Identify the type of hypersensitivity reaction in each photo.
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Verified step by step guidance

1. Step 1: Understand the four types of hypersensitivity reactions, which are Type I (Immediate), Type II (Cytotoxic), Type III (Immune Complex-Mediated), and Type IV (Delayed-Type).
2. Step 2: Recall that Type I hypersensitivity involves IgE antibodies and is typically associated with allergic reactions such as hay fever or anaphylaxis.
3. Step 3: Remember that Type II hypersensitivity involves IgG or IgM antibodies directed against cell surface or matrix antigens, leading to cell destruction, as seen in conditions like hemolytic anemia.
4. Step 4: Note that Type III hypersensitivity involves immune complexes (antigen-antibody complexes) that deposit in tissues, causing inflammation, as seen in conditions like systemic lupus erythematosus.
5. Step 5: Recognize that Type IV hypersensitivity is mediated by T cells and does not involve antibodies, typically manifesting as contact dermatitis or tuberculin skin reactions.

Key Concepts

Hypersensitivity Reactions

Hypersensitivity reactions are exaggerated immune responses that can cause tissue damage and disease. They are classified into four types: Type I (immediate), Type II (cytotoxic), Type III (immune complex-mediated), and Type IV (delayed-type). Each type involves different immune mechanisms and can manifest in various clinical symptoms, making it essential to identify the type for appropriate diagnosis and treatment.

Type I Hypersensitivity

Type I hypersensitivity, also known as an allergic reaction, occurs when the immune system overreacts to an allergen, leading to the release of histamines and other mediators from mast cells. This can result in symptoms such as itching, swelling, and anaphylaxis. Common examples include allergic rhinitis, asthma, and food allergies, which are often triggered by substances like pollen, dust mites, or certain foods.

Type IV Hypersensitivity

Type IV hypersensitivity, or delayed-type hypersensitivity, is mediated by T cells rather than antibodies. This reaction typically occurs 24 to 48 hours after exposure to an antigen and is characterized by inflammation and tissue damage. Common examples include contact dermatitis from poison ivy and the tuberculin skin test for tuberculosis, where a localized reaction indicates prior exposure to the antigen.