Immunology, allergic cell-mediated response

The interaction of a chemical (hapten) with epidermal proteins (carrier) can result in a hapten-carrier complex capable of activating skin-associated lymphoid tissue (sensitisation) and dissemination of antigen-specific T l)unphocytes (induction). Subsequent encoimter with the same or cross-reactive chemicals can result in the elicitation of a characteristic inflammatory skin reaction. The clinical condition is referred to as allergic contact dermatitis and is characterised by erythema, oedema, vesiculation and pruritus. Allergic contact sensitisation is, therefore, classed as a cell-mediated immunological response to chemicals that contact and penetrate the skin. 

Coombs and Gell (1963) have classified all immunologic (allergic) reactions into four types (I to IV). The classification of Types I to III depends on whether antigen or antibody is cell-fixed or in solution. Type IV is cell-mediated and is typified in the skin by responses such as the tuberculin reaction which develops macroscopically over 36-48 hr and lasts for 72-96 hours. This is the classical delayed hypersensitivity reaction. 

A.4.1.2 For the purpose of this chapter, sensitization includes two phases the first phase is induction of specialized immunological memory in an individual by exposure to an allergen. The second phase is elicitation, i.e., production of a cell-mediated or antibody-mediated allergic response by exposure of a sensitized individual to an allergen. 

Anaphylactic shock, the most severe type of anaphylaxis, occurs when an allergic response triggers a quick release from mast cells of large quantities of immunological mediators (histamines, prostaglandins, leukotrienes), leading to systemic vasodilation (associated with a sudden drop in blood pressure) and bronchoconstriction (difficulty in breathing). Anaphylactic shock can lead to death in a matter of minutes if untreated. 

Introduction. The guinea-pig has long been known for its rather uniform anaphylactic response and its high sensitivity to the prominent allergic mediator, histamine. The origin of histamine, as well as of most other mediators of immediate hypersensitivity, has been traced to mast cells which in human lung are found at two distinct anatomical sites, the surface of the bronchial mucosa and around the venules in the deeper connective tissue. Mast cell activation by immunologic and other stimuli in this double location may be responsible for the distinct acute and subacute phases of respiratory distress (12). 

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