Immuno Exam 3

What is hematopoiesis?

Formation of blood cellular components

What are hematopoietic stem cells (HSCs)? What is their broad categorization?

Cells that can differentiate into many types of blood cells, also categorized as “pluripotent stem cells”

Neutrophils and macrophages are ___ ___. (What is their job?)

Professional phagocytes

What cell types can phagocytose, but only as a secondary function?

Eosinophils and basophils

How do neutrophils destroy microbes following phagocytosis?

Respiratory burst

Lytic enzymes & other antimicrobial compounds in neutrophil granules

Neutrophil Extracellular Traps (NETs)

What are Neutrophil Extracellular Traps (NETs) made of?

Sticky DNA containing antibacterial molecules

What are the tradeoffs with macrophages’ abilities?

They move slowly, but are more powerful phagocytes than other cells.

What are macrophages’ abilities?

Phagocytes

Contain cytoplasmic granules and can be activated

Some can divide and have extensive cytoplasmic processes

Can trigger tissue repair and wound healing

What can kill bacteria that defeat neutrophils?

Macrophages

Where are macrophages located?

Tissues, bloodstream

Where do most macrophages come from?

Bone marrow

What are the two types of macrophages, and what are their roles?

M1 - Destructive, aggressive phagocytes

M2 - Remove dead/dying cells, repair tissues

How are M1 macrophages specialized/activated?

Innate step: TLRs/PRRs stimulated by microbial products — Causes increased lysosomal enzymes, phagocytosis, membrane receptors, and protease secretion.

Full M1 Activation: Synergized by interferon-gamma

What characteristics increase in activated M1 macrophages?

Increased:

• size

• movement

• membrane activity

• lysosomal enzymes

• phagocytosis

• bactericidal activity

• MHC class II expression

• no production

What are the characteristics of activated M2 macrophages?

Increased:

tissue repair

MHC class II

Reduced microbial killing

How are resting macrophages specialized/activated into M2 macrophages?

Using anti-inflammatory cytokines like IL-4, IL-13, and IL-10

What are the three professional antigen presenting cells? Which is the best?

Dendritic cells (the best), B cells, and macrophages.

Dendritic cells activate what states of T cells?

All states, including naive T cells

What cells are excellent at presenting soluable protein antigens present in low concentrations to non-naive T cells?

B cells

What cells are good at presenting particulate antigens to non-naive T cells?

Macrophage

APCs have what imperative molecules?

MHC I and II, and co-stimulatory molecules

What are the cardinal signs of inflammation?

Rubor (redness)

Calor (heat)

Tumor (swelling)

Dolor (pain)

Loss of function (pain and neurological reflex)

What causes redness and heat at sites of inflammation?

Tissue damage triggers the release of vasoactive molecules (like histamine and prostaglandins), causing increased blood flow, and then redness/heat.

How is swelling caused in the body?

Tissue damage causes release of vasoactive molecules, which causes increased vascular permeability. It also triggers release of chemotactic molecules, causing neutrophil emigration. Both processes lead to swelling of tissues.

Pain is caused by:

Nerve damage and tissue damage causing the release of vasoactive molecules.

What are chemokines?

Proteins released by immune and non-immune cells to attract immune cells to the inflammatory locus

What are cytokines?

Proteins secreted by immune and non-immune cells to communicate among themselves. They are both inflammatory and anti-inflammatory.

What are some examples of lipid mediators that serve as biochemical mediators of inflammation?

Thromboxanes

Prostaglandins

Leukotrienes

What is an example of an enzyme that serves as a biochemical mediator of inflammation?

Matrix metalloproteinases

What DNA serves as a biochemical mediator of inflammation?

Mitochondrial and genomic DNA of neutrophils

What modified amino acids serve as biochemical mediators of inflammation?

Histamine, kynurenine, etc.

What are two discussed examples of eicosanoid signaling molecules made by fatty acids?

Leukotrienes and prostaglandins

What are leukotrienes and prostaglandins produced by?

Granulocytes, macrophages, mast cells, platelets, and endothelial cells

Leukotrienes and prostaglandins have what kind of effects (on other cells)? (hint: think “___-crine”)

Paracrine and autocrine

What do leukotrienes and prostaglandins do in the bloodstream?

Promote vascular permeability and dilation, platelet aggregation, and chemotaxis

How does inflammation affect vasculature/blood supply? (Think about how things move out of the vasculature)

Increases vascular permeability

Increases exudation

Increased expression of cell adhesion molecules

Inflammatory cytokines produced

What is exudation?

Fluid, proteins, RBCs, and WBCs escape from blood vessels, possibly causing edema/hemorrhage/triggers pain receptors.

What systems are activated in sites experiencing acute inflammation?

Soluable mediators are produced by various cell types.

Complement activation, activation of the kinin system, coagulation system, and fibrinolysis system.

How do neutrophils emigrate from blood vessels to tissues?

Neutrophils normally circulate within the bloodstream and bounce off the walls of healthy vessels.

In inflamed tissues, blood vessel walls become sticky and neutrophils stick to vascular endothelium. This relationship is mediated by integrins and selectins.

Systemic effects of acute inflammation are mediated by what molecules? What do they induce production of?

Proinflammatory cytokines; induce production of acute phase proteins (APPs) by the liver

What symptoms can be caused by systemic effects of acute inflammation?

Fever, leukocytosis, anorexia, lethargy, cachexia, and hemodynamic changes (shock)

Activation of the complement pathway causes what three main outcomes?

1. Inflammation

2. Phagocytosis of bacteria

3. Direct killing of bacteria

What are the two ways the complement pathway can be initiated?

Classical and alternate pathways

The classical pathway employs what complexes to activate complement?

Antigen-antibody complexes

The alternate pathway uses what to activate complement?

The bacterial surface (opsonization)

What is the difference between cytokines and hormones in their sources and targets?

Hormones have specific sources in the endocrine system, and specific cell targets.

Cytokines are produced by many cell types and target many cell types (pleiotropy).

What is the difference between cytokines and hormones in their redundancy?

Hormones have little to no redundancy. Cytokines have high redundancy.

What effect (“___-crine”) do hormones have on cells? What about cytokines?

Hormones are strictly endocrine, while cytokines have autocrine, paracrine, and endocrine effects.

What is the function of hormones? What are the functions of cytokines?

Hormones: Homeostasis in the body

Cytokines: Inflammation, immune response, tissue repair

What are some examples of hormones? Cytokines?

Hormones: Insulin, GnRH

Cytokines: Interleukins, Interferons, and Chemokines

What is the role of a primary lymphoid organ?

Lymphocyte generation and maturation

What is the role of a secondary lymphoid organ?

Site of antigen encounter and immune response

What are some examples of primary lymphoid organs?

Thymus, Bursa of Fabricius, bone marrow in primates and rodents, Peyer’s patches in ruminants

What are some examples of secondary lymphoid organs?

Lymph nodes, spleen, MALT (mucosa-associated lymphoid tissues), Peyer’s patches in non-ruminants

Are primary lymphoid organs antigen-dependent? How about secondary lymphoid organs?

Primary are antigen-independent. Secondary are antigen dependent.

What is the effect of removal of a primary lymphoid organ?

Severe, early, lifelong immunodeficiency

What is the effect of removal of a secondary lymphoid organ?

Milder than primary — other secondary lymphoid organs can compensate for lost function.

Why do APCs require MHC II and costimulatory molecules?

They are necessary to fully activate a helper T cell

What must happen for a B cell to be activated?

1. Antigen must bind to the BCR

2. Costimulation from helper T cells and their cytokines, as well as complement and PRRs

What cytokines can be used to signal for T cell help (during B cell activation)?

IL-4, IL-5, IL-6, IL-13, and IL-21 from Th2 cells

What cell to cell signaling pairs are involved in recruiting a T cell to help in B cell activation?

Pair 1:

• CD40 on resting B cells

• CD154 (CD40L) on activated helper cells

Pair 2:

• CD86 (B7) on activated B cells

• CD28 on T cells

How does this pairing function to help recruit T cells during B cell activation?

• CD40 on resting B cells

• CD154 (CD40L) on activated helper cells

1. T cell is activated via CD28-CD86 engagement, and rapidly upregulates CD154 (CD40L) on membrane

2. CD154 (CD40L) binds to CD40 on the B cell

How does this pairing function to help recruit T cells during B cell activation?

• CD86 (B7) on activated B cells

• CD28 on T cells

1. Resting B cell binds antigen, presents peptides on MHC class II to TCR

2. Upon TCR/MHC II recognition, B cell upregulates CD86 (B7)

3. CD86 binds to CD28 on helper T cell

What chains are required for cell-surface expression of BCR, and signaling through it? Why?

Ig-alpha and Ig-beta (which make up CD79); the intracytoplasmic region of the BCR heavy chain is too short to transduce a signal

What are ITAMs?

Immunoreceptor tyrosine activation motifs, they are located on the cytoplasmic domains of Ig-alpha and Ig-beta and carry signals of BCR

How is BCR signaling initiated? (Different from B cell activation)

Crosslinking of adjacent BCRs by an antigen — AND co-stimulation!!

What are plasma cells?

Terminally differentiated B cells. Secrete antibodies (immunoglobulins).

Few B cells respond in a primary antigen response. Between primary and secondary antigen responses, what happens with memory B cells?

They accumulate and greatly enhance subsequent reactions.

What is caused when plasma cells become cancerous?

Myelomas

Are antibody heavy chain constant regions usually different within the same animal?

No — they are very similar in the same animal, and even between individuals of the same species.

How do antibody light chain variable regions differ between cells?

Antibodies from different B cells/plasma cells have different VL.

Antibodies from the same B cell or daughter B cells have identical VL.

How do antibody light chain constant regions differ between cells?

They have kappa or lambda light chains.

Antibodies from the same animal have very similar CL based on isotype.

How do antibody heavy chain variable regions differ between cells?

Antibodies from different B cells/plasma cells have very different VHs.

Same B cells or daughter cells have identical VH.

Why are VHs on antibodies the same between B cells and daughter cells of an organism?

It’s necessary for keeping the same antigen specificity across generations.

How many heavy chain constant region isotypes are there?

Five major isotypes, plus several isotype subtypes

What determines helper T cell subpopulations? In other words, what determines T cell polarization? What does this result in?

Cytokine mixtures produced by antigen presenting cells. This causes helper T cells to each produce their own cytokine mixture.

What is the significance of the diversity in cytokine production of helper T cells?

It induces different forms of adaptive immunity/immune regulation

What do cytokines produced by Th1 cells influence?

Cytotoxic T cell and M1 macrophage responses

T cell activation requires both antigen and co-stimulatory signals. What happens when there’s no antigen?

No response

T cell activation requires both antigen and co-stimulatory signals. What happens when there’s no co-stimulation?

The T cell isn’t activated, and becomes unresponsive (anergy/peripheral tolerance)

What enzymes are required in the generation of diversity of B cells and T cells?

RAG-1, RAG-2, DNA-PK, and TdT

What do recombination-activating genes 1 and 2 (RAG-1 and RAG-2) do for B cell and T cell diversity?

Short answer: they recombine gene segments to make functional TCR and BCR

Long answer (what’s on the slide): They recognize conserved heptamer and nonamer sequences of recombination signal sequences adjacent to the V, D, and J genes. They also bring together distant exons.

What does DNA-dependent protein kinase (DNA-PK) do for B cell and T cell diversity?

Cleaves the DNA at recombination signal sequences

What does terminal deoxyribonucleotidyl transferase (TdT) do for B cell and T cell diversity?

Fills in the gap made by cleaving DNA by adding N nucleotides.

What are the mechanisms of specificity and diversity of B cells after gene rearrangement?

Somatic hypermutation

Gene conversion

What are the mechanisms of specificity and diversity of B cells during gene rearrangement?

• Multiple germ-line segments used to encode V, D, and J regions (genetic diversity)

• Combinatorial diversity in V-D-J joining

• Junctional flexibility: mutations, deletions

• P- and N- nucleotide additions

• Combinatorial association of heavy and light chains

How does TCR diversity arise? In what organ does it occur?

Via gene arrangement in the thymus:

• Combinatorial diversity - V-D-J recombination

• Junctional diversification

• Many variable genes, few constant genes

What are superantigens?

Antigens that crosslink nonspecific TCR and MHC, and do not fit in the MHC binding groove. Can activate up to 20% of body’s T cells, possibly causing toxic shock syndrome.

What is a classic example of a superantigen?

Staphylococcus aureus toxic shock syndrome

What cells use cytotoxic mechanisms to kill invaders?

Cytotoxic T cells, Natural Killer cells, Eosinophils, and sometimes antibodies participate

What do cytotoxic T cells and natural killer cells target?

Viruses, tumor cells, intracellular organisms

What do eosinophils target in the context of their cytotoxicity?

Parasites and other invaders too large to phagocytose

How can antibodies be cytotoxic (what is the mechanism called)?

Antibody-dependent cellular cytotoxicity (ADCC)

What causes the granuloma to form in tuberculosis infection and tuberculin reactions?

Activated M1 macrophages kill intracellular bacteria as part of the Th1 response, causing the granuloma to form.

How do CD8+ (cytotoxic T cells) kill microbes?

Granules: perforins, granzymes

TNF-beta: directly toxic to some tumor cells

FAS-FAS ligand complex: causes apoptosis

What are the two killing pathways of cytotoxic T cells?

Intrinsic (perforin) and extrinsic (CD95 or FAS/FASL)

How do CD8+ T cells recognize endogenous antigen?

Using MHC class I

What is the prime example of an INNATE cytotoxic cell?

Natural Killer cells

What do natural killer cells attack?

Cells lacking MHC class I (missing self)

Antibody-coated cells (antibody-dependent cellular cytotoxicity)

Stressed cells

Natural Killer cells produce what cytokine to activate macrophages?

Interferon gamma