Type 4 hypersensitivity

What type of hypersensitivity is involved in skin disease with granulomas?

Type IV Hypersensitivity (Cell Mediated Hypersensitivity)

Which cells are involved in Type IV hypersensitivity?

T cells and macrophages

Are antibodies involved in Type IV hypersensitivity?

No

What is the lesion called in Type IV hypersensitivity?

granuloma

What is another name for Type IV hypersensitivity?

Delayed hypersensitivity

How long does delayed hypersensitivity take to develop?

At least 12 hours

How long does the Type IV hypersensitivity response last?

Days

What is a major veterinary use of Type IV hypersensitivity?

Intradermal (ID) skin tests

Name two common mycobacterial diseases involving delayed hypersensitivity.

Bovine tuberculosis and Johne’s Disease

Where do mycobacteria live in the body?

Intracellularly in macrophages

How are mycobacteria protected inside macrophages?

By a waxy coat

What immune response controls mycobacterial infections?

Cell mediated immunity

What cells attack mycobacteria?

Cytotoxic T cells and macrophages

What lesion often develops in mycobacterial infections?

Large granulomas called tubercles

How do skin tests for mycobacterial infections work?

By intradermal injection of purified bacterial extracts

What is injected in the TB skin test?

Tuberculin

What is injected in Johne’s disease skin test?

Johnin

What cells respond to the antigen in the skin test?

Memory T cells

When is swelling checked after skin testing?

72- 96 hours later

What type of cells phagocytose the antigen at the skin test site

Langerhans cells (a type of macrophage)

What causes false positives in skin testing?
Cross

reactions with other mycobacteria

What does a negative skin test mean?

No infection or memory T cells

What chemicals cause allergic contact dermatitis?

Formaldehyde, poison ivy, insecticides in flea collars

What type of hypersensitivity causes allergic contact dermatitis?

Delayed hypersensitivity (Type IV)

Symptoms of allergic contact dermatitis?

Inflammation, severe itching, sometimes skin vesicles

Summary: Which cells dominate in delayed hypersensitivity lesions?

Lymphocytes and macrophages

Summary: What is the speed of onset of Type IV hypersensitivity?

Delayed (at least 12 hours)

Summary: What are the clinical uses of delayed hypersensitivity?

Testing for cell mediated immunity and diagnosing mycobacterial infections