MIMM 214 - Innate Immunity (Lec 1-9)

Virus, parasite, bacterium, and fungus

What are the 4 diff pathogens?

Bone marrow, thymus, lymphatic system, and lymph nodes

What are the key components of the immune system?

Bone marrow & thymus

What are the primary lymphoid organs? (where immune cells develop)

Lymph nodes, spleen, and mucosal associated lymphoid tissues (malt)

What are the secondary lymphoid organs? (where immune response is generated)

Bone marrow

Where do leukocytes (WBC) originate from?

Arise from hematopoietic stem cells by hematopoeisis

What do mature blood cells arise from?

RBCs, granulocytes and megakaryocytes (platelets), monocytes, and macrophages

What comes from the myeloid lineage?

Neutrophils (NETs), basophils/mast cells (inflammation & allergies, histamine), and eosinophils (antiviral & anti-parasite activity)

What are the different granulocytes?

Migrate into tissues, differentiate into macrophages, destroy pathogens & present antigens

What are monocytes?

Specialized for phagocytosis & macrophages can also present antigens to T cells

What do macrophages & neutrophils do?

Dendritic cells

What are he most potent antigen-presenting cells for activating naïve T cells?

Immature dendritic cells capture antigen & then mature and migrate out of the location to present antigen to T cells

What do immature dendritic cells do?

B & T (CD4 helper and CDT cytotoxic) cells and and NK cells (innate lymphoid cell subtype)

Which cells develop from common lymphoid progenitor?

Clusters of differentiation

What differentiates lymphocytes?

BCRs can be bound to membrane or secreted as antibodies

How do B cell receptors work?

Always membrane bound

How do TCR’s work?

Dendritic cells are the bridge in the immune response -?antigen-presenting cells to T cells

Which cell comes from lymphoid and myeloid lineage?

Activation of innate immune system response produces signal molecules → they can communicate or mediate interactions → they trigger changes in target cell

How do signal molecules work?

Cytokines (messenger) and chemokines (recruit cells to a site)

What are secreted proteins?

Secreted proteins, receptors on the cell surface, intracellular signaling molecules & transcription factors and antigens

What are the key types of molecules?

Nucleic acid, polysaccharide, lipid, organic chemical, or drug

What can an antigen (Ag) be?

Macrophages, neutrophils, and dendritic cells

What are phagocytes?

Their PRRs (pattern recognition receptors) recognize PAMPs (pathogen-associated molecular patterns)

How do macrophages, neutrophils, and dendritic cells recognize pathogens?

Induces effector functions → phagocytosis → produce inflammatory mediators → cytokines and chemokines

What does PRR activation on sensor cells do?

Redness, heat, swelling, and pain → vasodilation & increased vascular dilation

What are hallmarks of inflammation?

Dendritic cells carrying antigen migrate vis lymphatic vessels to regional lymph nodes → activate naïve T cells

How is innate immunity linked to adaptive?

In lymph node

Where does B and T cell activation occur?

Epitope of antigen is presented using MHC (major histocompatibility complex, MHC) → interacts w/ TCR

How does antigen presentation work?

Antibodies secrete immunoglobin molecules which bind antigens (Ag)

What do antibodies do?

Circulating in serum (fluid part of blood)

Where are antibodies found?

Yes!

Can 2 antibodies (Abs) recognize different epitopes on the same antigen?

TCR can only see small pieces from Ag bound to MHC molecules of APCs and BCRs can see Ag in its natural form

Difference between TCR and BCR?

Rearranging and editing genomic DNA that encodes the antigen receptors by each B and T cell → potential to respond to any antigen that comes along

How do lymphocytes have such specificity?

If a lymphocyte reacts to self-antigen is is eliminated

How do we not attach self antigens?

Results in proliferation producing large numbers of clones

What happens when B or T cell interacts w/ its antigen?

They become effector cells and fight infections through humoral and cellular-mediated activities

What happens once B and T cells are activated?

Combats pathogens via antibodies

What is humoral immunity?

Involves primary T lymphocytes

What is cell-mediated immunity?

CD4 T cells activate B cells and macrophages and CD8 T cells kill infected cells directly

How does cell-mediated immunity work?

Involved in clearing and or neutralizing antigen (so it can’t bind to anything else)

How does humoral immunity work?

Activating your own immune response → natural is by natural infection and induced is via vaccination

What is active immunity?

Receive cells or molecules that mediate immunity → natural is IgA through breast milk → induced is getting someone else’s antibodies (monoclonal antibody therapy)

What is passive immunity?

Epithelial surfaces provide first barrier to infection → skin, gut epithelium, respiratory epithelium, mucosal membranes → acidic pH and antimicrobial peptides → saliva, hair, mucus, and tears all provide innate immunity

What is the 1st line of defense against infection?

Neutrophils & granulocytes, monocytes & macrophages (tissue residents), dendritic cells (activates by PAMP binding to PRR), NKs and ILCs

Innate immune cells?

Enzymes (lysozyme digests peptidoglycan), anti-microbial peptides (defensins disrupt cell membrane) and complement

Molecules in innate immunity?

Macrophages, neutrophils, and immature DCs → pathogens must bind to their receptors → remove & kill pathogens and make antigenic peptides to present to T cells

What are phagocytes and how are they activated?

Directly → PAMPs interact w/ PRRs

Indirectly → phagocytes recognize opsonins on microbial surface → enhances phagocytosis → opsonization

How does phagocytosis occur directly and indirectly?

PRRs bind to PAMPs → pseudopodia extend → engulfs and internalizes pathogen → lysosome fuses w. phagosome → phagolysosome has a low pH & antimicrobial peptides activate & pathogens are killed

What are the steps in phagocytosis for macrophages & dendritic cells?

Primary & secondary granules fuse w/ phagolysosome and release additional enzymes & antimicrobial peptides that attack the microbe

How does phagocytosis occur for neutrophils?

Antimicrobial proteins & peptides → low pH → hydrolytic enzymes → oxidative attack

How do phagolysosomes kill microbes?

Phagosome NADPH oxidase generates reactive oxygen species (ROS) → results in increase oxygen consumption and respiratory burst

How is oxidative attack caused?

Rapid release of reactive oxygen species → degrades internalized particles and bacteria in phagocytes

What is respiratory burst?

Pathogen killing, pathogen processing, pathogen presentation to sensory cytosolic receptors

Role of phagolysosome in innate immunity?

Antigen degradation, antigen processing, and antigen presentation

Role of phagolysosome in adaptive immunity?

Dead/dying cells express DAMPs and binds to PRRs

How do phagocytes clear up cells that have undergone apoptosis?

Express protein CD47 → binds to SIRPalpha on macrophages & phagocytosis is inhibited →

What do healthy erythrocytes express?

They express elevated levels of CD47

How do tumour cells avoid phagocytosis?

Capable of phagocytosis → recruited to the site of infection → produces NETs (neutrophil extracellular traps) → traps microorganisms & prevents spread

How do neutrophils work?

Macrophage of the brain cleans up myelin debris caused by multiple sclerosis → microglia required for CNS repair

How does CNS-resident microglia work?

Group of soluble proteins that cooperate w/ innate and adaptive immune system to eliminate pathogens, dying cells, and immune complexes from the body

What is the compliment system?

Proteases → enzyme that performs proteolysis → “C” or “factor”

What’s the most common type of compliment?

Liver

Where are compliment proteins mostly produced?

Increase vascular permeability, destroy pathogen cell membranes, & opsonization

Main roles of compliment?

Inactive pro-proteases

What are compliments initially?

Initially inactive pro-proteases → proteolytic cleavage (on inactive proteins) → generating 2 fragments → small one “a” with a specific function → big one “b” with proteolytic activity on a new substrate

How does compliment et activated?

They all generate C3 convertase (which cleaves C3 into C3a and C3b)

What do all 3 compliment activation pathways have in common?

Triggered by soluble proteins → lectins (PRR) → mannose-binding lectin (MBL) and ficolins → they recognize & bind carbohydrates on pathogen surface → C3 convertase is generated (C4b2a) → C3 cleaved into C3a and C3b

How does the lectin pathway work?

C1q binds antibodies bound to pathogen surface or pathogen surface directly → triggers signaling cascade on pathogen surface → C3 convertase (C4b2a) → C3 cleaved into C3a and C3b

How does the classical pathway work?

G1q binds to pathogen surface or to antibodies

How does classical pathway connect adaptive and innate immune system?

Enhances inflammation

What does C3a do?

Opsonization and is C5 convertase → C5 to C5a and C5b

What does C3b do?

1. Once C3b has been produced & lies on pathogen surface (via lectin or classical) → amplification loop for C3b formation (deposits more C3b on pathogen) → needs factor B and protease factor D → C3bBb (C3 convertase) → cleaves more C3 to make C3a and C3b (makes C3b in its own way)

How does the alternative pathway work? (#1)

2. High conc. of C3 → undergoes spontaneous hydrolysis which also involved factors B & D

How does the alternative pathway work? (#2)

C3bBb → lectin & classical pathways make C4b2a

What is the alternative pathway C3 convertase?

By factor called properdin (factor P) → secreted by neutrophils → factor P stabilized Bb and C3b together into C3bBb

How is C3bBb stabilized?

1. More signaling results in cleavage of other compliment molecules → C3a and C5a recruit phagocytes & promote inflammation
2. Compliment receptors connect compliment-tagged pathogens to effector cells → C3aR/C5aR on granulocytes → stimulates release of proinflammatory cytokines & granule component from basophils, eosinophils, neutrophils, and mast cells

How is inflammation a downstream effect?

Anaphylactic shock → they can bind to receptors on mast cells → release histamine

What can large amounts of C3a and C5a cause?

C3b binds to pathogen and phagocytes have receptors for C3b → opsonization of pathogen

How is phagocytosis increased?

Via compliment deposition and/or antibodies

What are 2 ways opsonization can occur?

C5 and C3 are involved in forming the membrane attack complex (MAC) → pore on the surface of a pathogen that lyses pathogen

How does pathogen lysis occur via compliments?

In plasma or cell surfaces prevent compliment activation from proceeding under normal circumstances:

* prevent C3 convertase from being generated
* promote disappearance of C3 convertase

How do compliment-regulatory proteins work?

C4b2a and C3bBb → turn C3 into C3a and C3b

What are the 2 forms of C3 convertase?

C3b is a C5 convertase → C5 into C5a and C5b

What does C3b do?

Recognize PAMPs → they are on hist cells, in host cells, or are host soluble proteins

What can PRRs be?

Damage associated molecular patterns are also recognized by PRRs

What are DAMPs?

All types of myeloid white blood cells and some lymphoid cells (NK cells)

Which cells have PRRs?

Cell surface, intracellular, secreted

Where are PRRs recognized?

TLRs, NLRs, RLRs, CLRs, and ficolins and MLB

What are types of PRRs?

Intracellular signaling which activates signaling pathway → leads to innate/inflammatory responses

What does PAMP binding cause?

Can be intra or extracellular → they correspond to the PAMPs they recognize → TLRs inside the nucleus bind to viral nucleic acids → extracellular TLRs bind to bacteria, fungi etc

What are TLRs?

Recruit adaptor proteins → they link protein-binding partners together and facilitated large signaling complexes

What does TLR activation do?

NF-kB transcription factor activation

Interferon regulating factor (IRF) pathway

MAP kinase pathway downstream transcription factors (AP-1)

What do adaptor proteins lead to?

Activation of transcription factors → transcription of innate/pro-inflammatory genes → once they get expressed they have specific impacts

What does TLR signaling lead to?

Phosphorylation is a key event → it leads to the activation of transcription factors → transcription

What happens one signaling cascade is triggered?

Adaptor proteins → MyD88 & TRIF

Transcription factors → IRF3/7, NF-kB, AP-1)

What are key adaptor proteins and transcription factors associated w/ TLRs?

Ligand binds to PRR → recruitment/activation of kinases and adaptors → second messenger → activation/nuclear translocation of transcription factors → changes in gene expression → post- transcriptional or post-translational modifications → functional response

What are the steps in signal transduction?

Only on plasma membrane, not in cytosol → binds carbohydrates on extracellular pathogens & some allergens → activated tyrosine kinases which trigger signaling cascades → induce the expression of inflammatory cytokines

How do CLRs work?

They are only intracellular in cytosol → target viral nucleic acids and proteins

Where are RLR and NLR proteins located?

Cytosolic PRRs → recognize viral dsRNAs (disk binds to dsRNA) → triggers MAVS (mitochondrial antiviral signaling protein) → gets activated & gets phosphorylated and transcription factors get activated → triggers signaling that activates IRFs and NF-kB (transcription factors) → goes into nucleus and expressed por-inflammatory response

How di RIG-I-like receptors work? (RLR’s)

Transcription factors

What are IRFs and NF-kBs?