Lecture 26

What is Type II Hypersensitivity also known as?

Cytotoxic hypersensitivity.

What type of antigens do immune responses act against in Type II Hypersensitivity?

Cell membrane-bound antigens.

What are the two mechanisms of cell destruction in Type II Hypersensitivity?

Antibody dependent cell-mediated cytotoxicity by natural killer cells and complement mediated reactions through the classical pathway.

What antigens can stimulate a Type II hypersensitivity reaction

Antigens that are normally part of the cell membrane or those that are covalently bound to the cell membrane

What causes blood transfusion reactions?

RBCs from the donor have antigens that the recipient can recognise as foreign, therefore leading to agglutination due to antibody complement bounding

What antibodies may form following a blood transfusion?

IgM and IgG antibodies.

Which of the following animals has naturally occurring antibodies: Cats, Dogs, Horses, Cattle

Cats and cattle

What is the clinically important blood type found in cats

Out of their type A, B and Ab blood groups, cats with type A blood have a weaker agglutination/immune response compared to cats with type B blood.

What is the clinically important blood type found in dogs

Out of their 7 RBC antigens, only DEA 1.1 (and 1.2) is sufficiently antigenic to cause transfusion reactions which means transfusion with the other blood types would be less reactive

What is the clinically important blood type found in horses

Because horses have over 400 000 blood types, they do not have a universal donor but out of all of these, Aa and Qa blood types are the most antigenic

What is Neonatal Isoerythrolysis?

A hemolytic disease of the newborn common in foals and kittens. It a result of maternal antibodies attacking the neonate's red blood cells

How does Neonatal Isoerythrolysis occur in horses?

The mare produces antibodies against foreign RBC antigens, and the foal ingests these antibodies through colostrum after birth.

What is the result of excess antigen or antibody in Type III Hypersensitivity?

Soluble antigen-antibody complexes form and deposit in tissues, activating classical complement when bound and causing cellular damage.

What are two conditions associated with Type III Hypersensitivity and what are they.

Rhodococcus equi infection in foals which is a result of complexes depositing in the glomerular basement membrane or joints. Purpura haemorrhagica which results in vasculitis following streptococcus equi infection.

What are typical sites of deposition for Ag-Ab complexes in Type III hypersensitivity

Tissues such as blood vessel walls and glomerular basement membranes

What is unique about Type IV Hypersensitivity?

No antibodies are involved; it is solely T-cell mediated either through CD4 or CD8 cells

What are the 3 subtypes of type IV hypersensitivty reactions

• Contact dermatitis

• Tuberculin-type hypersensitivity

• Granulomatous hypersensitivity

What is the time frame for clinical signs to develop in Type IV Hypersensitivity?

48-72 hours after exposure.

What is contact dermatitis in Type IV Hypersensitivity?

Haptens penetrate skin → langerhan cells present antigne to CD4/8 → CD8 is activated to secrete cytokines

What is a Tuberculin-type hypersensitivity

A type of reaction from animals exposed to M. tuberculosis. It is a diagnostic test where animals are exposed to tuberculin intradermally → leading to a localized inflammatory response, typically characterized by induration and erythema at the site of injection.

What is Granuloma Formation in type IV hypersensitivities ?

A result of persistent antigen stimulation leading to macrophage activation and recruitment → formation of giant cells → granuloma formation

How does Diabetes Mellitus relate to Type IV Hypersensitivity?

It is a CD8+ mediated process against pancreatic islet cells, leading to cytotoxic destruction of insulin-producing cells.