Hyper IgM Syndrome

CD40L deficiency (on X chromosome, X-linked).

Patients do not have IgG, IgA. IgG is needed for opsonize capsulated bacteria. These patients are susceptible to infection by encapsulated bacteria.They can make IgM through TI-antigens.

They also have defect in cell-mediated immunity, which involves T cell activation of M.They also suffer from opportunistic infections (bacteria, virus, fungi that normally do notcause disease).

Missing in patients

Class switch to IgG, IgAMutation (cannot happen in patients)

IgM (not affected)

Defects in B cell activationAnd germinal center formation.

Defect is in T cell.

Hyper-IgM Syndrome

Activation-Induced Deaminase (AID) DeficiencyUDG deficiency

Patients are susceptible to bacterial infection, but not opportunistic infection.They have normal T cell function. The defect is limited to B cells.

B cells are activated and germinal centers are formed. But no class switchingand somatic hypermutation take place.

V(D)J 3 1 2b 2a

Germline transcription Germline transcription AID

V(D)J 3 1 2b 2a

C U C UCleavage at U (UDG, etc)

Class switch recombination

C U

Somatic hypermutation

Immune Response to Extracellular Bacteria

Extracellular Bacteria, toxin

complement NeutrophilsMacrophages

Lysis

APCsDendritic cells

CD4 T cell

TH2

B cell

B cell activation

antibodies

Neutralization

Complementactivation

Opsonizationfor phagocytosis

phagocytosis

inflammation Humoral immunity

Complements, phagocytosis, and antibodiesare critical immune effector functions to extracellular bacteria and toxins.

Immune response to intracellular bacteria

bacteria

complement phagocytes

neutrophils macrophages

Killing of bacteriaIntracellular bacteria can Survive in macrophage

Neutrophils

High bactericidal activity

Short-lived

Intracellular bacteria cannot establishInfection within neutrophils

inflammation

macrophage

Bactericidal activityDepends on activation status

Long-lived

Intracellular bacteria can establishInfection within macrophage

Many intracellular bacteria interfere with phagosome maturation

Phagocytosis

phagosomeH+

Vacuolar ATPaseProton pump acidifiesphagosome

pH<5.5

ROIRNI

lysosome

Lysosomal enzymes

phagolysosome

Mycobacterim tuberculosis exclude proton pump.Produce NH4+ to neutralize pH.

M. Tuberculosis expresses iron binding proteins such as siderophore to obtain iron

Many intracellular bacteria produce superoxide dismutase and catalase that detoxify ROI.

M leprae produces ROI scavenger. S. enterica exclude NADPH oxidase from the Phagosomal membrane and interfere with the release of ROI into the phagosome.

Listeria monocytogenes (listeriosis)Produces cytolysin to escape into the cytosol

Immune response to intracellular bacteria

Mycobacterium leprae: Leprosy, macrophage, Schwan cells, Nasopharyngeal mucosa

Listeria monocytogenes: Listeriosis, macrophage, hepatocytes

Rickettsia rickettsii: Rocky Mountain Spotted fever, endothelial cells, blood (tick bite)

Rickettsia typhi: Typhus, endothelial cells, blood (flea bite)

Intracellular bacteria may also infect nonphagocytic cells through receptor-mediated entry.These cells have little anti-bacterial activities and serve as hapitat.

Intracellular bacteria is not accessible to antibodies.Effective immune response require activation of Macrophage and eliminate infected cells.

Activation to increaseAnti-bacteria activity

Cell death

Accessible to immune attack

Natural Killer (NK) cells

Hematopoietic stem cell(HSC)

Myeloid pregenitor

Granulocyte-monocyte progenitor

monocyte

Bone marrow

Neutrophil1-6% 50-70%

Blood

Lymphoid progenitor

B cell progenitor

B cell

T cell progenitor

T cell

thymus

Lymphocyte (20-40%)

macrophage

Tissue

NK cell

Large granular lymphocytes(LGL)

(5-10%lymphocyte)

NK cells produce interferon (IFN-), whichactivates anti-bacterial activity of M.

NK cells can be activated by cytokines produced by Macrophages and dendritic cells.

bacteria

Macrophages

Dendritic cells

IL-12IL-18TNF-

NK cells IFN-

IFN activates the production of ROI (NAPDH oxidase) and RNI (iNOS, inducible nitrogenOxide synthetase).

IFN stimulates antigen presentation by class I MHC.

Increases the expression of class I MHC

Increases the expression of PA28

Proteasome degrades ubiquitinated proteins.Ubiquitinated proteins

peptides

4 heptamerrings

cap

cap

The proteasome for antigen processing contains LMP2, LMP7, and LMP10.

Such proteasome preferentially cleaves peptide bonds after hydrophobic or basic residues.

Proteasome activating molecule (PA28) is inducible by interferon .

PA28 increases the release of cleaved peptides.

NK-T cells

Express both TCR and NK markers.

TCR is composed on unique chain (V14-J281) and three chains.

May recognize CD1-presented mycobacterial phospholipids.

T cells

May recognize phospho-ligands from mycobacteria.

The recognition does require MHC or CD1. May recognize the ligands directly.

NK-T cells and T cells can also produce IFN-.

Innate-like lymphocytes

bacteriaPhagocytosis

Degradationproduct

Endocytosismacropinocytosis

DCs present antigens to T cells.

Class I MHC-antigen

Class II MHC-antigen

Dendritic cells can present exogenousantigen on both class I and class II MHC.

Cross-priming

Abundant MHC and B7 for T cell activation

Activation of CD4 T cells

Naïve CD4 T cells Activated T cellsAg-DC Immature effector

T cells (TH0)

TH2 cells remain in secondary lymphoid tissues and facilitate B cell activation.TH2 cells secrete IL4, IL5, IL10, TGF-.

TH1 cells express move to sites of infection.

TH1 cells produce IFN-, IL2, which is crucial for activating macrophages.

The response is generally dominated by either TH1 or TH2.

Secondary lympoid tissues TH1

TH2

IL10 IFN-

IL12

IL4

During intracellular infection, the production of IL12 by DCs favor the differentiationof TH1 cells.

What favors the production of TH2 cells in humoral immune response?

Naïve T cells

Activated TH1 cells cease the production of L-selectinAnd stops homing to secondary lymphoid tissues.

Activated TH1 cells home to inflammation sites.

TH1 cells express new integrin VLA-4..VLA-4 binds to VCAM-1, which is induced in inflamed endothelial cells.The interaction initiates the extravation of TH1 cells into the infection site.

TH1 cells express increased levels of LFA-1 to interact with ICAM-1 on endothelial cells.

TH1 cells activate macrophage.

TH1 cells interact with the antigen-MHC II and provide activation signals

Similar to B cell activation:

IFN-

CD40L

IL4

Activated macrophage exhibit increased anti-bacterial activities.

Macrophages that are chronically infected with intracellular bacteria lose the abilityto be activated by IFN-.

TH1 cells express Fas ligand and TGF- that induce the apoptosis of these macrophages.The bacteria are released and phagocytose by new macrophages.

Activated TH1 cells secrete IL2, which facilitate the proliferation of effector T cells.

TH1 cells secrete IL3 and GM-CSF (granulocyte macrophage colony stimulatory factor),which induces the production of more neutrophils and monocytes in the bone marrow.

TH1 cells secrete TNF- and TNF-which induce inflammation in the bood vessel to recruit more phagocytes. TH1 cells secrete CCL2 to facilitate the chemotaxis of macrophage to the site of Infection.

TH1 cells induce the apoptosis of chronically infected macrophages

TH1 cell is the central coordinator of immune response to intracellular infection.

The activation of CD8 T cells produce cytotoxic TLymphocytes (CTL).

Bacteria (L. monocytogenes) can produce cytolysins to escape into the cytosol.

Bacteria (L. monocytogenes) can also enter into nonphagocytic cells (hepatocytes), and reside in the cytoplasm.

Some phagosomal bacteria (S. enterica) possess a specific secretion apparatus that translocatesproteins into the cytosol of host cells.

Antigens from bacteria that persist in the phagosome may leak into the cytosolic compartment.

Bacteria induce apoptosis of host cells. These result in the formation of vesicles Containing antigenic cargo that can be shuttled to dendritic cells for cross-priming.

In general, the bacteria that stay in the cytosol are the most potent stimulators of CD8 T cellresponse, while those in phagosomes are primarily dependent on CD4 T cell/Macrophage activation.

CD8 T cells are activated by antigens derived from the cytoplasm in the context of class I MHC.

Activation of CD8 T cells

The most important activators of CD8 T cells are DCs.Activation of CD8 T cells require more co-stimulatory activities than CD4 T cells.

TH1 cells facilitate the activation of CD8 T cellsby secreting IL2.

Activated CD8 T cells (CTL) home to inflammation sites.

CTL turns of the expression of L-selectin.CTL expresses VLA-4 and increased level of LFA-1.

CTL kills infected cells.Conjugate formation

Recognition of antigenBy TCR activates LFA-1to form more stableInteraction with ICAM.

TCR-Ag/MHC-CD8Interaction also stabilizeThe interaction.

Activated CD8 T cells interact with target cellswithout the need of B7 constimulatory signal.

CTL reorients its cytoskeleton.

The clustering of TCR signalsthe reorientation of the cytoskeleton and focus therelease of effector moleculesat the site of contact with the target cell.

Greencytoskeleton

RedLytic granules

Outer ring (red): LFA-1:ICAM

Inner ring (green): TCR-coreceptor-Ag:MHC

Immunological synapse

Similar immunological synapse forms betweenTH2 cells and B cells during B cell activation.

The formation of immunological synapse ensures delivery of effector molecules to target cells without affecting bystanders.

It also ensures high local concentration of the effector molecules.

CTL releases cytotoxins from lytic granules.(T cell-mediated cytotoxicity)

Perforin polymerizes in target-cell membranes to form transmembrane pores.

The pore can cause lysis and facilitate the entry of other cytotoxins into target cell.

Granzymes induce apoptosis of target cells.

Caspase-activatedDeoxyribonuclease(CAD) Fragmentation of nuclear DNA

Perforin releases granzyme B from Endosome vesicles

tBid induces the release cytochrome C

Granzyme B and caspase also cleaves Bid to tBid.

Granzyme B Cleaves and Activate caspase 8

Perforin pore facilitatesThe entry of granzymes

Fas ligand (CTL, TH1) induces apoptosis.

FasL is a TNFFamily of membraneassociated cytokines.

(TNF-a, CD40L)

Fas is a TNFRFamily memberTNF-R, CD40

FADD is an Adaptor protein

Clustered pro-caspase 8 Transactivate by proteolytic cleavage.

Granulysin has potent bactericidal activity.

Granulysin may be critical for the killing mycobacteria.Perforin may facilitate the entry of the protein into phagosomal bacteria.

Why aren’t CTL killed?Protective membrane proteins binds to perforin or prevent pore formation?

May disrupt membranes.

CTL also secretes IFN-to activate Macrophage.

The apoptosis of infected cells release intracellular bacteria to be eliminated by other immune functions.

Immune response to intracellular bacteria lead to the formation of granuloma.

BacteriaComplementMast cellsMacrophagesDCs

inflammation

Macrophages

CD8 T cell activation

CD4 T cell activation Th1

CTL

Activated macrophage kill bacteria within the granuloma.

Encapsulation by fibrosis (promoted by TNF) and calcification.Necrosis (promoted by TNF) leading to reduced nutrient and oxygen supply.The granuloma contains the infection.

Frequently, bacteria are not completely eradicated. They enter into a dormant form.

NK, NK-T, T cells

Neutrophils

granuloma

The predominant cellis macrophage.

MP can be inactivated by bacterial components. Some of these factors can Induce the maturation of immature monocytes into epithelioid cells and multinucleatedGiant cells.

Mycobacterium leprae (leprosy)

Lepromatous leprosy: TH2 response (IL4, IL5, IL10)Cell-mediated immunity is depressed and M. leprae infected cells are abundant. Bacteria are widely disseminated.

Tuberculoid leprosy:TH1 response (IL2, IFN-, TNF)Cell-mediated immunity with macrophage activation controls the infection. Infection is contained within granuloma with local damage.

TH1 mediated immune response is critical for controlling intracellular bacteria.

Relevant parts in book

CTL: page 319-329

Chronic inflammation: page 352

TH1/TH2: page 288-291