Basic Immunology as it

Relates to AllergyDavid Sloane, MD

Allergy and ImmunologyBrigham and Women’s Hospital

NESA5 April, 2013

Disclosures

• (Genentech + Novartis) Unbranded Educational Talks on Asthma

• Contributor to the Mathematics Consortium Working Group

Objectives

• 1) To review the biology of cells, antibodies, and mediator molecules in healthy immunity and dys-immunity germane to allergy.

• 2) To explore the rationale for therapeutic agents such as omalizumab in the treatment of allergic diseases

• 3) Participants will develop the skills needed to educate patients about those aspects of the immune system relevant to the patient's allergic or immunologic disease and its treatment

Teleology• Two theories of the purpose of the immune

system:– (1) Defense against microbes (Janeway)– (2) Defense against danger (Matzinger)

What do you think the difference is between these two theories?

Immune System as a Matter Processing Network

Inside Outside

Safe

Dangerous

Reality Check

The Whole Megilah: Allergic Reaction System

Slide courtesy of Dr. Tse Wen Chang

Components of the System• Cells:

– Dendritic Cells and other “professional APCs”– T cells– B cells– Mast cells (and Basophils?)– Eosinophils

• Antibodies: What are they? What are they good for?– IgE– IgG4

• Mediator Molecules: What are they? What are they good for?– Interleukin (IL)-4– IL-13 – Thymic Stromal Lymphopoetin (TSLP)

Processing Stuff

Microbe

Antigen Presenting Cell (APC){DC}

Processing Stuff

APCT cell

The Whole Megilah: A closer view

IL4, TSLP

Wait a Minute!

• Why is this happening?• Do the two theories of the purpose of the

immune system help you?• What is the hygiene hypothesis?

Antibodies: The Immune System’s Attacks Dogs

From Janeway et al. Immunobiology V. 2001.

Antibodies: The Various Species or Isotypes

From Janeway et al. Immunobiology V. 2001.

The Role of IgE in Allergic Inflammation

• Necessary but not sufficient factor for *antigenic* stimulation of mast cells and basophils.

• Prausnitz (grass) and Küstner (fish) 1920s.• Reagin identified as IgE in mid 1960s.

IgE: Structure

• Molecular Weight ≈ 190,000 kD• Monomeric, two identical heavy chains, two

identical light chains ( or )

IgE: Synthesis

• B cells that undergo the isotype switch to C produce IgE

• Help from Th2 cells that express – a) CD40L and – b) IL-4, IL-13, TSLP

IgE: Circulation

• IgE circulates in the blood with a t½= 2-4 days (serum!)

• Normal serum concentration = 0-0.002mg/mL (the lowest of all five isotypes)

• x IU = 2.4x ng/mL (E.g., 125 IU = 300ng/mL)

IgE in Blood and Tissues

• In the blood, IgE binds to Basophils through the high affinity receptor for IgE, FcRI.

• IgE crosses from blood space into the extracellular space

• It binds to Mast Cells through FcRI• FcRI is also expressed by monocytes,

eosinophils, dendritic cells in peripheral blood, and Langerhans’ cells in skin.

FcRI and FcRII• FcRI Structure:– One chain that binds the Fc portion of IgE– One chain with ITAM– Two chains, each with ITAM

• FcRII– CD23– Expressed on mature B cells, activated T cells,

macrophages, eosinophils, follicular dendritic cells, platelets

– C-type lectin– Antigen capture leading to processing and presentation to

enhance immune responses.

Mast Cells (and Basophils)IgE FcRI

Mast Cells

• Live in – mucosal layers (gut, lung)– submucosal layer– dermis

• Mediators– Preformed (histamine, tryptase)– Rapidly synthesized (PGD2, LTC4)

– Not so rapidly synthesized (cytokines)

Measurement of Total Serum IgE: Why bother?

Burrows B, Martinez FD, Halonen M, Barbee RA, and Cline MG. Association of Asthma with Serum IgE Levels and Skin-Test Reactivity to Allergens. NEJM 1989;320(5):271-277.

Mast Cells and IgEIgE

FcRI

Allergen

MediatorRelease

Mast cell granules

Wait a Minute!

• Where is IgE acting?• Where do we measure IgE?

So What?

How do we treat Allergic Inflammation?

• Avoid the allergenic trigger (“I can’t eat that”)• Antagonize the mast cell mediators (“Where’s

my antihistamine?”• Throw a monkey wrench into the response

system (The story of the yetzer ha’rah)• Try to teach the immune network not to

attack (“Stay….staaaaay…. Good dog!”)

The binding specificities of a therapeutic anti-IgEThe binding specificities of a therapeutic anti-IgE

Slide courtesy of Dr. Tse Wen Chang

3 IgE:3 anti-IgE the largest3 IgE:3 anti-IgE the largestSoluble and no immune complex Soluble and no immune complex problemsproblems

Could IgE:anti-IgE complexes be beneficial?Could IgE:anti-IgE complexes be beneficial?They may serve as antigen sweepers, blocking antigens to access They may serve as antigen sweepers, blocking antigens to access

receptors on inflammatory cellsreceptors on inflammatory cells. .

IgE:anti-IgE complexesIgE:anti-IgE complexes

TT1/21/2 : anti-IgE ca. 20 days, IgE 1-2 days, : anti-IgE ca. 20 days, IgE 1-2 days, IgE:anti-IgE ca. 20 daysIgE:anti-IgE ca. 20 days

Immune complexes accumulate rapidly.Immune complexes accumulate rapidly.

Slide courtesy of Dr. Tse Wen Chang

• FcFcRI density on basophils falls by 97% in 3 months. RI density on basophils falls by 97% in 3 months.

• FcFcRI on basophils decreases with a half life of about 3 days. RI on basophils decreases with a half life of about 3 days.

• FcFcRI on dendritic cells are decreased substantially in two weeks.RI on dendritic cells are decreased substantially in two weeks.

From MacGlashan DW et al., J. Immunol. 158:1438 (1997)

Down regulation of FcDown regulation of FcRI in patientsRI in patients

Slide courtesy of Dr. Tse Wen Chang

Down regulation of FcDown regulation of FcRI in patients (cont.)RI in patients (cont.)

From MacGlashan DW et al., J. Immunol. 158:1438 (1997)

Allergy Immunotherapy:teaching an old dog a new trick, or

teaching it not to do an old trick• Introduce allergen in a non-threatening

manner and context• Elicit an IL-10 response from Treg cells instead

of an IL-4 and TSLP response from Th2 cells.• Thus, lead B cells to make the isotype switch

to IgG4.

• IgG4 binds to mast cell inhibitory receptors and blocks activation.

Mast Cells post ImmunotherapyIgE

FcRI

Allergen

NOMediatorRelease

Mast cell granules

IgG4

FcRIIb

Question 1

• Which of the following cells is thought to be the primary effector cell in anaphylaxis?– A. Eosinophils– B. Basophils– C. CD8+ T cells– D. Mast cells– E. Th17 cells

Question 1

• Which of the following cells is thought to be the primary effector cell in anaphylaxis?– A. Eosinophils– B. Basophils– C. CD8+ T cells– D. Mast cells– E. Th17 cells

Question 2

• Which of the following cells promotes B cells to undergo an isotype switch to make IgE?– A. Th1 cells– B. Th2 cells– C. Th17 cells– D. Treg cells– E. NKT cells

Question 2

• Which of the following cells promotes B cells to undergo an isotype switch to make IgE?– A. Th1 cells– B. Th2 cells– C. Th17 cells– D. Treg cells– E. NKT cells

Question 3

• Fill in the blanks to make this statement correct: A major hypothesis on how allergy immunotherapy works is the belief that ____ promotes B cells to make ____.– A. IL-4.... IgE– B. IL-13.... IgA– C. IL-10.... IgG4– D. IL-18.... IgD– E. Fractalkine.... Thymic Stromal Lymphopoetin (TSLP)

Question 3

• Fill in the blanks to make this statement correct: A major hypothesis on how allergy immunotherapy works is the belief that ____ promotes B cells to make ____.– A. IL-4.... IgE– B. IL-13.... IgA– C. IL-10.... IgG4– D. IL-18.... IgD– E. Fractalkine.... Thymic Stromal Lymphopoetin (TSLP)