Etiology & Pathophysiology 8% Flashcards
What are fibrous joints?
Bones connected by fibrous connective tissue with little to no motion
e.g. SI joints, sutures of skull
What are cartilaginous joints?
Bones connected by cartilage with little to no motion
e.g. intervertebral discs, pubic symphysis, sternomanubrial joints
What are synovial joints?
Bones connected by hyaline cartilage and separated by a joint space lined with synovium and filled with synovial fluid, allowing for FREE MOVEMENT
e.g. most joints
What factors contribute to joint stability?
Shape of joint
Joint capsule and ligaments prevent hypermobility
Muscles and tendons actively guide and stabilize
Adhesive properties of synovial fluid
What types of cells make up the synovial membrane?
Type A synovial membrane cells (20%)
Type B synovial membrane cells (80%)
Synovial membrane is the same thing as synovial lining or synovial intima.
What are Type A synovial membrane cells?
Macrophages
20% of synovial membrane cells
Express CD45, MHC class II, CD68 - macrophage cell surface markers
Remove debris from synovial space
What are Type B synovial membrane cells?
Fibroblasts
80% of synovial membrane cells
Produce matrix components
What are the principle components and functions of synovial fluid?
Synovial fluid is a filtrate of plasma with similar concentrations of small molecules and lower concentrations of large molecules (e.g. proteins)
Functions to lubricate and allow free movement
Does not have any components of coagulation pathway. Doesn’t clot.
Albumin 1.2 g/dL
Total protein 1.7-2.1 g/dL
IgG 13% of serum, igM 5% of serum
Hyaluronic acid 300 mg/dL - provides viscosity
What are the principle components of articular cartilage?
Chondrocytes - derived from MESODERM
Extracellular matrix components
How is articular cartilage organized?
Into cartilage ZONES
Zone 1: most superficial and contacts synovial lining. Chondrocytes in zone 1 synthesize LUBRICIN. More cellular in zone 1.
Zone 2
Zone 3
Zone 4: separated by zone 3 by “tidemark” a blue line on H&E. Where calcification of matrix starts.
What do chondrocytes of the articular cartilage synthesize?
Chondrocytes of the articular cartilage synthesize:
- Proteoglycans and collagen of the extracellular matrix
- Proteases to degrade ECM components to maintain cartilage regulation
What are the principle components of the extracellular matrix of articular cartilage?
Proteoglycans - protein core to which glycosaminoglycans (chondroitin sulfate and keratan sulfate) attach. Primary proteoglycan is aggrecan.
Collagens
- Type II collagen
- Type IX, Type X collagen
What are the classifications of bone based on mechanism of ossification?
Intramembranous ossification - facial, cranial, clavicular bones
Endochondral ossification - mostly appendicular and axial skeletal bones
What is bone matrix primarily made of?
90% Type I collagen
What cells make and degrade bone?
Mesenchymal stem cells
Osteoblasts
Osteocytes
Osteoclasts
What is the function of mesenchymal stem cells?
Differentiate into cells of bone (osteoblasts, osteocytes, osteoclasts), cartilage (chondrocytes), muscle (myocytes, or fat (adipocytes)
Located in inter-trabecular loose connective tissue next to vascular channels and in the periosteum
What is the function of osteoblasts?
Produce organic components of bone, mainly COLLAGEN but also OSTEOCALCIN and OSTEOPONTIN
After becoming entrapped in formed bone, become OSTEOCYTES within lacunae
What is the function of osteocytes?
Mineralizes hydroxapatite, bone’s organic matrix
Most abundant bone cell that preserves bone integrity and mediates remodeling in response to mechanical stress
Connected by cytoplasmic tendrils that deliver nutrients and metabolites to keep the osteocytes alive
What is the function of osteoclasts?
Bone resorption
Converts trabecular bone to compact bone
Degrade bone by secreting lysosomal enzymes that cause Ca release
What are the differences between cortical (compact) and trabecular (cancellous, spongy) bone?
Cortical (compact) bone - outer layer of thick cortical bone
Trabecular (cancellous, spongy) bone - inner layer of interlacing ossified trabeculae. Alignment of trabecular network with long axis of the bone confers maximal tensile strength and compressive tolerance so that less bone mass is required
Bones subject to mostly tensile and compressive forces (e.g. vertebrae) have thin cortical bone and exert their support by their shape and trabecular architecture
Bones subject to torsion, bending, and shearing forces (e.g. bones of the leg) are usually cylindrical with thick collar of cortical bone and a marrow cavity
What type of collagen is bone predominantly made of?
Type 1 collagen (bONE)
What type of collagen is articular cartilage predominantly made of?
Type 2 collagen (carTWOlage)
What type of collagen is the glomerular basement membrane predominantly made of?
Type 4 collagen (basement has a floor = four)
What is a DEXA scan?
Dual Energy X-ray Absorptiometry
- preferred methods for measurement of bone mineral density (BMD)
- lowest radiation (1/10th of CXR)
- need to adjust for bone size
- osteopenia z score -1 to -2.5
- osteoporosis z score < 2.5
What enzyme is released during osteoblast activity (bone formation)?
Alkaline phosphatase
80% of alk phos in children is from bone. The rest is from liver, gut, kidneys.
What protein is secreted into bone extracellular matrix and correlates with bone formation?
Osteocalcin
What is a cleavage product of collagen synthesis and correlates with the number of collagen fibrils formed?
Procollagen type I carboxy-terminal propeptides
What ratio is increased with bone resorption?
Increased urinary Ca:Cr ratio
What enzyme is released during osteoclast activity but is not specific for it?
Tartrate-resistant acid phosphatase (TRAP)
What amino acid is present in mature collagen and is released with breakdown of collagen in bone and other connective tissue but is not specific for it?
Hydroxyproline
What stabilizes mature collagen and is released during matrix resorption?
Collagen crosslinks of pyridoline, deoxypyridinoline-more specific for bone
What are the N-terminal (Ntx) and C-terminal (Ctx) collagen telopeptides?
Markers of bone resorption
Ntx more sensitive and measurable in urine
Anaphylaxis, allergic rhinitis, allergic asthma are examples of what type of hypersensitivity reaction?
Type I (immediate)
IgE induced mast cell activation
Basophils and mast cells involved
Autoimmune hemolytic anemia, chronic urticaria, Goodpasture syndrome is an example of what type of hypersensitivity reaction?
Type II (cytotoxic)
IgG and IgM autoantibodies
Complement activation and complement mediated phagocytosis
NK cells, eosinophils, neutrophils, macrophages
Serum sickness, PSGN, LN are examples of what type of hypersensitivity reaction?
Type III (immune complex)
Deposition of antibody-antigen complexes causing tissue damage
Neutrophils involved
Contact dermatitis, RA, MS, Crohn disease are examples of what type of hypersensitivity reaction?
Type IV (delayed)
T cell mediated inflammation of cytotoxicity
What increases bone mineral density?
weight bearing exercise
What is the structure of collagen?
Extracellular structural protein with 3 alpha chains assemble into a triple helix
What amino acids are highly expressed in collagen? There are 3.
Has a high proline, hydroxyproline and glycine content which occupies every third amino acid position. Most proline in sequence of Gly-Pro-Xaa (unspecified AA, often alanine or hydroxyproline).
What are endopeptidase enzymes that cleave by hydrolyzing peptide bonds in the middle of molecules are integral to bone and cartilage homeostasis?
Proteinases
Which endopeptidases act in neutral pH?
Serine and metalloproteinases
What endopeptidases act in acidic pH?
Aspartate, cysteine and threonine proteinases
What leads to increased rigidity and decreased tensile strength with age?
Increased stable cross-linking of collagen fibers
What factors control the degradation of proteoglycans and hyaluronic acid?
Metalloproteinases, adamtss and cysteine proteinases degrade proteoglycans. Fragments are endocytosed and further degraded in lysosomes. Also cathepsin activity.
What enzyme degrades hyaluronic acid?
Hyaluronidase
What constituent of the connective tissue is described below:
Lack tensile strength but can stretch. Produced by fibroblasts and by smooth muscle cells.
In ligaments, blood vessels, lungs and skin allowing these to return to original shape after stretch
Degraded by elastase in the pancreas, macrophages, leukocytes and platelets
Is a serine protease
Contribute to aneurysm formation during vasculitis
Elastin
What constituent of the connective tissue is described below:
Dimeric glycoprotein that acts as an attachment protein in the ECM. Produced by many cells and binds to collagens, proteoglycans, fibrinogen, actin, cell surfaces and bacteria.
Between basements membranes and cells. In plasma as insoluble matrix through loose conn tissue.
Binds VLA4, an adhesion molecule on inflammatory cells such as activated T cells
Fibronectin
What constituent of the connective tissue is described below:
Major constituent of the basement membrane with type IV collagen
Laminin
Where does early B cell development occur?
Bone marrow
What must occur for pro-B cells to become pre-B cells?
VDJ and VJ recombination of heavy and light chains of immunoglobulin
What does a pre-B cell express on the cell surface to acquire Ag specificity and become an immature B cell?
A unique B cell receptor (BCR)
Surface IgM
What are the 3 processes by which a B cell acquires central tolerance?
Receptor editing by secondary rearrangement of the IgX allele
Clonal anergy - B cells that react with low acidity to self Ag can migrate into the spleen as anergic cells
Clonal deletion - for cells that fail receptor editing
Immature B cells that survive central tolerance turn into ___ that then turn into ___ and ___with Ag engagement.
Immature B cells that survive central tolerance turn into naive B cells that then turn into memory or high affinity plasma cells that make Ab with Ag engagement.the plasma cells occur as a result of somatic hyper mutation, clonal expansion, class switching recombination in the germinal center
What does the innate immune system recognize?
The innate immune system recognizes molecular structures that are produced by microbial pathogens.
PAMPs and DAMPs
What are the functions of pattern recognition receptors (PRRs)?
Toll-like receptors (TLRs) are a large class of PRRs expressed on plasma membrane and in endosomes
TLR2 - targets are peptidoglycans (gram positive bacteria) and envelope glycoproteins (viruses)
TLR4 - targets LPS (gram negative bacteria), HSP60 (chlamydia pneumonia), RSV fusion protein
TLR 9 - targets unmethylated CG-rich (CpG) oligonucleotides
TLRs recognize pathogenic micro-organisms and activate antimicrobial defenses
The major signal transduction pathway that TLRs engage to activate cells = NF-KB
PRRs recognize PAMPs
PAMPs bind to TLRs -> receptor oligomerization -> downstream cell signaling -> activates inflammatory pathways within cells (ie. NF-kB)
What is the function of mannose (lectin) receptors on phagocytes?
Phagocytes (neutrophils and macrophages) use surface receptors, including mannose receptors and scavenger receptors, to recognize extracellular bacteria, and they use Fc receptors and complement receptors to recognize bacteria opsonized with antibodies and complement proteins, respectively.
Mannose receptors function mainly to promote phagocytosis of the microbe
Phagocytosis can be enhanced by coating the microbe with IgG antibodies, C3 and other plasma proteins = opsonization
What immune cell produces IFN-gamma? What cell of the innate immune system is activated?
Th1 cells produces IFN-gamma
IFN-gamma is a potent activator of macrophages
What is the immune defect in chronic granulomatous disease?
Inherited deficiency of one of the components of phagocyte oxidase. This deficiency compromises the capacity of phagocytes to kill certain bacteria.
How do NK cells kill viral-infected cells?
Direct action of NK cells: NK cells have granules containing proteins that mediate killing of target cells
When they recognize a virus infected cell and are then activated, they secrete these granules, such as perforin, which puncture the infected cell and release granzymes into the infected cells which cause the cell to undergo apoptosis.
What cytokines do NK cells secrete?
Mainly TNF-alpha and IFN-gamma
which act on other immune cells like macrophages and DCs to enhance the immune response
Produce high levels of IFN-gamma (a potent stimulator of macrophages), TNF-alpha, GM-CSF, and other cytokines and chemokines
In turn, activated macrophages produce IL-12, a potent inducer of NK cell, IFN-gamma, and cytolytic activity
Additional cytokines secreted include IL-17, IL-22
How do NK cells kill target cells?
NK cells release cytotoxic granules containing perforin and granzyme, which leads to lysis of the target cell
What are the 4 functions of complement proteins?
Promote phagocytosis of microbes by opsonization (C3b has the most opsonizing activity)
Complements bind antigen-antibody complexes promoting their solubilization and their clearance by phagocytosis
Stimulation of inflammation - by attracting macrophages and neutrophils
Induction of lysis of microbes
What cells produce complement proteins?
The liver is the primary source of plasma complements, hepatocytes make most of the proteins and glycoproteins. Tissue macrophages, blood monocytes, and epithelial cells of the GU and GI tract.
What inhibits C1r and C1s?
C1 inhibitor - serine protease inhibitor.
C1 INH prevents the C1r/C1s complex from starting the proteolytic cascade and causes the complex to dissociate from C1q, creating a time dependent period for C1r/C1s to be activated before being automatically removed
Deficiency of C1 INH leads to hereditary angioedema where you get activation of bradykinin leading to vascular permeability
What inhibits C3 and C5 convertase?
C3b and C4b, which are found on cell surfaces
What inhibits the assembly of MAC complex?
CD59 membrane protein
S protein in the blood
What chromosome is MHC complex located on?
Chromosome 6
What are the most common positive acute phase reactants?
Procalcitonin, CRP, ferritin, fibrinogen, hepcidin, serum Amyloid A, haptoglobin, complement (C3, C4)
Angiotensinogen, alpha-1-acid glycoprotein, lipopolysaccharide-binding protein (LBP), alpha-1-antitrypsin, vitronectin, ceruloplasmin, alpha-1 macroglobulin
What are negative acute phase reactants? (decrease with inflammation)
Albumin, prealbumin, transferrin, retinol-binding protein, antithrombin
What is a marker for macrophage activation?
Neopterin is specifically produced by human monocytes/macrophages when stimulated by IFN-gamma released from activated T cells
Studied in MAS/HLH, AIBD, JDM
What part of innate immunity does C-reactive protein activate?
C reactive protein is a plasma protein and part of a group of proteins called penntraxins
Penntraxins recognize phospholipids (i.e. phosphorylcholine) found only on bacteria, and bind C1q and initiate the COMPLEMENT CLASSICAL PATHWAY
Interacts with phagocyte C1q receptors and binds directly to the Fc gamma receptors
What are the pro-inflammatory cytokines?
IL-1alpha, IL-1beta, TNF-alpha, IL-6, IL-17, IL-22
What are anti-inflammatory cytokines?
IL-10, TGF-beta
What cytokines are produced by T helper (Th2) cells?
IL-4, IL-5, IL-13
What cytokines are produced by Tregs?
IL-10 and TGF-beta (anti-inflammatory)
What does interferon-alpha do?
activates NK cells and increases MHC type 1 presentation, antiviral state, and has multiple other effects (especially in SLE)
Which cytokines influence bone destruction?
TNF-alpha, IL-1, IL-6, IL-7, and IL-17
In inflammatory bone disorders (JIA, RA), elevated inflammatory cytokines have been implicated in bone destruction through recruitment of osteoclast precursors to the bone environment, where they differentiate into mature osteoclasts
These inflammatory cytokines, such as TNF-alpha, IL-1, IL-6, IL-7, and IL-17, are responsible for the overexpression of RANKL and decreased levels of osteoprotegerin (OPG), a decoy receptor of RANK.
This perturbation leads to an imbalance in the RANKL/OPG ratio, thereby increasing osteoclast differentiation (also known as osteoclastogenesis)
What stimulates Type 1 IFN production? What is the function of Type 1 IFN?
Type 1 IFN - produced by most cells upon stimulation by a virus (leukocytes, plasmacytoid DCs, Fibroblasts); primary function is to induce viral resistance in cells
Inhibit viral replication, increase the lysis potential of NK cells and expression of MHC class I molecules on viral infected cells, stimulate the development of Th1 cells
IFN-alpha
IFN-beta
What size molecules are removed by dialysis? (for Katie)
All molecules in plasma > 15 kD
What cytokine activates B cells to antibody producing plasma cells and induces Th17 differentiation?
IL-6
Which interleukins influence fibrosis?
Th2-derived cytokines (IL-4, IL-5, IL-6, IL-13, and IL-21) have a distinct role in the regulation of organ fibrosis
Especially IL-6
What are the roles of antibodies?
Pathogen and toxin neutralization
- IgG in blood and tissues
- IgA in gut lumen
Classical complement activation/fixation
- IgG1, IgG3, IgM
Opsonization to promote phagocytosis and pathogen elimination
Antibody-dependent cellular cytotoxicity
- IgG binds infected cell to be killed by NK cells
What are the principles of humoral immunity?
Humoral immunity encompasses aspects of the immune system mediated by antibodies, complement proteins, and certain antimicrobial proteins (AMPs) found in the extracellular fluid
Humoral immunity refers to antibody production and the coinciding processes that accompany it, including:
- Th2 activation and cytokine production
- Activation of specialized antigen-presenting cells leading to…
- Germinal cell reaction leading to…
- Generation of long lived plasma cells and memory B cells.
- Isotype switching of B cells
- Affinity maturation and memory cell generation
What is the germinal center reaction?
The GC reaction occurs in response to protein antigen and has several outcomes:
Antibody affinity for antigen increases.
B cells differentiate into long-lived plasma cells that secrete antibodies.
B cells differentiate into memory B cells that can generate more plasma cells.
There is isotype switching at the immunoglobulin genes to create IgA, IgG, or IgE antibodies with the same antigen specificity as the original IgM.
What is isotope switching?
Generation of different antibody isotypes (IgGAME) that contributes to effective immunity.
B cells undergo isotype switching at the immunoglobulin genes in response to T cell signals in the GC reaction.
There is isotype switching at the immunoglobulin genes to create IgA, IgG, or IgE antibodies with the same antigen specificity as the original IgM.
Isotype switching alters the antibody heavy chain but does not affect antibody affinity for antigen.
Isotype switching involves the cutting and rearranging of DNA.
What are the roles of B cells?
B cells differentiate into plasma cells that secrete antibodies
B cell affinity maturation so that they make antibodies with higher affinity
B cells differentiate into memory B cells that. can generate more plasma cells
What is the structure of IgG?
Monomer with 2 heavy chains paired with 2 light chains that create the constant fragment (Fc) and 2 identical variable Ag binding fragments (Fab)
What is the function of IgG?
Workhorse of humoral immunity
Main Ab of secondary responses
Activates phagocytosis by opsonization - Fc binds to phagocytes
Neutralizes Ag
What is the structure of IgA?
Dimer
What is the function of IgA?
Protects mucosal surfaces
Protease-resistant
Functions in the gut as well
What is the structure of IgM?
Pentamer
What is the function of IgM?
First Ab produced during an immune response
Activates complement
Low affinity but high avidity
The monomer form of IgM serves as a B cell receptor
What is the structure of IgE?
Monomer
What is the function of IgE?
Destroys parasitic worms (extra-cellular parasites)
Involved in allergy and response to helminths (worms)
What is the structure of IgD?
Monomer
What is the function of IgD?
B cell receptor
Activation of IgD is an important B cell survival signal
What cytokine signal causes proliferating B cell to differentiate into a plasma cell that makes IgG2 or IgG3?
IFN-gamma
What cytokine signals cause proliferating B cell to differentiate into a plasma cell that makes IgE?
IL-4, IL-5
What cytokine signal causes proliferating B cells to differentiate into a plasma cell that makes IgA?
TGF-beta
What cytokine signals causes proliferating B cell to differentiate into a plasma cell that makes IgM?
IL-2, IL-4, IL-5
What 2 signals/interactions must occur to activate a T helper cell?
APC Th cell
- MHII-Ag T-cell receptor
- B7 CD28
What happens when an activated T helper cell secretes cytokines?
Class switching
What to signals/interactions must occur to activate a B cell to proliferate, differentiate, and secrete Abs?
Activated Th cell B cell
- T cell receptor MHC II-Ag
- CD 40 ligand. CD 40
What is somatic mutation in the context of humoral immunity?
Somatic hypermutation involves a programmed process of mutation affecting the VARIABLE REGION OF IMMUNOGLOBULIN GENES. Unlike germline mutation, SHM affects only an organism’s individual immune cells, and the mutations are not transmitted to the organism’s offspring. Mistargeted somatic hypermutation is a likely mechanism in the development of B-cell lymphomas and many other cancers.
SHM diversifies B cell receptors used to recognize new Ag and allows the immune system to adapt its response to new threats during the lifetime of an organism.
What is affinity maturation?
Affinity maturation is a coordinated process with distinct stages including:
migration of B-cells to secondary lymphoid organs where
- B-cells proliferate in germinal centers to form a colony
- the B-cell receptor is randomly mutated in different cells
selection of the cells with the highest affinity receptors within the colony by
- providing a limited number of survival signals
- allowing mutated B-cells to compete for these signals
- pruning less effective B-cells through apoptosis
What anti-inflammatory cytokines do B regulatory cells (Bregs) release?
IL-10, IL-35, and TGF-β
Bregs also interact directly with T cells to encourage differentiation into Tregs
Know the general structure, size, and organization of the human genome
3.2 billion deoxyribonucleic acid (DNA) base pairs
23 pairs of chromosomes
over 44,000 genes
Know how genes are organized (e.g., introns, exons, promoters, and enhancers)
Exons: gene segments that encode protein sequences
Introns: do not encode protein sequences
How are genes regulated by epigenome?
The epigenome is involved in regulating gene expression, development, tissue differentiation, and suppression of transposable elements The epigenome can be dynamically altered by environmental conditions.
What is the most predominant isotype of antibody secreted by Plasma B lymphocytes?
IgG
Plasma B lymphocytes secrete large quantities of antibodies. The most predominant isotype in the blood and extracellular fluid is IgG.
What Isotype are the pathogenic antibodies in lupus patients against double-stranded DNA?
IgG
Pathogenic antibodies in lupus patients against double-stranded DNA are mostly of the IgG isotype
What cytokines would be used by the body to clear a pinworm infection?
IL-4 and IL-5
Pinworms are parasites. Eosinophils are recruited to the sites of infection and inflammation to help clear the worms. Cytokines involved in the parasitic inflammatory response include IL-4 and IL-5. In particular, IL-5, also called eosinophil differentiation factor, is produced in response to a parasitic infection and is mainly responsible for the growth, activation, and differentiation of eosinophils.
What type of T cell is needed to protect against intracellular pathogens like mycobacteria or salmonella?
Th1 T cells
Th1 T cells produce interferon-γ and induce killing of intracellular pathogens such as mycobacteria or Salmonella.
What cells produce INF-gamma to activate macrophages to produce reactive nitrogen species and kill intracellular bacteria and fungi?
Th1 CD4+ T cell
What cells produce IL 4 and IL 5?
Th2 CD4+ T cell
Which T cells and interleukins are important for allergy and eosinophils?
Th2 CD4+ T cell
IL4 makes IgE
IL 5 activates eosinophils
What T cell and interleukin defends against extracellular bacteria and fungi?
Th17 CD4+ Tcell
IL 17 induces neutrophil rich inflammation
What cells and targets are important for peripheral tolerance?
Treg C4+ T cel
expresses CTLA-4 and TGF-betta to suppress auto reactive T cell
What cells lyse virus infected cells expressing viral antigens?
CD8+ T cell
What type of hypersensitivity reaction is described below:
drug-IgE complexes that bind to mast cells and release histamine and inflammatory mediators
Type I reactions (IgE-mediated)
Type I reactions (IgE-mediated), such as drug-IgE complexes that bind to mast cells and release histamine and inflammatory mediators
What type of hypersensitivity reaction is described below:
specific IgG or IgM antibodies directed at drug hapten-coated cells
Type II reactions (cytotoxic)
Type II reactions (cytotoxic), such as specific IgG or IgM antibodies directed at drug hapten-coated cells
What type of hypersensitivity reaction is described below:
tissue deposition of drug-antibody immune complexes with activation of complement and inflammation
Type III reactions (immune complex), such as tissue deposition of drug-antibody immune complexes with activation of complement and inflammation
What type of hypersensitivity reaction is described below:
MHC presentation of drug molecules to T cells with release of cytokines and inflammatory mediators
Type IV reactions (delayed, cell-mediated), such as MHC presentation of drug molecules to T cells with release of cytokines and inflammatory mediators
