★The immune system is a two -edged sword.
★Immunodeficiency states render humans easy to catch infections and possibly tumors.
★Hyperactive immune system may cause fatal disease and tissue injury (hypersensitivity reaction).
★Immunodeficiency disease:-
It means defects result in impaired resistance to microbial infections.
★Classifications:divided into:
1-primary type .
2-secondary type.
(a) Primary immunodeficiency disease:-
manifest in early childhood.
Genetically determined.
Further divided into:-
1-Deficiencies of antibody (B-cells).
2-Deficiency of cell mediated (T-cells)immunity.
3-Combined T-cells and B-cells Deficiency.
4-complement factor deficiency.
(b)Secondary immunodeficiency disease:-
deterioration in previously strong immune status.
Usually secondary to systemic conditions like:-
1-Diabetic mellitus.
2-Renal failure.
3-Liver failure.
4-Poor nutrition.
5-Cancers.
6-Broad spectrum antibiotics.
7-Prolonged steroid therapy.
8-Human immunodeficiency virus (HIV/AIDS).
★Hypersensitivity reactions:-
refer to exaggerated response of immune system to an antigen (foreign body).
The antigen that elicits the response is called an Allergen.
★cells and combs classification :-
Hypersensitivity reaction can be divided into 4 types:-
Types I,II and III are achieved by antibody.
Type IV reactions is achieved by T-lymphocytes.
★Type-I (Immediate hypersensitivity reactions).
occur when antigen binds to IgE antibodies attached to the surface of mast cells.
Leading to the release of intracellular granules which contain histamine.
Histamine causes peripheral vasodilation and an increased vascular permeability,resulting in local congestion and edema.
Histamine also cause bronchospasm.
Example : Bronchial asthma.
★Type-II(cytotoxic hypersensitivity).
Mediated by a circularing antibody.
Antigen on the surface of a cell (could be a normal component of the membrane or a foreign antigen ,such as apharmacological agent ,that adheres to the surface of the cells).
Example :Autoimmune hemolytic anemia.
★Type-III(immune complex disease).
Mediated by antigen - antibody complexes that activate complement.
The antigen - antibody complexes accumulate in the circulation and if not cleared , the complex lodge in the tissue , Where they initiate inflammatory reaction.... tissue destruction.
Example : collagen disease (Rheumatic fever and Rheumatoid arthritis).
★Type -IV(cell -mediated hypersensitivity).
Mediated by T-lymphocytes(delayed type hypersensitivity).
When T-cells reacts with the antigen , it releases lymphokines that draws macrophages in to the area and elicit inflammatory reaction.
Example: Contact Dermatitis.
