last of immune material

Humoral immunity

macrophages, found in “humors,” antibodies, complement

Exclusively mean antibodies!

If you filter cells out, what is left is humoral immunity

Opsonions, antitoxins, hemolysis, Ab, bacteriolysis

Abs involved in

Neutralization, opsonization, complement activation

B cells must be activated (2 ways)

• Thymus dependent

• Thymus independent

Thymus independant

1. polyvalent antigen binds BCR → P1-3 kinase → ras/Mapk

2. LPS +TLR → MyD88, Ikky

Thymus dependent

1. Antigen binds BCR and/or C3b → PI 3 kinase → Ras/MapK

2. MHC 2 → Th binds → Nik/p100

Thymus independent antigens activate B cells w/o T cell help

T1 antigens activate TLR and BCR → not species specific → general Ab

TLR and BCR bind to same antigen

TI-2 antigens

• need to be polymers

• crocs-like BCRs

• Must be mature B cells

  • don’t do affinity maturation but can do low levels of class switching

Activated DCs release a cytokine BAFF

Aumugents production of Ab against TI-2 antigens and induces class-switching

What are the benefits of thymus-independent activation?

Quick, great for encapsulated bacteria (TI-2)

Many species can be targeted

Not very specific/strong

Thymus indepdendant antigens and linked recognition

Specific T cells are activated by antigens that may reside within viral particle. B cells recognizes surface epitope of a virus can process and presented other antigen epitopes

→ Virus-specfic Tfh provides help B cels that recognize linked epitope

Linked recognition

When the activating T cells recognize the same antigens as the B cell

STRONGEST MOST ROBUST IMMUNE RESPONSE

• same antigen, not same epitope(part) of antigen

Linked recognition should prevent most autoimmunity

Requires BCR binding of antigen → presentation of right peptide

TCR binding right peptide-mhc complex

Linked recognition and Hapten carrier effect

Hapten: small molecules that are non-immunogenic alone but when attached to carrier protein becomes immunogenicity (make look foreign-non self)

Multiple haptens on same carrier can crosslink BCRs→ b cells generate Abs against happen while t-cells recognize peptides from carrier protein phagocytosis (will digest and present)

How do we get B cells and T cells to encounter e/o

Location

• T cell and B cell rich areas are close to each other

Once activated, lymphocytes move to the same area to allow interaction

1. Before activation, resting B cells express CXCR5 and reside in follicles and T cells express CCR7 and reside in T-cell zones

2. Activated B cells induce CCR7 and EB12, and T cells induce CXCCR5 , and both cells migrate to follicular and inter follicular regions (highest concentration of both chemokines, higher changes of finding partner)

3. Interactions with T cells sustain EBI2 expression on B cells which move to outer follicular and inter follicular regions

4. Some B cells migrate to form a primary focus and different into plasma blasts while some T cells induce Bcl-6 and become Tfh (stay in B cell follicle and make Ab)

Antigens can also be presented on macrophages

Opsonized antigens recognized by complement receptors on macrophages

• present antigen to B cells

• ALso moves antigen to follicular dendritic cell

T cell/B cell interaction stabilized by SLAM proteins

SLAM: signaling lymphocyte activation molecules

• maintain binding

  • homotypic binding

  • propagates signa;

SAP; changes affinity, lack of SAP prevents adhesion of naive T cells to B cells

Once activated, some B cells become primary focus

Recive signal and proliferate signals

Move to lymph nodes

Move to area between T cells and red pulp (spleen)→ divide rapidly and differentiate

Plasma cell

Only release Ab

Resting B cell and plasma blast

Form germinal centers

• found in follicles

B cells and Tfh

Form dark and light zone

later than primary focus and lasts longer

Dark zone

High proliferation and density

Mostly B cells called centroblasts

Decreased BCR expression

• cells can move between zones - cyclic re-entry

Light zone

Can encounter FDC and Tfh

B called called centrocytes

Increased BCR expression

• cells can move between zones - cyclic re-entry

Somatic hypermutation

Increase mutation rate of V-region Ab

IF favorable, passed on → if not, B cell dies

Mut introduced through AID

• clones w better Ab affinity are selected for

Activation induced cytidine deaminase (AID)

Deaminated C → U

Must be ssdna so has to access based to unwind

can make any mutation

Must happen in dark zone

B cells compete w other clonal B cells → light zone and encounter FDCs and Thf

If higher affinity, more likely to receive survival signals → re-enter dark zone for further mutation → differentiate into Ab-generating plasma cells

Cyclic re-entry helps select for higher affinity

Somatic hypermutation v. affinity maturation

SHM: increases mut rate (genetics)

AM: increases Ab affinity for antigen (protein)

AM= SHM + cyclic re-entry selection

B cells make

IgM, IgD, IgG, IgE, IgA

Different in constant regions, have different roles of Ab

IgM

Made first

some IgD through alt. splicing

Made from same mRNA transcript

Alternative splicing

How membrane-bound v. secreted versions are made

Dif carboy terminus

Class-switching

Can’t go back from!

In front of every C-region we have a switch, activated by upstream promoter

AID only works on ssDNA

• Transcription needs to happen for ssDNA to form

• Controlled by regulating transcription → done by cytokines

• AID, UNG, APE1 introduce clustered nicks on dsDNA

How is AID only guided to these regions

Switch regions G-rich

Form R loops that stall RNAP

Recruits AID only there

The Ig formed will depend on which switch sites are simultaneously transcribed

IgM and IgA are polymeric

IgM pentameric

IgA dimeric

1. IgM

Made first, pentamer is larger

• mostly found in blood - heart

• main purpose is to protect from BLOOD INFECTIONS

• lowest affinity, highest avidity

• 5 chains w 2 binding sites

• When binds, CLAWS

IgD

Made after IgM

found at low levels, mostly membrane bound

no obvious phenotype

IgA

Dimer

Important for mucusal immunity

Protection of epithelial tissues (gut, respiratory tract, tear, salivary gland)

high in breast milk

Move accros epithelial membranes

no phagocytes or immune cells in gut so IgA made job is neutralization

IgE

Binds constant region first

Strongly binds to mast cells

• Fc receptor

• Upon antigen binding, signals release granule content (histamines) - degranulates

• Mostly beneath epithelial tissue

IgG

Main form in blood and extracellular fluid

75% of Ab in serum- many isoforms

Can be transported across placenta - protects fetus w maternal Ab

IgG4: great for for neutralization while not being pro-inflammatory, good for pathogens you haven’t encountered

Neutralizing Antibodies

Bind and neutralize toxins, pathogens

Many pathogenic bacteria secrete toxins

• Molecules that kill cells

• Mainly proteins

Toxins create ideal environment

Nutrient release from dead cells

Kill/change immune cells

Many toxins have protein chains connected

Piece 1: Binds receptors on target cell and drives endocytosis

Piece 2: Poisons cells many ways

Ab block receptor binding to toxin!

Virus-neutralizing antibodies work similarly

Virus binds to receptors on cell surface → receptor mediated endocytosis of virus

-acidification of endoscope after encoytsosis triggers fusion of virus w/cell and entry of viral DNA

• Ab blocks binding to virus receptor and can also block fusion event

• will coat virus in Ab, virus can’t access receotit to internalize

Neutralizing Ab and bacteria

some bacteria grow inside the cell

Ab neutralize very similiar as toxins/viruses

1. colonization of cell surface by bacteria that bind via bacterial adhesions

2. some bacteria some internalized and propagate in internal vesicles

3. Abs against adhesins block colonization and uptake

Bacteria that grow extracellularly

Ab can neutralize membrane proteins (adhesins/secretion)

Bacteria can’t stick to our cells or inject toxins

Beyond neutralization

Specific ab '

Bacterial toxins → neutralization

Extracellular bacteria → opsinization

Bacteria in plasma→ complement activation

Ab constant region recognized by Fc receptors

• Each Ab has different Fc region

• Diff cell types recognize this region

• Recognition through Fc receptors -bind diff classes

Fc receptor types

Phagocytes recognize and bind antigen

Many Fc receptors

IgE high affinity

Why would B cells have Fc receptors??

Feedback inhibition

B cell won’t develop - have enough Ab

Fc receptors play keep role In phagocytosis

AB variable region binds target

Fc receptors vind Ab

Multiple AB in region crosslink Fc receptors leading to signal activation

• prevents signaling by free Ab

Activated macrophage willl phagocytosis

Fc receptors play key role on NK killing virus-infected cells

Ab-dependant cell-mediated cytotoxicity

Ab binds antigen on surface of target cells → Fc receptors on NK cells recognize bound Ab → crosslonking of Fc receptors signals Nk cell to kill target cell

What antigens involved in ADCC

Viral proteins expressed on surface

Tumor-associate antigens → recognizes by Ab then recognized by NK

Can’t phagocytose large multicellular organisms

Abs will bind organism → Fc receptors bind → releases toxic granules and activate ADCC

Under normal condutions, AB and Fc receptor not interaction

Mast cells bind IgE before IgE binds antigen

VERY VERY high affinity

Most IgE be bound to mast cells

• not free

Activated upon binding multivalent antigens

• need to be cross linked

Release tons of signaling molecules - including histamines

Both innate and adaptive immunity are important for effective clearance

• Mild infections can be cleared by innate alone

• adaptive responses require innate immunity (for antigen pres)

• Ideally completely clear pathogen

  • if not, chronic/reccurent infection

Only specific parts of the immune system are activated upon infection

Activating all immune cells is wasteful, damaging, not tailored for pathogen

To solve this: sense what type of pathogen is present and where, only activate WHAT IS NEEDED AND WHERE ITS NEEDED

Type 1 Immunity

Intracellular bacteria, viruses, protozoa

Leads to IgG production through IL-12

Type 2 immunity

Parasitic worms, venom, allergies

• almost always on for wound healing

Type 3 immunity

Extracellular bacteria, fungi

PAMP-sesing activates diff responses

Which response depends on

• what PAMPS are recognize

• where they are

• which cytokines are produced

Type 1 response is induced by IL-12

Created by macrophages and DCs ( also lil bit of monocytes and neutrophils)

Can be induced by

• LPS

• Protozoa

• Viral DNA - endosomal TLRS**

• Intracelular PAMPS/Prrs

Leads to IL-12 release

IL-12 drives IFN-y production, NK activation, Th1 differentiation

Sends signal to bone marrrow- to make immune cells

In type 1, CD8 T cells can be activated two ways

DCs expressing high levels of B7 as a result of infection can activate naive CD8 T cells → Pathogen-specfic CD8 effector cells expand and become cytotoxic

Cytokines IL12 and IL18 made by DCs ca induce bystander CD8 T cells to produce IFN-y → IFN-y produced by bystander CD8 T cells can activate macrophages and other cells to promote general resistance to bacteria and viruses

IFN-y acts are positive feedback in type 1

Th1 secretes IFN-y

IFN-y activates macrophages/nk cells

IFN-y drives Th1 differentiaition

Also increase Il12 release

Ensures robust response

Innate lymphoid cell 1 plays a signaling role in type 1 immunity

ILC1

Main role: IFN-y secretion

Th1 cells play multiple roles in type 1 (Macrophage-focused)

Produce IFN-y and CD40L which induce and activate m1 macrophages → enhances macrophage killing of engulfed bacteria

Fas ligand and Lt-beta produced by Th1 cells induce apoptosis of bacteria-laden macrophages → kills chronically infected cells, releasing bacteria to be destroyed by fresh macrophages

IL-2 produced acts on CD4+8 cells - > alters balance of Th1 and Tfh differentiation to favor Th1 and expansion of CD8

Il3 and GM-CSF produced by Th1 stimulate production of monocytes in bone marrow→ induces monocytes differentiation in the bone marrow

Th1 cells produce TNF-alpha and LT-alpha which act on local blood vessels → activates endothelium to induce macrophage binding and exist blood vessel at site of infection

CCL1 induced is a chemoattractant for monocytes→ causes macrophages to accumulate at site of infection

Failure of type 1- myobacteria infections

For viruses- nk cell activation, CD8 T cell activation, enhancement of B cells activation, class switching to IgG

IFN stimulated genes (ISG)

• restrict viral replication

• won’t discuss protozoa

Type 2 immunity focuses

on multicellular parasites

Main cause of allegergues (pollinosis)

What triggers type 2 immunity

DAMPS (damage associated molecular patterns)

associated w tissue DAMAGE

For type 2 immunity, epithelial damage from helminth

• can’t be triggered sterilely

Epithelial damage can trigger ILC2 secretion of

IL-4 and IL-13 (and DC activation)

Tuft cells

Express taste receptors, found in gut and trachea, secrete IL-25 to activate ILC-2

Poor understood

IL-4 induces Th2 differentiation

Produced by eosinophils, basophils, mast, and Th2 cells

Inhibits Th1 differentiation

• prevents activation of type 1

many more cytokines involved

Th2 play a key role in helminth expulsion

Th2 cells produce IL-13 which induces epithelial cell repair and mucus → increased cell turnover and movement helps shedding of parasitized epithelial cells. Mucus prevents adherence and accelerates loss of parasite

IL-13 produced by Th2 cells increases smooth muscle contractility enhances work explosion → increased contractility of mucosal smooth muscle enhances warm expulsion

Th2 cells recruit and activate M2 macrophages via IL4 and Il13 → products of arginose-1 expressed by M2 macrophages increase smooth muscle contraction and enhance tissue remodeling and repair

IL-5 produced Th2 cells recruits and activates eosinophils → eosinophils produce MBP which kills parasites. They also mediate ADCC using parasite-specific Ig

Th2 cells drive mast cell recruitment via IL-3, IL-9. Specific IgE arms mast cells against helminths → Mast cells produced mediators such as histamine, TNF-alpha and MMCP. These recruit inflammatory cells and remodel the mucosa

Type 2 leads to M2 macrophages

M2 is focused on

• tissue repair

• fighting helminths

DAMPS= damage= need repair

IL-4 induces this

So type 1- M1

Type 2- M2

Arginase-1

Generates ornithine & polyamides

• not used for oxidative burst

Used for type 1 immunity

• aids in epithelial repair

M2 macrophages express Arg-1

M1 macrophages express Arg-2

Arg1 products trap helminth larva

Type 2 leads to IgE production

IL-4 released by Th2

Il-4 induces class switching to IgE

Antibodies help localize cytotoxic cells to them helminth organic,

Macrophages and neutrophils → no phagocytosis

Eosinophils → can’t do phagocytosis. increased inflammation, will de-granulate

For extracellular bacteria and fungi, type 3 immunity is induced

Activated by TLRs sensing

• flagellin

• fungal cell wall components

• PAMPs outside the cell- EXTRACELLULAR PAMP

Requires other inflammation signals

• prevents attach of microbiome

• caused by epithelial damage

Mediated Th17 cells

IL6 and IL23 play a key role in Th17 differentiation

ILC-3 synthesize IL-1B and IL-23

Trigger Il-6 and Il-23 release by APC’s (mainly DC)

Th17 found mainly at intestinal Barriers

• some suppress Treg 17

Th17 release IL-17A and IL-17F

IL-17 is a large family

• similar structure

• similar-ish function

• IL17f is of interest- highly and consistently expressed in asthma

Th17 plays multiple roles in responding to extracceular bacteria/ fungi

IL-17 and IL-22 produced by Th17 cells induce the production of antimicrobial peptides by epithelial cells → direct killing or growth inhibition of bacteria attached to the epithelium

IL-22 increased epithelial cell turnover → increased epithelial cell devision and shedding impairs bacterial colonization

IL-17 produced by Th17 cells activate stromal cells and myeloid cells to predict G-CSG which stimulates neutrophil production in bone marrow → increases circulating neutrophils to sustain supply of short-lived innate effectors at infection site

Il-17 produced by th17 cells activate stratal cells and epithelial cells to predict chemokines that recruit neutrophils → recruiment of neutrophils to the site of infection

CCL20 predicted by th17 is a chemoattract for other th17 → increased recruitment of th17 cells to site of infection

Th17 can differentiate into Th1 cells

Th17 is changeable

In the presence of il-12 can become Th1

Reg T cells can become either th17 or th1

Clonal contraction removes all unneeded effector cells

B and T cells are now unnecessary

Die to ways -

• death by neglect- no survival signals

• extrinsic apoptosis

dress up resources but a small number remain

Exhausted immune cells

cells that receive extremely high activation signals or have been activated for a long time start behaving differently

• including different cd markers

don’t perform their functions anymore

Cells might become exhausted while we still need them

• common w cancers

• infection not cleared d

Generation of immunological memory

quick generation of a response to an spreading encountered antigen

Ab show no significant decline and T-memory shows half life of 8-15 yrs

Primary, secondary of tertiary

Immune response based on number of times antigen is encountered

For B cells, later exposures can have class-switching, somatic hypermutation/affinity maturation

Depends on where memory B- developed

• germinal center v other

Multiple exposures lead

to more IgG vs IgM and higher affinity

Memory B cells have higher levels of MHC2 and B71 than naive B cells

Activated easier.faster

Memory T cells are distinct from naive and effector T cells

• low granule/effector molecule formation

• district tissue migration

• higher survival signals - dont need constant survival signals like effector cells

3-types of memory T cells

Central memory (Tcm)

Effector memory (Tem_)

Tissue-resident memory (Trm)

Central memory

migratory

blood → sedentary lymph organ → lymph→ blood (naive T cells)

Effector memory

Migratoyr

blood→ peripheral tissues → lymph system → blood

localize to inflamed tissues

Tissue-resident memory

Non-migratory

found in tissues

Secondary responses appear to be mostly memory cells

Memory cells become activated quicker than naive cells (never have a chance to turn on)

• if fails, naive will turn on

Upon memory cell activation, naive activation appears to be suppressed