Examples of Arthus reaction in the following topics:
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- In immunology, the Arthus reaction is a type of local type III hypersensitivity reaction.
- Type III hypersensitivity reactions are immune complex-mediated.
- The Arthus reaction involves the in situformation of antigen/antibody complexes after the intradermal injection of an antigen (as seen in passive immunity).
- If the animal/patient was previously sensitized (has circulating antibody), an Arthus reaction occurs.
- Arthus reactions have been infrequently reported after vaccination against diphtheria and tetanus.
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- A hypersensitivity reaction refers to an overreactive immune system triggered by allergies and autoimmunity.
- Hypersensitivity (also called hypersensitivity reaction) refers to undesirable reactions produced by the normal immune system, including allergies and autoimmunity, and are commonly mediated by antibodies.
- These reactions may be damaging, uncomfortable, or occasionally fatal.
- Hypersensitivity reactions require a pre-sensitized (immune) state of the host .
- Associated disorders: Serum sickness, Arthus reaction, Rheumatoid arthritis, Post streptococcal glomerulonephritis, lupus Nephritis, Systemic lupus erythematosus (SLE), Extrinsic allergic alveolitis (Hypersensitivity pneumonitis).
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- The reaction can take hours, days, or even weeks to develop, depending on whether or not there is immunlogic memory of the precipitating antigen.
- Skin response to a hypersensitivity of this type is referred to as an Arthus reaction, and is characterized by local erythema and some induration.
- After an antigen-antibody reaction, the immune complexes can be subject to any of a number of responses, including complement deposition, opsonization, phagocytosis, or processing by proteases.
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- The reaction quotient is a measure of the relative amounts of reactants and products during a chemical reaction at a given point in time.
- The reaction quotient, Q, is a measure of the relative amounts of reactants and products during a chemical reaction at a given point in time.
- By comparing the value of Q to the equilibrium constant, Keq, for the reaction, we can determine whether the forward reaction or reverse reaction will be favored.
- As the reaction proceeds, assuming that there is no energy barrier, the species' concentrations, and hence the reaction quotient, change.
- Calculate the reaction quotient, Q, and use it to predict whether a reaction will proceed in the forward or reverse direction
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- Changes in temperature can affect the equilibrium state of a reversible chemical reaction.
- Reactions can be classified by their enthalpies of reaction.
- A diagram of the reaction coordinate for an exothermic reaction is shown in .
- Exothermic reactions will be shifted toward the reactants.
- Endothermic reactions, on the other hand, will be shifted towards product formation as heat is removed from the reaction's surrounding environment.
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- The reverse process is called a retro ene reaction.
- This is the same bond bookkeeping change exhibited by electrocyclic reactions, but no rings are formed or broken in an ene reaction unless it is intramolecular.
- The following examples illustrate some typical ene reactions, with equation 3 being an intramolecular ene reaction.
- Reaction 4 is drawn as a retro ene reaction, although this has not been demonstrated to be general for all reactions of allylic alcohols with thionyl chloride.
- A similar acid-catalyzed reaction of simple aldehydes with alkenes to give allylic alcohols, 1,3-diols or 1,3-dioxanes is known as the Prins reaction.
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- For example, combustion reactions are usually exothermic.
- In exothermic reactions, the products have less enthalpy than the reactants, and as a result, an exothermic reaction is said to have a negative enthalpy of reaction.
- For example, decomposition reactions are usually endothermic.
- Thus, an endothermic reaction is said to have a positive enthalpy of reaction.
- Significant heat energy is needed for this reaction to proceed, so the reaction is endothermic.
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- With few exceptions, the multitude of reactions discussed in this and other introductory texts are classified as ionic reactions.
- Here we shall consider two other classes of organic reactions: Free-Radical Reactions & Pericyclic Reactions.
- One type of "free-radical reaction", alkane halogenation has already been described.
- In contrast to ionic reactions, both free radical and pericyclic reactions may occur in the gas phase, as well as in solution in various solvents.
- Also, these nonionic reactions are more tolerant of spectator functional groups than are many ionic reactions.
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- The chemical reactivity of benzene contrasts with that of the alkenes in that substitution reactions occur in preference to addition reactions, as illustrated in the following diagram (some comparable reactions of cyclohexene are shown in the green box).
- Many other substitution reactions of benzene have been observed, the five most useful are listed below (chlorination and bromination are the most common halogenation reactions).
- Since the reagents and conditions employed in these reactions are electrophilic, these reactions are commonly referred to as Electrophilic Aromatic Substitution.
- The specific electrophile believed to function in each type of reaction is listed in the right hand column.
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- Alternative methods of preparing a wide variety of organometallic compounds generally involve an exchange reaction in which a given metal is either moved to a new location or replaced by a new metal, which may include B, Al, Ti, V, Fe, Ni, Cu, Mo, Ru, Pd, Sn, Pt, Hg & Pb.