Allergy

Question 1

Describe the immunology of skin prick testing

Answer 1

Type 1 allergy
Allergen specific IgE antibodies bind to specific allergen
Triggers intracellular casade
Mast cell degranualation and release of histamines and other mediators

Allergen extract applied as drops

Top layers of epidermis punctured with lancet

A wheal with flare response after 15 minutes is positive

Result needs interpretation in clinical context

Question 2

Describe the immunology of ELISA

Answer 2

• plastic well coated with antibody
• patients serum is added
• if the antigen is present then it binds to the antibody
• add secondary detection antibody with enzyme
• add substrate
• look visible colour change

Question 3

Describe the immunology of patch testing

Answer 3

• antigen impregnated patch applied to the back
• antigen can penetrate the skin
• if contact dermatitits then mediated by effector T cells
• small molecule can usually penetrate the skin and forms protein-hapten complex, this is picked up Langerhan cells and migrate to lymph nodes
• antigen processed and presented in the context of MHC2 molecules
• activated t cells migrate to dermis
• TH1 release IFN-gamma and various other cytokines
• results read after 2 days

Question 4

Describe the immunology of IGRA

Answer 4

• takes blood from patient
• specific antigens to MTB added (ESAT-10, CFP-10)
• if previous Tb exposure then effector memory th1 recognises antigen
• release of IFN-g
• Detected using ELISA type method
• IFN-g antibodies on the well
• if t cells releases IFN-g then it binds
• add secondary antibody with detection enzyme
• add substrate
• dot indicates positive reaction