deck_21085681 Flashcards by Jorge Torres

Hypersensitivity reactions are classified based on the type of antibody produced as a result of the reaction. True or false?

False. They are classified based on the principal immunologic mechanism that is responsible for tissue injury and disease

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Classify the types of hypersensitivity reaction

Type 1: Immediate-type allergic reactions mediated by IgE, such as to food.

Type 2: IgG and IgM bind to antigens on cell surfaces, which induces a cascade of reactions that damages cell by activating the compliment system or by phagocytosis

Type 3: Circulating antigen-antibody immune complexes that depois in postcapillary venules, with subsequent complement fixation

Type 4: Delayed hypersensitivity reactions that are mediated by T cells.

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Type 3 hypersensitivity reactions require antibodies and cytotoxic T cells to occur. True or false?

False. That is Type 2

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Type 4 hypersensitivity reactions do not require antibodies, and are instead triggered by interactions between T cells. True or false?

True

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Type 1 Hypersensitivity reactions are mediated by IgE and Macrophages. True or false?

False. Its IgE and Mast cells

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What are the “fancy” terms for the consequences of a type 1 reaction

Rapid vascular leakage, mucosal secretions and inflammation

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What is the sensitization phase?

It’s the first exposure to an allergen.

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What happens when a non-atopic person is exposed to an allergen?

Nothing

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Explain the steps in the sensitization phase

A DC picks up the allergen, mounts it on MHC II, and presents it to a CD4 T cell.

The CD4 T cell differentiates into a Th2 cell, which, with the help of a T cell, gets a B cell to produce IgE specific for the antigen.

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Whats the effector phase?

Its when there’s a subsequent exposure a previously exposed allergen

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Explain the steps in the effector phase

Antibodies bound to the surface of mast cells detect the previously exposed antigen.

They degranulate, releasing histamine and lipid mediators, which cause vascular and smooth muscle response.

Inflammation comes as a late phase reaction due to cytokines and chemokines recruiting eosinophils and neutrophils

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Why is there swelling on a type 1 hypersensitivity reaction?

Because the mast cells release molecules that lead to an increased vascular permeability, which causes fluid, cells and proteins to be able to more easily exit the blood ducts and into tissue, leading to localized swelling.

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Most allergens are highly-soluble proteins. True or false?

True

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IgE has the shortest half life of all the Ig’s, but it becomes extremely stable once bound to a granulocyte’s receptor. True or false?

True

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Atopic people produce much higher amounts of IgM in response to allergens. True or false?

False. They produce IgE

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What type of cells can we expect to find in type I hypersensitivity reactions?

Th2, ILC2, mast cells, basophils and eosinophils.

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What does Th2 do in allergic reactions?

It secretes cytokines such as IL-4, IL-5 and IL-13 that, in combination with mast cells, eosinophils and ILCs, generates an inflammatory response to allergens.

IL-4 recruits eosinophils and more Th2 into tissues
IL-5 activates eosinophils
IL-13 stimulates epithelial cells to secrete more mucus.

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In an allergic reaction, what does Th2 produce and what does ILC2 produce?

Th2 produces IL-4, IL-5 and IL-13

ILC2 only produces IL-5 and IL-13

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Th2 are the first “responders” to an allergic reaction. True or false?

False. ILC2 reside in the tissues, and, as such, they can contribute to an early allergic inflammation before Th2 is generated and migrated to tissues.

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What happens when mast cells are activated?

They secrete granule contents
They secrete lipid mediators
They secrete cytokines

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No matter how the allergic person is exposed to an allergen, the reaction is always the same, as all IgE-mediated responses involve mast-cell degranulation. True or false?

False. How/where the person was exposed to also matters.

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How do antihistamines work?

They inhibit the effects of mediators on specific receptors and they can inhibit the synthesis of mediators

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How do corticosteroids work?

Study These Flashcards

General anti-inflammatory effects

If we can prevent an IgE from binding to a mast cell, we could prevent an allergic reaction. True or false?

Study These Flashcards

True

Reducing the amount of Th2 cells in the immune system is a way of dampening allergic reactions. True or false?

True

What is the advantage of IgG4 antibodies?

They act as an anti-antibody, as they bind to the allergen before IgE has a chance to do it. Another way to do it is by binding to the allergen alongside an IgE receptor on a mast cell. However, since IgG4 is bound to the mast cell as well, it has a suppressing effect, preventing the degranulation of the mast cell and stopping the allergic reaction.

Kids who eat dirt are less likely to develop allergies. True or false?

True

How can genetics influence allergic reactions?

Genes that regulate CD4 T cells and ILC2 differentiation and function

What the fuck is the point of allergies?

They are an evolutionary result of protection against parasites, noxious xenobiotics, environmental irritations and poisons.

A mismatched blood transfusion can be considered a type 3 hypersensitivity reaction. True or false?

False, it's type 2

Every autoimmune disease is a type 2 autoimmune reaction. True or false?

False. Most are, but some are type 3

In a type 2 hypersensitivity reaction, what antibodies can play a role in it?

IgG and IgM

In a type 2 HSN reaction, what happens when IgM stimulates the receptors at a cell surface, what happens?

It activates the classical compliment pathway, which gets the MAC to attack, leading to cell lysis.

In a type 2 HSN reaction, what happens if an IgG stimulates the cell surface receptors?

It stimulates the macrophages to phagocytose.

For a type 2 hypersensitivity reaction to begin, you need to have complement formation. True or false?

False. There is Type 2 with and without compliment formation

In a type 2 HSN reaction without complement formation, an antigen that binds to IgE will result in recruitment of eosinophils. True or false?

True

The problem with complement-free type 2 hypersensitivity reactions comes from the fact that the cells recruited by the interaction between antibody-antigen release inflammatory mediators which leads to cell lysis. True or false?

True

In a type 2 HSN reaction without complement formation, an antigen that binds to IgG will result in recruitment of eosinophils. True or false?

False. It will result in the recruitment of neutrophils and monocytes

All type 2 HSN reactions stem from an antigen (allergen) binding to a cell-surface antibody. True or false?

False. There is a complement-free type 2 reaction that is the result of an antibody (IgG) binding against a cell receptor.

When an antibody (IgG) binds to a cell receptor (and is not supposed to), we have a type 2 HSN reaction. True or false?

True.

In Type 3 HSN, we have an antibody binding to another antibody while both being soluble. True or false?

True.

Where do type 3 HSN start?

In the blood.

In HSN type 2 and type 3 reactions, where does the antibody bind?

To the Fc portion of the other antibody.

Type 3 HSN reactions only begin causing problems where the Ab-ab complex deposits somewhere. True or false?

False. While floating, they can activate the classical complement pathway, which leads to inflammation.

In theory, how many HSN reactions can a bad doctor give you?

Three. Type I (if you're alergic to something in the office) Type II (by fucking up a blood transfusion) Type III (serum sickness)

What is serum sickness?

You were sick, you were injected antibodies to fight said disease, but your body developed antibodies FOR the antibodies in the serum. This leads to the expected type 3 HSN reactions: complement pathway activation and deposition of the antibody-antibody complexes in tissues.

You can develop serum sickness to human antibodies. True or false?

False

What is the Arthus reaction?

An acute, localized inflammatory reaction that can happen when a foreign Ag is injected subcutaneously.

If macrophages clear immune complexes in the blood, how can type 3 reactions occur?

Too many immune complexes, not enough macrophages.

Which of the type 3 HSN reactions are localized and which are generalized?

Only the Arthus reaction is localized.

Th1 cells (which are the CD4+) secrete IFN-gamma, which activates the macrophages. True or false?

TRUTH NUKE

T cell-mediated tissue injury is a good description for type _ HSN reactions

Type 4

How can a type 4 HSN reaction occur?

In two ways: 1. Inflammation can be triggered by cytokines produced by CD4 T cells, in which tissue injury is caused by activated macrophages and inflammatory cells. 2. Direct killing of target cells mediated by CD8 cytotoxic T lymphocytes.

What is the consequence of a prolonged DTH response

Granuloma formation

In a type 4 HSN reaction, when does a granuloma form?

When it is very prolonged or when the pathogen cannot be phagocytosed.

What does each type of HSN reaction show?

Type 1: Failure in tolerance to innocuous antigens, driven by Th2 skewing and IgE amplification Type 2: How antibodies can target host cells (it really be your own fellas) Type 3: The importance of immune complex clearance and complement balance Type 4: Cell mediated immunity, vital for infection control, can drive chronic damage.

deck_21085681 Flashcards

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