Type II HSR

Type II HSR

2014 Nov.
1. Complement dependent HSR (opsonization & phagocytosis)
2. Antibody dependent cellular cytotoxicity
3. Antibody mediated cellular dysfunction
The antigen is on the surface of cells + Ab →→ Ag-Ab reaction may be one of three effects:

Type II hypersensitivity 1. Complement dependent HS-reactions

2014 Nov.
Complement activation and lysis of the target cells after opsonization & phagocytosis. The complement here is C3b, the Ig is IgG, IgM

Clinical examples of HSR IIComplement dependent reactions

a- Autoimmune hemolytic anemia: There are auto-antibodies against the RBC-antigens. These auto-abs are of IgG or IgM type. Both can activate the complement and result in RBCs lysis or alternatively, IgG may opsonize the RBCs to be engulfed by the phagocytic cells in the spleen & liver.
2014 Nov.

2014 Nov.

Professor Intisar Salim Pity
b- Mismatched blood transfusion



Mismatched blood transfusion can result in a severe and life threatening hemolysis. For example, giving a blood of group A to a recipient of blood group B, then the anti A antibodies in the serum of the recipient will agglutinate and damage the transfused RBCs of the donor.
2014 Nov.


c- Erythroblastosis fetalis, only occurs in cases of Rh-ve mother & Rh+ve foetus). The maternal anti-D (anti-Rh) antibodies, which are of IgG type pass through the placenta and destroy the fetal RBCs. (Unusual in the first pregnancy & the antibodies developed after previous exposure to D-antigen, i.e. Rh+ve blood)
2014 Nov.


2. Antibody dependent cellular cytotoxicity in which the antibody molecule provides a link between the natural killer cell (or macrophage) and the Ag on the surface of the target cell without phagocytosis & without activation of complement →Drilling holes by perforin & granzyme. 2014 Nov.

3. Ab- mediated cellular dysfunction

b. Hashimoto thyroiditis: Ab formed are against TSH receptor of thyroid epithelial cells, locking the site of TSH action, resulting in hypothyroidism.
2014 Nov.
Professor Intisar Salim Pity
* c. Grave’s disease: Here the antibodies formed against TSH receptor of thyroid epithelial cells themselves act as TSH leading to continuous thyroid stimulation with a resultant thyrotoxicosis). Sometimes antibodies are formed against specific receptor & block its effect.

Type III HSR (Complex HSR)

Characterized by immune complex formation either locally in certain tissue or circulating in the blood & deposition in various tissues.
2014 Nov.
Professor Intisar Salim Pity



1. Binding of the antibodies (IgG, IgM) to the soluble antigen forming antigen-antibody complexes will activate the complement components (C3a, C4a, C5a, C5b).
2014 Nov.

2014 Nov.

2. Ag-ab complexes + activated complements in neutrophil emigration & cause vasodilatation and increased vascular permeability (i.e. acute inflammation). The end result will be tissue (endothelial) damage.

2014 Nov.

The process of inflammation of the wall of blood vessels is called vasculitis → Endothelial destruction → stimulates formation of thrombosis → may occlude the vessel lumen → tissue ischemia & necrosis of the organ or tissue supplied by that BV.

Acute post-streptococcal glomerulonephritis which develops 1-2 weeks following throat infection. The streptococcal antigens pass into the blood, then antibodies develop against them and react to form the ag-ab complexes which precipitate on the basement membrane of the glomerular capillaries. These complexes will activate complement components and cause the inflammation (vasculitis) & endothelial damage. The patient presents clinically with hematuria and oliguria.
2014 Nov.
Clinical examples of localized HSR III

Examples of systemic HSR III

A- Serum sickness B- SLE
2014 Nov.

Systemic lupus erythematosus

It results from auto-antibodies against nuclear components (DNA, histones, etc.). These are normally sequestered inside the nucleus where they are hidden from the antibodies, but they are released following tissue injury; e.g., a viral infection and are quickly bound by the patient own antibodies. The antigen-antibody complexes will deposit in the basement membranes of the glomeruli, lungs, joints, skin, lymph nodes…etc, where they induce complement fixation, inflammation & tissue damage 2014 Nov.

Clinical Features of Systemic Lupus Erythematosus

2014 Nov.

2014 Nov.

Type IV hypersensitivity
Type IV hypersensitivity is characterized by cell-mediated response rather than antibodies. Specifically T lymphocytes are involved in the development of the sensitivity, hence called cell-mediated hypersensitivity. T lymphocytes (CD4+) are activated by a variety of non-degradable agents like bacteria, fungi and protozoa…etc. 2014 Nov.
*

Delayed HSR

2014 Nov.
* Type IV hypersensitivity is of 2 types
Cellular cytotoxicity

Delayed HSR (Type IV HSR)

The antigen-specific CD4+ T cells will be activated → secretion of a variety of effector molecules (cytokines) → macrophage accumulation, activation & modification to epithelioid cells → granuloma.Many epithelioid cells may unite together to form giant cells. 2014 Nov.
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2014 Nov.

* Granuloma
Granuloma is a special type of Delayed HSR.TB, leprosy, syphilis … etc.

B- Cellular cytotoxicity: This reaction is mediated by the cytotoxic CD8 +ve T-lymphocytes which recognized antigen on target cells. E.g.: graft rejection virus infection tumor immunity
2014 Nov.
* The cytotoxic CD8 +ve T-lymphocytes kill the target cells by perforin & granzyme.

2014 Nov.

Professor Intisar Salim Pity
* Different Types of HSR
Character
HSR I Anaphylactic
HSR II(Cytotoxic)
HSR III(Immune complex)
HSR IV(delayed/cytotoxic)
Ab:
IgE
IgG, IgM
IgG, IgM
None
Antigen
exogenous
cell surface
soluble
Tissues, M.O.
Response time
minutes
minutes-hours
hours -months/ years
2-3 days
Main component
basophil & eosinophil
antibody & complement
Ag-ab complement &phagocytes
monocytes & lymphocytes
transferred with
antibody
antibody
antibody
T-cells
examples
asthma, hay fever
erythroblastosis fetalis, ABO incompatibility


TB & other causes of granuloma