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Immune Response and Lymphoid
Organs
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Immune System
- System of cells that has the ability to
distinguish self from non-self.
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Cells of the Immune System
Distributed throughout the body
Arranged in small spherical nodules (lymphoid
nodules)
Organized in larger lymphoid organs (lymphnodes, spleen, thymus, bone marrow)
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Lymphoid nodules are found:
o Mucosa of the digestive systemo tonsils,
o Peyers patches
o Appendixo Respiratory system
o Reproductive system
o Urinary system (MALT) mucosa-associatedlymphoid tissue
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AntigenAntigen Non-self
Elicit immune response
Foreign material
Soluble molecules such as CHON,
polysaccharides, & nucleoproteins
Molecules belonging to bacteria, protozoa,
tumor cells, or virus-infected cells. Has antigenic determinantsor epitopes
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AntibodyAntibody a.k.a. Immunoglobulin
Glycoprotein in nature
Secreted by Plasma cells
IgM, IgA, IgG, IgE, & IgG
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q Chainsq Heavy chains (H) 2 identical
q Light chains (L) 2 identical
q Fragmentsq Antibody Binding Fragment (Fab)
q Cystallizable Fragment (Fc)
q Regionsq Variable Region (V)
q Constant Region (C)
q Domains (Ig domains)q V
Lq C Lq VHq CH1
q CH2
q CH3
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CytokinesCytokines Molecule regulator for immune cells functions
8 to 80 kDa
Influence by cellular and humoral immune response
Acts on cells that have receptor for them Produced by lymphocytes, macrophages & other
leukocytes.
Chemotaxinsor chemokines cytokines that induce
diapedesis of leukocytes & migration to inflammedsites.
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Cells of the Immune System
Cells involved Lymphocytes,
Plasma cells
Mast cells Neutrophils
Eosinophils
APC(Antigen Presenting Cells)
Macrophage Dendritic Cells
Lympocytes
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LymphocytesLymphocytes
Classified as
B lymphocytes
T lymphocytes Natural Killer Cells
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B and T lymphocytesB and T lymphocytes
B LymphocytesB Lymphocytes
Surface Marker
- Monomeric Igm
Plasma Cell
Memory B Cell
T LymphocytesT Lymphocytes
65-75% circulating lymphocytes
TCR (T cell receptor)
Recognize only epitopes
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T cells subpopulationT cells subpopulation
Helper CellsHelper Cells
- CD4
- promote B cell differentiation
- activate macrophages
CytotoxicCytotoxicT cellsT cells
- CD8
- perforins
- apoptosis
Regulatory T cellsRegulatory T cells-- CD24 and CD25
-- Immune tolerance
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MajorMajor HistocompatibilityHistocompatibility Complex (MHC) &Complex (MHC) &Antigen PresentationAntigen Presentation
MHC
- complex of choromosomal loci encoding
several proteins known as class I and class IIMHC molecules.
MHC I
- nucleated
MHC II
- APCs
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Antigen Presenting CellsAntigen Presenting Cells
Class II MHC molecules
Macrophage, dedritic cells, B cells, langerhans cells
Recognized by helper cells
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Types of Immune ResponseTypes of Immune Response
Two Basic Types
Innate response
Adaptive response
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Lymphoid Tissue
Connective tissue rich with lymphocytes
H&E-stained sections (dark blue)
Free cells, rich network of reticular fibers oftype III collagen supporting the cells.
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Lymphoid NodulesLymphoid Nodules
lymphocytes in spherical masses, B Lymphocytes
lymph nodes, spleen, tonsils
Free lymphoid nodules are present in connective
tissue of mucosal linings, where together with free
lymphocytes, they constitute the MALT (mucosa-associated lymphoid tissue)
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ThymusThymus
Bilateral organ located in mediastinum, peak
development during youth.
central or primary lymphoid organ
T lymphocytes
precursor is lymphoblast originated from bonemarrow
medulla and cortex
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Epithelial reticular cells extend long processes bound together by
desmosomes to make the framework for the lymphocytes. The epithelial
reticular cells also secrete polypeptide factors that promote T cell
maturation.
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Role of Thymus in T Cell MaturationRole of Thymus in T Cell Maturation
Central self-tolerance induction
Nave T lymphoblast
- T cell receptor, CD4 or CD8
Progenitor arise from fetal liver, or bone marrow & migrate to
the thymus.
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MucosaMucosa--Associated Lymphoid Tissue (MALT)Associated Lymphoid Tissue (MALT)
Digestive, respiratory, genitourinary tracts are common sites
One of the largest organs.
- tonsils (according to location; palatine, pharyngeal, lingual
tonsils) appendix, Peyers patches in the ileum.
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Lymph NodesLymph Nodes
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Most common cells of lymph nodes are
lymphocytes, macrophages, & other APCs,plasma cells, & reticular cells; follicular
dendritic cells
The different arrangement of the cells and of
the reticular fiber stroma supporting the cells
creates a cortex, a medulla, and an
intervening paracortex
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ParacortexParacortex
- Do not have precise boundaries.
- Distinguishable due to lack of B cell lymphoid
nodules.
- Venules in the paracortex comprise an important
entry points for lymphocytes moving from blood intolymph nodes.
- Lymph node medulla components:
- Medullary cords
- Medullary sinuses
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Spleen
q largest single accumulation of lymphoid
tissue in the body and only one involved in
blood filtration
q important organ in defense against blood-
borne pathogens.
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SplenicSplenicPulpPulp
Two components:- white pulp
consist of lymphoid nodules & periarteriolar
lymphoid sheathes
- Red pulpblood filled sinusoids and splenic cords (Bilroth)
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