthritis, (—2—) are more sensitive and precise; they can detect IgG isotypes, which is more specific

ELISA

Anti-CCP testing is done using (——), which is a great test for early diagnosis where RF may be negative; a large number of RF-negative RA patients are anti-CCP positive