Unit 1 - Immunology
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Lecture 1 - Introduction
Immunity: is resistance to disease
Immune system: collection of cells, tissues, molecules
that mediate response.
Immune response: Coordinated reaction of cells and
molecules to infectious disease.
Immunology: Is the science that study immune system
and its response to pathogens
Function of the immune system:
Prevent infection
Eradicate established infection
Types of immunity
1) Innate immunity:Exterior defense mechanism
Characteristics of innate immunity
1) Preexist 2) Not specific 3) No memory
Types of innate immunity:
1. Anatomic barrier( skin, mucous membrane)
2. Physiologic barriers( tempretire, PH, oxygen)
3. Chemical barriers( Lysozyme, Defensin, Interferon,
complement)
4. Cellular barrier: Neutrophils, Macrophage, Natural
killer cells and dendritic cells.
5. Toll-like receptors:It presents on phagocytic cells that
recognize broad molecules on pathogens enhancing
phagocytosis. It is called pattern recognition receptors
or pathogen associated molecular patterns.
2) Adaptive immunity
Characteristics of Adaptive immunity
1) Specificity 2) Diversity 3) Memory
4) Self non self-recognition 5) Clonal expansion
Central cell in the adaptive immune response
Lymphocytes
1- T lymphocytes-----cell mediated immunity
2- B lymphocytes-------humoral immunity
Antigens (Ag): any molecule that can be specifically
recognized by the adaptive immune system
Epitope: is a restricted part of Ag (short sequence of
sugars, a.a., that bind with antibodies (Abs).
Hapten: a small molecule had a low molecular weight
that cannot initiate an immune response unless its coupled
with a large carrier molecule
Super antigen: certain bacterial toxin (Staphylococcal
enterotoxins can bind to multiple T cells by binding to
T-cell receptor variable beta regions to alpha chain of
class II major histocompatibility complex on antigen
presenting cells.
Unit 1 - Immunology
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Factors determining antigenicity
1. Degree of foreignness
2. Molecular size:100000 dalton
3. Chemical compositions: proteins-polysaccharide-lipid-
nucleic acids
4. Susceptibility to antigen processing
5. Genotype
6. Dose of immunogens
7. Route of adminstration
8. Adjuvants:substanc mix with Ag to enhance
immunogenicity(Alum-Aluminum potassium sulfate)
Generation of mature lymph. first occurs in the embryo in
-yolk sac
-fetal liver
-fetal bone marrow and continues throughout life
in birds /lymphoid organs called Bursa of fibricius
(primary site of B-cell maturation)
In humans –BM and other lymphoid tissue serve as Bursa
equivalent
Lymphocytes:
B lymphocytes (B cells)
T lymphocytes (T cells)
Important for the adaptive immune response.
B cells:
Surface receptor = Immunoglobulin (Ig).
Humoral Immunity.
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Thymus
Its flat, bilobed organ situated above the heart. Each lobe
is surrounded by a capsule divide into lobule and
separated from each other by a trabeculae.Each lobule is
organized into cortex and medulla.
Hormones (thymosin, thymulin )and (enzymes like
adenosine deaminase)
Progenitor T cells in hematopoiesis in bone marrow then
ente thymus and acquire differentiation markers during
development calld CD markers (CD) markers.
Immature double negative (CD3+ CD4- CD8-) then
immature double positive thymocytes (CD3+ CD4+
CD8+) then mature single positive single negative
thymocytes (CD3+ CD4+ CD8-)(CD3+ CD4 –CD8+)
Thymic education and selection
The property of mature T cells is recognized only
foreign Ag (non self)+self MHC molecule. This can be
achived by selection process
Negative selection.
Positive selection.
The two processes called lymphocytes teachings.
Negative selection
Any lymph. Acquire receptors with high affinity for self
Ags will be die by a programmed cell death (apoptosis).
This occurs in the medulla by macrophages and dendretic
cells. (95-99%)
Positive selection
Any lymph. Acquire receptors recognize foreign Ags+
self MHC molecule will allow to mature and expand and
survive (1-5%). This occurs in the cortex of the thymus by
epithelial cells.
Lymphocytes homing
Lymphocytes leave thymus to sec. lymphoid organs (LN)
and to sites of inflammations through high endothelial
venules (HEV) by binding to specific receptors on lym.
and cell adhesion molecules on HEV after that lym.
homing to different tissues (GALT, MALT, skin dermal
endothelial venules ) by a cascade of interactions between
adhesions molecules on lym. And other cells.
Lymph nodes
Bean shaped, encapsulated ,containing a reticular network
packed with lymp., macrophages and dendretic cells .
Consist of 3 layers: Cortex, Paracortex & Medulla.