What are arthus reactions?

➢ The Arthus reaction(a local forms of IC diseases) involves the in situ formation of antigen/antibody complexes after the intradermal injection (or S/C) of an antigen. ➢ If the animal/patient was previously sensitized (has circulating antibody), an Arthus reaction occurs within 4h to 8h ➢ When antigen is injected into the skin, circulating IgG antibody that has diffused into the tissues forms ICs locally. ➢ Typical of most mechanisms of the type III HS, Arthus manifests as local vasculitis due to deposition of IgGbased ICs in dermal blood vessels ➢ The ICs bind Fc receptors on mast cells and other leukocytes, which creates a local inflammatory response with increased vascular permeability