Hypersensitivity reactions and types.pptx

A hypersensitivity reaction happens when the immune system mistakenly identifies harmless substances as harmful. There are several types of hypersensitivity reactions, depending on the class of substance that triggers it.

An antigen or allergen can refer to a toxic or foreign substance that causes an immune reaction. After detecting an antigen and perceiving it as a potential threat, the immune system mounts an immune response to dispose of it.

The body can produce different types of hypersensitivity reactions, depending on the antigen a person has exposure to and how the body responds to it.

This presentation discusses the different types of hypersensitivity reactions.
hypersensitivity reaction is an extreme or unnecessary immune response that the body has to an antigen.

There are four different types of hypersensitivity reactions. Some evidence suggests a potential fifth type, but this may actually be a subset of type 2 hypersensitivity reactions.

Each type of hypersensitivity reaction is an extreme immune response to an antigen. Each type of reaction differs based on the type of antigen the body identifies, what type of immune response the body generates, and how quickly the body produces the response.

Some people may refer to hypersensitivity reactions as allergies, as these are a form of hypersensitivity. Although people use these terms interchangeably, an allergic reaction typically refers to the signs and symptoms a person may experience, while a hypersensitivity reaction describes the immunological process that occurs in the body.

Type 1 hypersensitivity reaction
Type 1 hypersensitivityTrusted Source causes an immediate responseTrusted Source and occurs after a person has exposure to an antigen. With this type of reaction, the body responds to an antigen by producing a specific type of antibody called IgE.

There are different components that can trigger type 1 hypersensitivity responses, including antigens that come from:

food products, such as nuts, shellfish, and soy
animal sources, such as cats, rats, or bee stings
environmental sources, such as mold, latex, and dust
allergic conditions, such as allergic rhinitis, allergic asthma, and conjunctivitis
There are two stages to type 1 hypersensitivity: the sensitization stage and the effect stage.

During the sensitization stage, the person encounters the antigen but does not experience any symptoms. During the effect stage, the person has exposure to the antigen again. As the body now recognizes the antigen, it is able to produce a response that results in the symptoms that people typically experience with an allergic reaction.

Some physical symptoms of type 1 hypersensitivity can include:

rash
flushing
hives
itching
edema
wheezing
rhinitis
stomach cramps
Responses can also cause:

nausea and vomiting
shortness of breath
cardiac symptoms
loss of consciousness

1. Hypersensitivity reactions

2. introduction Hypersensitivity is defined as an exaggerated or inappropriate state of the normal immune response with onset of adverse effects on the body The lesions are antigen- antibody reaction form 4 types of immunologic tissue injury: type I, II, III, IV Based on the rapidity, duration & type of the immune response they are grouped into – immediate and delayed reactions

3. types Immediate – on administration of antigen the reaction occurs immediately(within seconds to minutes) & is mediated by humoral antibodies mostly. It includes Type I,II,III reactions Delayed – slower reaction takes 24-48 hours with prolonged effect & is mediated by cellular response. It includes Type IV reaction

4. Type I hypersensitivity State of rapidly developing or anaphylactic type of immune response to an antigen to which the individual is previously sensitised Occurs within 15-30 mins of antigen exposure Known as allergic or atopic disorders Mediated by humoral IgE antibodies Etiology : 1. Genetics(high IgE & low suppressor T cells in HLA-B8 type) 2. environmental pollutants increase mucosal permeability 3. Concomitant factors – viral URTI occurrence in susceptible individual Examples: ATS antisera, penicillin, wasp or bee sting

5. Pathogenesis Type I B lymphocytes, plasma cells, mast cells, basophils, eosinophils, neutrophils Sensitisation after host antigen contact – activation of B lymphocytes – differentiate to form IgE secreting plasma cells – IgE antibodies bind to the Fc receptor of mast cells, basophils surface – cell damage after firm contact – membrane lysis, influx of Na, water with degranulation of mast cells- basophils The granules contain chemicals & enzymes – histamine, serotonin, vasoactive intestinal peptide, chemotactic factors of anaphylaxis for neutrophils, eosinophils, leukotrienes B4 & D4. PGNs, PAF – this cause increased vascular permeability, smooth muscle contraction, early vasoconstriction and vasodilation, shock, increased gastric secretion, nasolacrimal secretion, migration of eosinophils, neutrophils at the injury site and in blood