Veterinary Immunology

1. Veterinary Immunology Type I Hypersensitivity Dr. Chi-Young Wang

2. Generally IgA and IgG production • Atopy: Excessive production of IgE • Affected Individuals: Atopic • Atopic dermatitis: Terries • Parasitic worms and insects: IgE

3. Immunoglobulin E: 200 kDa • Half life: Two days • IgE bound to Fcε receptors on mast cells and then its half life was 11 to 12 days

4. IL-4, IL-5 or IL-13 produced by Th2 cells from atopic individuals • IgE synthesis stimulated by CD40, IL-4, IL-5 or IL-13 • IL-4 produced by stimulated mast cells

6. The FcεRI (αγ2) is found on dendritic cells and monocytes. Antigen binds to IgE and the complex binds to this receptor. It is served as exogenous antigens. The expression of FcεRI (αγ2) is enhanced by IL-4 from Th2 cells.

7. IgE receptors: high-affinity: FcεRI low-affinity: FcεRII • FcεRI- αβγ2 or αγ2 FcεRII- selectin-binds to complement receptor CR2 • The affinity of FcεRI for IgE was very high (10-10 M)

9. Activation

10. Connective tissue and skin mast cells are rich in histamine and heparin, whereas intestinal mast cells contain chondrotin sulfate and little histamine • Connective tissue mast cells remain at constant levels but mucosal mast cells can proliferate and mucosal mast cells respond specifically to invasion by parasitic worm

11. Many different stimuli can trigger mast cell degranulation • IgE and antigen together can trigger mast cell degranulation and generate allergic diseases • Allergies are but a special type of inflammation • Cytokines, chemokines, chemical agents, physical stimuli, insect venoms, viruses can activate mast cells • Defesins, anaphylatoxins, neuropeptides, adenosine, and endothelins can trigger mast cell degranulation

12. Mast cells express diverse pattern-recognition receptors (PRRs) that permit them to recognize pathogens • These include TLR1, TLR2, TLR3, TLR4, TLR6, TLR7, TLR9, and a mannose receptor (CD48) • Bacterial peptidoglycans acting through TLR2 stimulate histamine release, whereas lipopolysaccharides acting through TLR4 do not

13. The triggering of rapid exocytosis by an antigen molecule cross-linked two FcεRI→activation of tyrosine kinase →phospholipase C →diacylglycerol and inositol triphosphate →increase intracellular calcium →activation of protein kinase →phosphorylation of myosin →secretory lysosomes • Activation of phospholipase A →arachidonic acid to form leukotrienes and protaglandins

16. Mast cells secrete histamine, serotonin, prostaglandin, leukotrienes, chitinases, and CCL3 • These cytokines are proinflammatory or promote Th2 responses, or both • Mast cells also release heparin-containing granules; they are rich in TNF-α • The presence of heparin stabilizes the TNF-α for a long time

17. IL-33, a member of the IL-1 family, plays a role in inflammation and promote Th2 responses • IL-33 is produced by smooth muscle cells, epithelial cells, fibroblast keratinocytes, dendritic cells, and activated macrophages • IL-33 binds to a receptor on mast cells, basophils, and Th2 cells • When bound to mast cells, it induces their degranulation and triggers acute anaphlaxis in the absence of antigen • IL-33 can not mediate this degranulation alone, The mast cells must be sensitized by prior exposure to IgE

18. α，β adrenoceptors for catecholamines • Norepinephrine and phenylephrine →stimulate α adrenoceptors Propanolol →block β adrenoceptors THESE LEAD TO MUSCLE RELAX • β receptor stimulation and α receptor blockage →inhibition of mast cell degranulation

19. Antigen is injected into the skin and Immediate acute inflammatory response is triggered: within 10 to 20 minutes; caused by mast cell degranulation • Late-phase response: peak at 6-12 hours; redness, edema, and pruritus; mediated by eosinophils and neutrophils

20. Eosinophils are attracted to sites of mast cell degranulation • A half lfe-12 days. Parasites increase eosinophils -2% in dogs and 10% in cattles • Primary and small granules contain acrylsulfatase, peroxidase, and acid phosphatase • Large crystalloid granules have a core of major basic protein (MBP); eosinophil cationic protein; eosinophil peroxidase (EPO) ; eosinophil-derived neurotoxin

23. Eosinophil Activation • Th2 cells and mast cells produce IL-5 (eotaxins) which stimulate the release of eosinophil • Eotaxins, histamine, imidazoleacetic acid, leukotriene B4, 5-hydroxytryptamine (5-HT), and platelet-activating factor (PAF) attract eosinophils to the sites • Allergens activate eosinophils, stimulates their chemotaxis, and up-regulate CR3 expression

24. Eosinophil Activation →enter sites of mast cell granulation • The sum effect of eosinophil activation is to kill the parasites and the major function of IgE-mediated responses is the control of helminth parasites • Activate eosinophils express MHC II molecules and serve as antigen-presenting cells and also express the immunosuppressive enzyme (IDO) to promote Th2 responses

25. Eosinophil Degranulation and Mediators • The sum effect of eosinophil activation is to kill the parasites and the major function of IgE-mediated responses is the control of helminth parasites • Activate eosinophils express MHC II molecules and serve as antigen-presenting cells and also express the immunosuppressive enzyme (IDO) to promote Th2 responses

26. Eosinophil Degranulation and Mediators • Eosinophil undergo piecemeal degranulation. This degranulation occurs in response to IgE-coated parasites, antigen-bound igE, many chemokines, PAF, and C5a • Eosinophil granules contain cationic proteins, peroxidase, and MBP. It also produces leukotrienes and PAF. Partcles bound to eosinophil receptors lead to a respiratory burst (OBr-)

27. Eosinophil Degranulation and Mediators • Eosinophils also synthesize and secrete IL-1α, IL-3, IL-4, IL-5, IL-6, granulocyte-macrophage colony stimulating factor (GM-CSF), TNF-α, transforming growth factor-α (TGF-α), and TGF-β • Eosinophils produce CCL5 and CCL11 which attract more eosinophil • Eosinophil-MBP activates mast cells to release histamine, IL-3, IL-5, and GM-CSF, all of which promote eosinophil degranulation, growth, and survival

29. Allergic Anaphylaxis • A severe, life-threatening generalized or systemic hypersenitivity reaction (triggered by histamine and serotonin) • Horses: the lung and the intestine are major organs; bronchial and bronchiolar constriction leads to coughing, dyspnnea, apnea, and diarrhea • On necropsy, severe pulmonary emphysema, peribronchiolar edema, and edematous hemorrhagic enterocolitis

30. Allergic Anaphylaxis • Cattles: characterized by profound systemic hypotension and pulmonary hypertension • Pulmonary edema and severe dyapnea due to the constriction of the pulmonary vein • Uriation, defecation, and bloating caused by the contraction of smooth muscle of the bladder and intestine • The main mediators: serotonin, kinins, and leukotrienes

31. Allergic Anaphylaxis • Because of the anticoagulant properties of heparin from mast cells, blood of cattle may fail to coagulate • Dogs: liver is the major shock organ, specifically the hepatic vein • Initial excitement followed by vomiting, defecation, and urination • The dogs collapses with muscle weakness and depressed respiration, becomes comatose, convulses, and dies within an hour

32. Allergic Anaphylaxis • The intestine and liver are engorged, holding up to 60% of the animal’s total blood volume • A combination of smooth muscle contraction and hepatic swelling lead to occlusion of the hepatic vein. • Mediators are histamine, prostaglandins, and leukotrienes

33. Food Allergy • 30% of skin diseases in dogs are due to allergic dermatitis responded to ingested allergens • Both digestive tract and skin • These responses originate from food idiosyncrasies, metabolic abnormality, pharmacological reaction, and food poison • An irregularity in the consistency of the feces, severe with vomiting, cramps, and violent and hemorrhagic diarrhea………..SOON pruritic dermatitis

34. Food Allergy • Papular and erythematous dermatitis involving the feet, eyes, ears, and axillae or perianal area • Chronic cases may be hyperpigmented, lichenified, and infected, leading to a pyoderma • Protein-rich such as dairy products, wheat meal, fish, chicken, beef, or eggs

35. Atopic Dermatitis • A chronic multifactorial syndrome characterized by chronically inflamed and itchy skin • An association with environmental allergens such as house dust mites, pollens, and molds • Affected dogs presented with pruritis and then diffuse erythema • Chronic licking and scratching leads to hair loss, papules, scaling, and crusting; hyperpigmentation and lichenification

36. Atopic Dermatitis • Skin lesions occur most commonly on the ventral abdomen and the inguinal and axillary regions • Focal hot spots in dogs: the cellular infiltrate with the lesions contains mast cells, Langerhans cells, and γ/δ T cells. Secondary bacterial or yeast infections complicate the disease • Oral, respiratory, or precutaneous routes….the latter route is reflected by lesions on face, feet, and ears-contact areas

37. Diagnosis of type I Hypersensitivity • A hypersensitive animal is given an intradermal injection of an allergen, this provokes local inflammation • This wheal and flare response reaches maximal intensity within 30 minutes and disappers within a few hours • A late-phase reaction occurs 6-12 hours after injection of an allergen

38. Diagnosis of type I Hypersensitivity • Vasoactive molecules are released within minutes to produce redness (erythema) as a result of capillary dilation, as well as circumscribed edema (a wheal) due to increased vascular permeability • An erythematous flare is due to arteriolar dilation caused by a local axon reflex

39. Diagnosis of type I Hypersensitivity • Passive cutaneous anaphylaxis test (PCA): dilutions of test serum are injected at different sites into the skin of a normal animal • After waiting for 24 to 48 hours, the antigen solution is administered intravenously • An immediate inflammatory response in each injection site-a positive reaction

40. Diagnosis of type I Hypersensitivity • The injected antibodies may remain fixed in the skin up to 8 weeks • Inject the test animal intravenously with Evans blue dye • The dye binds to serum albumin and does not normally leave the bloodstream • The dye-labeled albumin enters the tissue fluid and forms a striking blue patch in an inflammation site

41. Diagnosis of type I Hypersensitivity

42. Desensitization Therapy • Allergy shot-injections of the offending allergen • Promotion of IgG rather than IgE production and reduce the recruitment of inflammatory cells • This reduces mast cell and eosinophil numbers in the lung, as well as infiltration of CD4+ T cells and eosinophils in the skin • A shift from Th2 to Th1 cells • The desentization activate CD8 T cells that induce

43. Desensitization Therapy dendritic cells to produce IL-12 and IL-18, which synergize in promoting Th1 responses • Treg cells are stimulated to produce IL-10, thus inhibiting IgE production, mast cell activation, and leukotriene release • Small amounts of dilute aqueous solutions of antigen are administrated; over a few weeks, the dose is gradually increased

44. Desensitization Therapy