Immune Injury
• Hypersensitivities
• Autoimmune Disorders
Immune Injury
Autoimmunity
Immature or defective T-cells
Exposure to normally sequestered antigens
Cross reactions
Thyroiditis
SLE
Rheumatoid Disorders
Diabetes
Sometimes genetic predispositions to autoimmunity
“Hypersensitivities”
Why in quotes?
Some are truly “hyper” reactions, e.g. allergies.
Others are due to non-self although not by
their nature harmful agents, e.g. transfusion or
transplantation reactions
Some may be caused by normal immune
reactions to infectious agents
Four Types
I anaphylactic type
II cytotoxic type
III immune complex type
IV Delayed-type hypersensitivity
Three are humoral, immediate types
can be transferred with serum
“passive” hypersensitivities
Type IV is the only cell-mediated
type, would require transfer of
lymphocytes for “passive”
sensitization
They all require a sensitization stage
and time for immune response to
develop
Later exposure is called the
challenge stage
The term “immediate” refers only to the
challenge stage. In the first three types,
preformed antibodies cause immediate and
usually very obvious reactions
CMI, DTH: even though T-cells are already
activated, they do not travel to site as
quickly as humoral antibodies. May take a
few days before reaction is observable.
Anaphylactic Type
local or regional: hay fever,
animal dander, food allergies
Systemic: insect venoms,
injected drugs e.g. radio-opaque
dyes, foods
allergy shots
Sensitization
Stage
Effects of Systemic Anaphylaxis
• Vascular changes – dilation and increased
permeability lead to shock
• Effects on smooth muscle – constrict
bronchioles
• Affect heart action
Long-term
Treatments
• Allergy Shots – what’s the theory?
• Testing for and avoidance of allergens
Symptomatic:
• Antihistamines
• Anti-inflammatories
• For systemic anaphylaxis, epinephrine
Cytotoxic Type
HDN
Transfusion Reactions
Autoimmune Hemolytic Anemias
Idiopathic Thrombocytopenia Purpura
Which one does not require a
sensitization stage???
May also be due to a foreign
substance that attaches to a cell, e.g.
some drugs, some bacteria
Complex-Mediated Injury
• May occur after some infections
• Autoimmune disorders
• Serum Sickness
• Arthus Reaction, a local, deliberately caused
response
Effects
Inflammation especially in small
blood vessels, glomeruli, joints
Accumulation of neutrophils and
macrophages
Tissue damage
Role of Complement
• In which types of immune injury is C’
involved?
• Cytotoxic Type
• Complex-Mediated Type
Although some damage may be done by
antibody-antigen alone, even without
C’ activation
Delayed Type Injury
Contact Sensitivity
Tuberculin Reaction
Sensitization
Stage
Part of Sensitization Stage and also occurs at
beginning of Challenge Stage
Activation of Tc may follow
Cytotoxic T cell activity is one form of
Cell-Mediated Immunity
Tuberculin Response is another.
This is the one most often called DTH.
Contact Hypersensitivity is another
Contact Hypersensitivity
• Formaldehyde, latex gloves, poison ivy, poison
oak, material in flea collars
• Material attaches to skin cells. T-cells are
activated and attempt to destroy & remove the
altered skin cells
• Effects: mild erythema to severe inflammation,
blister formation. Because of itching, the host
causes additional damage
DTH or Tuberculin Rx’n
• Activated T cells
• Secrete lymphokines
• Recruit many other lymphocytes &
macrophages to the area
• So only a minority are antigen-specific cells
• Tissue Build-up
• Granuloma Formation
Conclusions
Immune injuries occur under a variety of
circumstances
The mechanisms must have derived from protective
measures. Else they would not have persisted
evolutionarily
Some agents may cause several of the types of
immune injury, e.g. penicillin
Autoimmune Disorders may exhibit a variety of
immune injuries
End of our coverage of Immune
Injury