Immune Response and Lymphoid Organs

8/9/2019 Immune Response and Lymphoid Organs

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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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Immune Response and Lymphoid Organs

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