Hypersensitivity Hypersensitivity Reactions type Reactions type IVIV

PhD. student kefah F.Hasson2014

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 24-72 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

INTRACELLULAR PATHOGENS INTRACELLULAR PATHOGENS INDUCE DELAYED TYPE INDUCE DELAYED TYPE

BACTERIAM.tuberculosisBrucella abortusListeria monocytogen

VirusMeaslesHerpes simplex

FungusHistoplasmaCandidaprotozoaLeishmaniaOthersIvy poisonHairs dyeMetals poisonNickel salts

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 Allergic Contact Dermatitis Response to Poison IvyPoison Ivy

Granuloma Formation from DTHGranuloma Formation from DTH Mediated by Chronic Inflammation Mediated by Chronic Inflammation

Four types of Hypersensitivity ReactionsFour types of Hypersensitivity Reactions

YY IgE

Fc recep-tor

Histamine

Mast cells

Type I Type II

Type III Type IV

YY IgG

Killer cellFc receptor

Target cell

YAb

Complement

Target cell

Y

Y

Y

Y

ComplementAg

Ab

NeutrophilsCytokines

Th cell

Th

Macrophage

Activated MacrophageEnd

othe

lial

cel

lsAg

Ag

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.