The Immune System and Allergy

William L. Houser, Jr., M.D.

Overview of Human Immunity

Innate Immunity

• Barrier defenseSkinMucous membranesSecretions

• Internal defensesPhagocytic cellsAntimicrobial proteinsInflammatory responseNatural Killer (NK) cellsComplement

Adaptive (Acquired) Immunity

• Humoral responseAntibodies

In body fluids

• Cell-mediated responseLymphocytes (cells)

In body cells

Acquired ImmunityAntigen detection by B lymphocyte

• B cell receptors

2 heavy and 2 light chains

Antigen binding site

Acquired Immunity Antigen detection by T lymphocyte

• T cell receptorAlpha chain and Beta chain

Bind only to antigens presented to T cells by a host protein produced by genes from the MHC

B and T cell Interaction

• Antigen presenting cell (dendritic cells, macrophages, and B cells) interact with T helper cell

• Activated T cell binds to B cell

• Activated B cells become plasma or memory B cells

• Secreted antibody from

plasma cells

Antibodies

• Differ from B cell receptors only in the constant (C) region of the heavy chain

• The five major types of heavy chain constant regions determine the five major classes of antibodies (M, G, A, E, and D)

• Changes in the heavy chain gene that switch B cells from producing one antibody class to another occur only in response to antigen stimulation and specific regulatory signals from T cells (cytokines cause isotype switching)

Allergy

• An exaggerated immune response to certain antigens (allergens)

• Overproduction of IgE antibody specific to the allergen

• IgE binds to mast cells in the connective tissue of certain organs like the skin, nose, eyes, and lung.

• Recontact with the allergen binds the IgE on the mast cell and cause cells to degranulate releasing histamine and other mediators

Example of an Allergic Response

Why do people become allergic?

Contact with Allergens

Conditions caused by Allergy

• Anaphylaxis – whole body, more than 1 organ system, life threatening

Caused by bee venom, foods including peanuts, tree nuts, and seafood, and medications

Treated with epinephrine (EpiPen)

Conditions caused by Allergy

• Allergic rhinitis (nose) – sneezing, runny nose, stuffiness, itching

• Allergic conjunctivitis (eye) – watery, red, itching

Perennial – dust mite, mold, animal dander

Seasonal – mold, pollen (tree, grass, weed)

Conditions caused by Allergy

• Asthma – an inflammatory condition of the lung caused by allergy 60-85% of the time

Cough, wheezing, shortness of breath

Triggers – see below

Other Allergy Conditions

• Food allergy – can cause skin (eczema or hives), gastrointestinal, or systemic symptoms (anaphylaxis)

Other Allergy Condtions

• Bee venom allergy

• Drug allergy

• Latex allergy

• Contact allergy – nickel

• Skin allergy – eczema or urticaria (hives)

Eczema

Urticaria (Hives)

Diagnosis of Allergy

• History – type of symptoms, timing and duration, family history, past history

• Physical examination

• Testing – Skin testing– RAST or ImmunoCap (blood)

Skin Testing

Skin Testing

Allergy Treatment

• Allergen Avoidance

• Medication

• Allergen Immunotherapy (Allergy Shots)

Allergen Avoidance

• Dust mites – bedding encasings, furnace filters, air cleaners, remove feather/down, remove stuffed animals

• Animals – remove

• Mold – clean, reduce humidity

Medication

• Antihistamine

• Decongestants

• Inhalers

• EpiPen

New epinephrine injectors

• Auvi - Q

Allergen Immunotherapy

• SCIT – subcutaneous (shot)

• SLIT – sublingual (drops under tongue)

Questions