11 - Type IV hypersensitivity

Question 1

What is the definitely of IV Hypersensitivity

Answer 1

Cell mediated hypersensitivity involving Tcells and macrophages with no antibody involved
following lesion is called a granuloma
AKA delayed hypersensitivity bc its takes 12 hrs to develop and response lasts for days
major vet application is ID skin tests

Question 2

What is mycobacterial dz?

Answer 2

bovine tuberculosis (as seen in wood bison) and johne’s dz
Micros live in intracellularly in macrophages and are protected by a waxy coat. They are controlled by cell mediated immunity by cytotoxic T cells and more macrophages. They are only partially effective. They cause lg granulomas called tubercles and are used to diagnose tuberculosis

Question 3

What is skin testing?

Answer 3

A test for current or previous infection with intracellular bacteria
the principle is to inject purified, killed, cell extra intradermally (ex tuberculin for tuberculosis and johnin for bovine paratuberculosis)
memory T cells will then respond to mycobacterial proteins in infected individuals
we then observe swelling for 72-96 hrs

Question 4

In skin testing, what happens once the bacteria is injected?

Answer 4

antigen phagocytosed by langerhans cell (macrophage) and moved to lymph nodes
activation of memory T cells to divide and migrate back to site of antigen to then attract more myphocytes, macrophages and basophils

Question 5

During skin testing, how do false positives and negative reactions happen?

Answer 5

false pos arise from cross reaction w/ similar proteins from other mycobacteria
neg reactions bc no previous sor current infection, no memory t cells, purified extract doe snot elicit an immune response within 72 hrs

Question 6

What is allergic contact dermatitis?

Answer 6

When highly reactive chemicals bind to skin proteins, such as formaldehyde, poison icy and insecticides in flea collars
they can also provoke cell mediated immune response, delayed hypersensitivity
it causes inflammation, severe pruritus and possibly even skin vesicles

Question 7

Give a quick summary of type IV immunity, cell types involved, speed of onset, testing and its purpose

Answer 7

Lymphocytes and machrophages in lesions (called granulomas)
delayed onset of 12hs and response lasts for days
used in testing for cell mediated immune response as evidence for infection (especially for mycobacterial infections)
involved with allergic contact dermatitis