6. Allergy & Hypersensitivity Flashcards
An allergy is generally defined as an ... hypersensitivity response. It requires ... to the antigen and generally occurs ... on second exposure.
Hypersensitivity involves recruitment of ... and sometimes .... ... cells are critical as they drive ... production. Mast cells are activated via ..., which trigger .... This includes the release of ..., ..., and .... Mast cells also release ... and ....
An allergy is generally defined as an IgE-mediated hypersensitivity response. It requires prior exposure to the antigen and generally occurs immediately on second exposure. Hypersensitivity involves recruitment of eosinophils and sometimes neutrophils. TH2 cells are critical as they drive IgE production. Mast cells are activated via IgE, which trigger degranulation. This includes the release of histamines, proteases, and chemotactic factors. Mast cells also release cytokines and secondary mediators e.g. membrane phospholipids.
Histamine can directly stimulate two different receptors, ...and .... ... are found in nerve terminals, such as .... Binding of histamine to H1 triggers an .... ... can be found on smooth muscles of .... Binding of histamine causes ... therefore contribute to ....
Histamine can directly stimulate two different receptors, H1 receptor and H2 receptor. H1 receptors are found in nerve terminals, such as sensory nerves of the conjunctiva. Binding of histamine to H1 triggers an itch response via the conjunctiva. H2 receptors can be found on smooth muscles of blood vessels, such as walls of conjunctival vessels. Binding of histamine causes vasodilation therefore contribute to conjunctival redness.
... ingest cellular debris and bacteria;... ingest antigen/antibody complexes. They attack ... that are coated with .... This process is driven by .... In allergic responses, ... still get recruited, however since there is no ... to ingest, they seem to be redundant in allergic reactions. However, it is a vital ....
Neutrphils ingest cellular debris and bacteria; Eosinophils ingest antigen/antibody complexes. Theyy attack parasites that are coated with antibodies. This process is driven by IgE. In allergic responses, eosinophils still get recruited, however since there is no antigen/antibody complexes to ingest, they seem to be redundant in allergic reactions. However, it is a vital diagnostic tool.
Is delayed hypersensitivity (type IV) an allergic response?
If the response is not immediate and IgE-mediated, it cannot be treated in the same way as a true allergic response. This includes drug toxicity and contact dermatitis.
Outline the clinical signs (~10) of an IgE-mediated allergic response.
• Intense itchiness
• Red eye
• Conjunctival cheomsis
• Blurred vision (due to swelling of cornea)
• Mucus discharge
• Lid thickening
• Giant/ Cobblestone papillae
• Limbal infiltrates
• SPK
• Corneal ulcer
What are the 4 main ocular allergy presentations?
• Acute rhinoconjunctivitis or Allergic perennial/ seasonal conjunctivitis (ARC) → pollen/mite
• Vernal keratoconjunctivtis (VKC) → allergen
• Atopic keratoconjunctivtis (AKC)
• Giant papillary conjunctivitis (GPC) → CL related
Vernal keratoconjunctivitis is a ... condition. It is mostly ..., but can also be .... This affects mostly .... This is not well managed with .... Clincal signs includes ..., ... and .... It is theorised that the initiating factors of VKC is ..... This is evident through finding large numbers of ... in tears, as well as high levels of ... found in .... Conjunctival tissue is full of many types of ..., particularly ..., indicative of .... However, the presence of ... and ... also suggest that VKC is part of ... as a late phase response.
Vernal keratoconjunctivitis is a recurrent/ chronic condition. It is mostly seasonal, but can also be perennial, especially in warmer climates. This affects mostly children and young male adults. This is not well managed with anti-allergy medications. Clincal signs includes giant papillae on upper tarsal conjunctiva, gelatinous limbal lesions and mucous discharge. It is theorised that the initiating factos of VKC is abnormal Th2 cells making the body hypersensitive to antigens. This is evident through finding large numbers of eosinophils/ neutrophils with TH2 lymphocytes in tears, as well as high levels of IgE found in tears and plasma. Conjunctival tissue is full of many types of inflammatory cells, particularly eosinphils, indicative of type I allergy. However, the presence of mast cells and TH2 CD4+ T cells also suggest that VKC is part of type IV hypersensitivity as a late phase response.
Vernal keratoconjunctivitis changes the structure of the ... conjunctiva. VKC causes infolding of the papillary epithelium, therefore forming a ... arrangement of .... Mast cells stimulates the secretion of ..., which forms ... which causes the papillae to ....
Vernal keratoconjunctivitis changes the structure of the tarsal conjunctiva. VKC causes infolding of the papillary epithelium, therefore forming a psuedo-glandular arrangement of goblet cells. Mast cells stimulates the secretion of mucin/ mucous, which forms mucin plug which causes the papillae to distend.
VKC causes structural abnormalities to the corneal ... and .... There are ... dots, which indicates .... These are mainly caused by .... Many corneal complications can result from VKC, such as ..., ..., ..., ..., ..., ..., ... etc.
VKC causes structural abnormalities to the corneal stroma and limbus. There are Horner-Trantas dots, which indicates lymphocyte and eosinophil infiltrates. These are mainly caused by eosinophillic protein deposition and calcification. Many corneal complications can result from VKC, such as SPK, shield ulcers, corneal scarring, keratoconus, dry eyes, limbal stem-cell deficiency, secondary infections etc.
Giant Papillary Conjunctivitis (GPC) is almost exclusively a result of ... and can occur with .... GPC has both ... (due to lens damage to ...) and also .... Similar to VKC and AKC, GPC involves lots of ... and high ... in tarsal conjunctiva. Some experiments found that ... on contact lenses may serve as an allergen. GPC causes similar ... abnormalities compared to VKC.
Giant Papillary Conjunctivitis (GPC) is almost exclusively a result of contact lens wear and can occur with any type of contact lenses. GPC has both mechanical (due to lens damage to tarsal conjunctiva) and also IgE-mediated. Similar to VKC and AKC, GPC involves lots of inflammatory cells and high IgE in tears in tarsal conjunctiva. Some experiments found that mucin coatings on contact lenses may serve as an allergen. GPC causes similar structural abnormalities compared to VKC.
Name an uncomplicated allergic conjunctivis. How is it diagnosed?
Seasonal rhinoconjunctivitis.
Measure tear IgE and conjucntival swabs for eosinophils.
Why is it important to distinguish the different mechanisms of allergic/ hypersensitivity responses?
Mast cell stabilisers/ Anti-histamines are only useful for IgE-mediated respnoses; Steroids/ NSAIDS are needed to control cellular responses.
