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Biochemistry Hypersensitivity IV and V

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Biochemistry Hypersensitivity IV and V Description of Module Paper : 16 Immunology Module : 30 Hypersensitivity IV and V Principal Investigator Dr. Sunil Kumar Khare,Professor Dept. of Chemistry, I.I.T. Delhi Paper Coordinator Dr. M.N.Gupta, Emeritus Professor and Dept. of Biochemical Engg. and Content Writer Biotechnology, I.I.T. Delhi Content Reviewer: Dr. Prashant Mishra, Professor Dept. of Biochemical Engg. and Biotechnology, I.I.T. Delhi 1 Immunology Biochemistry Hypersensitivity IV and V Subject Name Biochemstry Paper Name 16 Immunology Module Name/Title 30 Hypersensitivity IV and V Dr. Vijaya Khader Dr. MC Varadaraj 2 Immunology Biochemistry Hypersensitivity IV and V 1. Objectives To understand the three types of class IV hypersensitivity reaction: contact dermatitis, tuberculin reaction and granulomatous hypersensitivity reaction. To explain how machanistically all the three types follow the same route. To learn how certain diseases caused by infectious agent have involvement of type IV hypersensitivity To understand type V hypersensitivity reactions which occur because of chronic stimulation 2. Concept map 3 Immunology Biochemistry Hypersensitivity IV and V Type IV hypersensitivity is also called delayed type as results are seen from 48 hrs-28 days ! In the three variants of type IV, the delay is of different time periods. We will also look at the type V hypersensitivity which was introduced as a separate class after Coombs and Geller classification. This hypersensitivity is involved in some autoimmune diseases. Contact with some substances can cause contact dermatitis. Injection of some antigens derived from infectious agents can be used as a test for hypersensitivity towards that microbe. When some microbes persist, it causes formation of granulomes. All are examples of delayed hypersensitivity. On the other hand, a variant of type II hypersensitivity when antigen is in fact an antibody against a host antigen causes chronic stimulation. This is classified as type V hypersensitivity by some workers. Type IV hypersensitivity In Coombs and Gell classification, all hypersensitivity reactions which take > 12 hrs to develop and are dependant upon cell mediated immunity are classified as Type IV or delayed type hypersensitivity. Much after this classification, late phase IgE mediated reactions were discovered. These are at their maximum in the time period of 12-24 hours after the exposure to allergen. As we have discussed, these also involve Th2 cells. So, that definition of type IV sensitivity is not adequate. Type IV sensitivity cannot be transferred by serum but by T-cells. T-cells involved are sensitized T-cells, that is, they had encountered the specific antigen (allergen) before and this time recruit other cells to the site of the reaction. 4 Immunology Biochemistry Hypersensitivity IV and V Contact dermatitis appears within 72 hrs of exposure to allergen Figure 1 Obviously, the exposure is through skin which comes into contact with allergen. In Europe, the most common allergens are: Nickel Chromate Chemicals in rubber 5 Immunology Biochemistry Hypersensitivity IV and V In USA, poison ivy and poison oak are reported to be responsible for maximum reported cases of contact dermatitis. In poison ivy, the responsible compound is urushiol, an oily mixture ofcatechol derivatives with long hydrocarbon side chains. Urushiol is secreted by leaves of the poison ivy vine and related plants. Catechol derivatives are easily oxidized to reactive o-quinones which can react with cell surface molecules to generate allergens. The skin pigment melanin and melanoprotein, in fact, arises from similar reaction. Various metals like Ni and Cr present in jewellery and hooks/zipper of garments chelate with skin proteins to form allergens. Allergic dermatitis sometimes is observed on pathologist fingers because of constant exposure to formaldehyde - another reactive molecule. Other common chemicals are picric acid, aniline dyes, organo phosphates, plant resins and oils. Unless the allergen is liquid, normally hairy parts of the skin are not affected. 2,4 Dichlronitobenzene (DNCB) and similar compounds have been used to induce contact dermatitis in experimental animals. Most of these compounds which cause contact hypersensitivity act as haptens, react with skin cell surface molecules to form hapten-carrier conjugate to become immunogenic. Contact hypersensitivity is distinguished from other type IV reactions in being a epidermal phenomena. The langerhans cells (antigen presenting cells in the skin) are the first step in the chain which is involved in the hypersensitivity. 6 Immunology Biochemistry Hypersensitivity IV and V Figure 2: Langerhan’s cells as they appear in a section of the normal skin Langerhans cells originate from the family of follicular dendritic cells and are derived from bone marrow. These are about 3% of epidermis cells. With few hours (~ 4hrs) of using DNCB in mice, langerhans cells appear in draining lymph nodes. It is in lymph nodes that these cells act as APC and present antigen to T- lymphocytes. Figure 3: 7 Immunology Biochemistry Hypersensitivity IV and V The first phase is sensitization phase. This consists of uptake, processing and presentation of the allergen by local APC. Sensitization takes place about 10-14 days in humans. Exposure leads to absorption. The haptens reacts with skin protein and epidermal langerhans cells internalize the antigen. Figure 4 The hapten containing peptides produced by APC are now ready to be presented. APC, the langerhans cells migrate to paracortical areas of regional lymph nodes and present the allergy to CD4+ lymphocyte. These produce a population of memory T-cells. In humans, both dose (amount) response as well as concentration (DNCB per unit area) response correlations have been observed. There is a plateau beyond a certain level. DNCB amount per unit area determines the response. During the second and subsequent exposures, primed (memory) Th1 cells in lymph nodes appear at the skin. Triggered T-cells secret cytokines such as IFN-γ which stimulate keratinocytes to secret further cytokines and chenokines. 8 Immunology Biochemistry Hypersensitivity IV and V Figure 5: The delayed-type (type IV) hypersensitivity response is directed by chemokines and cytokines released by Th1 cells stimulated by antigen 9 Immunology Biochemistry Hypersensitivity IV and V Figure 6 Langerhans cells present the processed antigen in the form of hapten-peptides to the memory CD4+ T-cells. CD3 receptor of the T-cells is involved and T-cells release cytokines which include IL-2, IL-3, IFN-γ and GM-CSF. The released IL-2 binds to the receptors on T-cells and induce their proliferation. IFN-γ and TNF induce epidermis keratinocytes to express intercellular adhesion molecule including ICAM-1 in about 24-48 hrs of the exposure to the allergen. At 48 hrs, kerationcytes express HLA-DR under the influence of IFN-γ. Lymphocytes and macrophages have integrin LFA-1 on their surface which recognise ICAM- 1. The result is that lymphocytes and macrophages come to the site in the skin. Activated keratinocytes also release IL-1, IL-6 and GM-CSF promoting activation and proliferation of T-cells. GM-CSF also activates langerhans cells similarly. 10 Immunology Biochemistry Hypersensitivity IV and V Endothelial cells in the dermis also express adhesion cells and can get involved in accumulation of lymphocytes to the site. Figure 7 The reaction begins to fade after 48-72 hours. At this point macrophages and keratinocytes produce prostaglandin E which inhibit IL-1 and IL-2 production. T-cells bind to keratinocytes. The hapten-peptide is degraded by cellular mechanism. So, essentially, the type IV hypersensitivity is mediated by chemokines and cytokines secreted by Th1 cells. The clear roles of these and there physiological consequences is shown in Figure 5. Chronic diseases in humans which involve type IV hypersensitivity Most are due to infections from mycobacteria, protozoa and fungi. Some have already been mentioned. An illustrative list is: Tuberculosis Leprosy 11 Immunology Biochemistry Hypersensitivity IV and V Leishmaniasis Listeriosis Blastomycosis (a deep fungal infection) Schitosomiasis (due to worm infection) Sarcoidosis (presumably an infection disease) These all are caused as a result of chronic antigenic stimulation. Leprosy is of three types: tuberculoid, borderline and lepromatous.Both tuberculoide and borderline types involve type IV hypersensitivity Both boderline leprosy and sarcoidosis show lesions typical of granulomatous hypersensitivity Tuberculin-Type hypersensitivity This was first observed by Koch. Koch found that subcutaneous administration of tuberculosis (a lipoprotein antigen from mycobacterium tuberculosis) to TB patients led to the tissue at the site of injection become hard and swelling was also observed. The “tuberculin reaction” is now the basis of Mantoux test. In this test, a purified antigen which is protein derivative of tuberculin is injected into skin and consequences developed are observed at the site of injection after 72 hours. A positive test consists of red swelling. Figure 8: Clinical and histological symptoms of tuberculin type sensitivity Histology reveals that these leukocytes and macrophages infiltrate locally in the skin at the sight of injection. 12 Immunology Biochemistry Hypersensitivity IV and V Soluble antigens from many other organism (which include M. lepare and Leishmania tropica) produce similar responses. This hypersensitivity is also observed with some non microbial antigens such as zirconium
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