Immunology-introduction
Immune system
• One of basic homeostatic mechanisms of
the body.
• Its function is the recognition of
foreign/dangerous substances.
• The dangerous substances trigger
complex reactions which result in
elimination of those substances.
Immune system
• Recognizes foreign/dangerous substances
from the environment (mainly microbes)
• Is involved in elimination of old and
damaged cells of the body.
• Attacks tumor and virus-infected cells.
Functions of the immune system
• Deffence
• Autotolerance
• Immune surveillance
Antigen
• Substance, that is recognised by the
immune system as a foreign and triggers
immune reaction (immunogenicity).
• Products of the immune reaction
(antibodies, T-lymphocytes) react with the
antigen.
Requirements of immunogenicity
• Foreign (unknown) for the immune system
• High molecular weight (> 6 kDa)
• Chemical complexity
Antigen – functional components
• Carrier part of the molecule
• Antigenic determinant- epitope (cca 5-7
aminoacids)
Antigen - epitopes, carrier part
Antigen - epitopes, carrier part
Antigen and epitope
Chemical composition of antigents
• Proteins – usually very good antigens.
• Polysacharides- usually only as a part of
glycoproteins.
• Nucleic acids- poor antigenicity, limited to
complexes with proteins
• Lipids – only exceptionally, best known are
sfingolipids.
Protective and nonprotective
antigens
• Protective antigens – elicit protective
immune response that leads to elimination
of the microbe.
• Non-protective antigens – elicit nonprotective
immune response, but it does
not lead to elimination of the microbe (e.g.
antibodies against HIV).
Hapten
• Low-molecular weight substances that trigger
immune reaction after binding to various
proteins of the body.
• They react with products of the immune reaction.
• Typical examples are metals (Cr, Ni) that trigger
type IV immunopathological reactions. Drugs
(antibiotics, local anestetics) cause type I
immunopathological reaction.
Immunogenicity of hapten
Cross reactivity of antigens
• Products of the immune reaction may, in some
conditions, react with substances that are very
different from the initial immunogen.
• Immunological cross-reactivity not necessary
mean similar chemical composition.
• The degree of cross reactivity may be different.
• Cross reactivity is important in pathogenesis of
several autoimmune diseases.
Cross reactivity of anntigens
High affinity Low affinity
Ab1
Ag2
Ab1
Ag1
Adjuvants
• Substances, that when mixed with antigen, nonspecifically
enhance immune reaction against
the antigen.
• Freud´s adjuvant: killed Mycobacterium
tuberculosis + water-in-oil emulsion. Used in
veterinary medicine.
• Alum precipitate - AL(OH)3 - used in human
medicine.
• Mechanisms: improved presentaion of the
antigen, fixation of the antigen in the place of
application..
Two branches of the immune
response
• Innate, nonspecific – very quickly
recognizes most foreign substances and
eliminates them. There is no memory.
• Adaptive, specific – high degree of
specificity in distinction between self and
non-self. The reaction requires several
days to be effectively triggered. There is
immune memory.
Cells of the immune system
• Main cells of the immune system
– Lymfocytes (T a B)
• Accessory cells of the immune system
– Granulocytes
– Monocytes
– Tissue macrophages
– Mast cells
– Dendritic cells
– NK cells
– Endotelial cells
– Thrombocytes, erythrocytes, fibroblasts, epitelial cells
Majority of immune system cell originate in bone marrow
Roitt/Broskoff/Male: IMMUNOLOGy, 4th ed
Differentiation of cells during
hematopoiesis
Differentiation of haematopoetic stem cell is
influenced by the local environment
Lymphocyte – central cell of the immune system
Auxiliary cells of the immune system
Antigen- presenting cells
Organs of the immune system
Thymus
Primary lymphloid organs Secondary lymphloid organs
Bone
marrow
Waldeyer´s ring (lymphs nodes,
tonsilis adenoids
Bronchus-associated lymphoid
tissue
Lymph nodes
Bone marrow
Spleen
Payer´s patch
Mesenteric lymph
nodes
Lamina propria
Urogenital lymphoid tissue
Lymph nodes
Lymph node
Roitt/Broskoff/Male: IMMUNOLOGy, 4th ed
The Spleen
Payer ´s Patches
High endotelial venules
• Specialized venules. The site where
lymphpocytes leave the blood stream and
migrate into lymph nodes, spleen, organs
of MALT.
• Adhesion molecules enable selective
attachment of various types of
lymphocytes.
Circulation of Lymphocytes in the body
The role of High Endotelial Venules
Roitt/Broskoff/Male: IMMUNOLOGy, 4th ed