Prim a r y lymphoid organs : - Bone marrow - Thymus the cells of the immune system originate in and mature here Secondary lymphoid organs: - Spleen - Lymphatic vessels - Lymph nodes - Adenoids and tonsils - MALT (Mucosal Associated Lymphoid Tissue) GALT (Gut Associated Lymphoid Tissue) BALT (Bronchus Associated Lymphoid Tissue) SALT (Skin Associated Lymphoid Tissue) NALT (Nasal Associated Lymphoid Tissue) not for cell development. (final differentiation, activation may be performed) The cells of the adaptive immune system recognize here the pathogens LYMPHOID ORGANS ! !
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Primary lymphoid organs : - Bone marrow - Thymus the cells of the immune system originate in and mature here Secondary lymphoid organs: - Spleen - Lymphatic.
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Primary lymphoid organs:
- Bone marrow- Thymus
the cells of the immune system originate in and mature here
not for cell development. (final differentiation, activation may be performed) The cells of the adaptive immune system recognize
here the pathogens
LYMPHOID ORGANS!!
THE TWO ARMS OF THE IMMUNE SYSTEM
Monocytes, Macrophages, Dendritic cells, Granulocytes, NK cells and Complement components
B and T cellsMonocytes, Macrophages, Dendritic cells, Granulocytes, NK cells and Complement components
!!
MEMORY
Professional phagocytic cellsmacrophagesneutrophyl granulocytesdendrtitic cells
Professional antigen presenting cellsmacrophagesB lymphocytesdendrtitic cells
they express MHCII molecules
the protein degradation products (peptides) can be presented to T lymphocytes by MHC molecules
!!
!!
Cells of innate immune system:
Macrophages: Macrophages are constitutively present in tissues and recognize microbes that enter these
tissues and respond rapidly to these microbes. Initiate the immune response• These cells are phagocytes (eliminate the pathogens)• Activate the innate immune response (by secreted proteins, called cytokines)• Activate the adaptive immune system. Macrophages serve as APCs that display antigens to
and activate T lymphocytes
• Dendritic cellsare constitutively present in tissues and recognize rapidly microbes that enter these tissues. Initiate the immune response.• They have phagocytic capabilities migrate to lymph nodes, and display microbial antigens to T lymphocytes,professional antigen presentimg cells (APC)
Neutrophil granulocytesare phagocytes, the main function to eliminate the pathogensAppear only in the circulation under normal conditionMain actors In inflammatory processes
!!
Recognition is inevitable
Innate immunity as a first line of defence
Innate immune cells recognize frequently found structures of pathogens by PRRs ,
PRRs (pattern recognition receptors) are responsible for recognize conserved structures of the microbes
Danger signal!The innate immune system also recognizes molecules that are released from damaged or necrotic cells. Such molecules are called damage-associated molecular patterns (DAMPs).
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OPSONIZATION ! !
Main opsonins:antibodiesComplement fragmentsAcute-phase proteins
Opsonization facilitate and accelerate the recognition of the pathogen by phaogocytes,opsonins form a bridge between pathogen and a phagocyte connecting them.
direct connetion between innate cells
and pathogen)(
Specificity of innate immunity
Few receptors (20-30) are responsible for the recognition of all the pathogens
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:• membrane-bound heterodimer composed of an α chain and a β chain, each chain
containing one variable (V) region and one constant (C) region Both the α chain and the β chain of the TCR participate in specific recognition of MHC molecules and bound peptides
! T cell receptor (TCR) The TCR, which recognizes peptide antigens displayed by MHC molecules!
BCR
TCR
!!
B cell Plasma cell
TCRs only function as membrane receptors
T cell
ANTIGEN RECOGNITION BY T-CELLS REQUIRESPEPTIDE ANTIGENS AND ANTIGEN PRESENTING CELLS
THAT EXPRESS MHC MOLECULES
IIT
No T-cell response
soluble Ag
Native membrane Ag
Peptide antigen
Cell surface MHC-peptide complex
T-cell response
Cell surfacepeptides APC
!!
APCAPC
PEPTIDE
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2m
STRUCTURE OF CLASS I MHC MOLECULES
MHCI
Expressed by all nucleated cells
!!
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PEPTIDE
STRUCTURE OF CLASS II MHC MOLECULES
MHCII
Expressed by professional antigen presenting cellsMacrophage, dendritic cell, B cell
!!
ANTIGEN RECOGNITION BY T-CELLS REQUIRESPEPTIDE ANTIGENS AND ANTIGEN PRESENTING CELLS
THAT EXPRESS MHC MOLECULES
IIT
No T-cell response
soluble Ag
Native membrane Ag
Peptide antigen
Cell surface MHC-peptide complex
T-cell response
Cell surfacepeptides APC
!!
APCAPC
MHCI
Displays intracellular antigensto cytotoxic T cells
!!
MHCII
Displays extracellular antigensto helper T cells
!!
Peptides of endogenous proteins (virus, tumor) bind to class I MHC
molecules presented to cytotoxic T cells
Tc
Endogenous Ag
RECOGNITION OF EXOGENOUS AND ENDOGENOUS ANTIGENES BY T-LYMPHOCYTES
Exogenous Ag
Th
Peptides of exogenous proteins (toxin, bacteria, allergen) bind to class II MHC molecules presented to helper T cells
TCR
Peptide
MHCI
TCR
Peptide
MHCII
APC
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!!T cell receptor (TCR) recognizes peptide antigen and
simultaneously also recognizes the MHC molecule that is displaying that peptide