Kuby Immunology 6/e

Hypersensitivity Reactions type IV PhD. student kefah F.Hasson 2014

Characteristics  Interaction of primed T cells and associated antigen 

Involve reactions by T memory cells.



Reactions are delayed by one or more days (delayed

type hypersensitivity -DTH) . Infiltration of Mononuclear Cells ( Inflammatory response).



Delayed is relative because DTH response arise 2472 hours after exposure rather than within minutes.  Delay is due to migration of macrophages and T cells to

site of foreign antigens.



Reactions are frequently displayed on the skin:

itching, reddness, swelling, pain

Mechanism of type IV hypersensitivity 1) Inflammation and tissue injury mediated by CD4+Th1. Immune injury mainly caused by infiltration of mononuclear cells and lymphocytes , release cytokines .

2) Cytotoxicity of CD8+CTL

BACTERIA M.tuberculosis Brucella abortus Listeria monocytogen 

Virus Measles Herpes simplex 

Fungus Histoplasma Candida  protozoa Leishmania  Others 

Ivy poison Hairs dye Metals poison Nickel salts

INTRACELLULAR PATHOGENS INDUCE DELAYED TYPE

Effector phase

Diseases of Type IV (Cell-Mediated) : 1) Infectious delayed type hypersensitivity like : OT( Old Tuberculin ) test. 2) Contact dermatitis :like water blister . 3) Acute rejection of allogenic transplantation .

Allergic Contact Dermatitis Response to Poison Ivy

Granuloma Formation from DTH Mediated by Chronic Inflammation

Four types of Hypersensitivity Reactions Type II Type I Ag

Y

IgE

Y

Target cell IgG

Target Fc receptor cell

Complement Ab Neutrophils

Endothelial cells

Fc recepKiller cell Mast cells tor Ab Histamine Complement Type III Type IV Ag Ag Th

Macrophage

Th cell

Cytokines Activated Macrophage

Topic for exam The Gall & Coombs classification of hypersensivity reactions .  Type I ,II ,III ,IV hypersensivity reactions mechanism & example .  Immunological basis of the HDN caused by Rh incompatibility .  Mention the common diseases of each types of hypersensivity reactions. 