PhD. student kefah F.Hasson
2014


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 CD
4
+Th
1
.
Immune injury mainly caused by infiltration of mononuclear cells and lymphocytes , release cytokines .
2) Cytotoxicity of CD
8
+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

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

Four types of Hypersensitivity Reactions
Type I
Type II
Ag
Mast cells
Y
IgE
Fc receptor
Histamine
Target cell
Y
IgG
Fc receptor
Killer cell
Ab
Complement
Target cell
Type III
Ag
Complement
Ag
Th
Type IV
Th cell
Ab Macrophage
Cytokines
Activated Macrophage Neutrophils

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.