Week 2 Immunology Dr. Lydia Medeiros Food Safety and High-Risk Groups.

Week 2Immunology

Dr. Lydia Medeiros

Food Safety and High-Risk Groups

Vocabulary of the Immune System

Handout #1

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The Immune System

• Innate or Natural Immunity (vertebrates/invertebrates)– Nonspecific response– Immediate response– Short-term response

• Adaptive or Acquired Immunity (vertebrates)– Specific response– Slow response– Long-term response

Innate Immunity

• Skin

• Mucosal secretions

• Intestinal pH and digestive enzymes

• Peyer’s Patch in intestine (M cells)

• Reticuloendothelial System

• Involves Natural Killer cells, Complement and Phagocytic cells (neutrophils or macrophages)

The Reticuloendothelial System

• Blood and tissue phagocytic cells (neutrophils and macrophages)

• Lymphoid tissue

• Liver (Kupffer cells)

• Spleen (red pulp)

• Bone marrow

• Lung, lining of the GI tract, urogenital tract

Destruction of Bacteria by Phagocytosis and Complement

Handout #2

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Cells of the Immune System

Handout #3

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Cells of the Immune System

• B-cells– Derived from stem cells in the bone marrow– Late stage or mature B-cells released to

circulation (maturity completed in spleen)– Naïve B-cells encounter antigen via antigen

presenting cells or direct contact– Immune reactions involve lymphatic system,

lymph nodes, and spleen (white pulp)

Cells of the Immune System

• T-Cells– Derived from stem cells in bone marrow– Immature T-cells transport to the thymus– Selectivity against self occurs in thymus– Only about 5% of nascent T-cells survive

maturation in the thymus– Responds to MHC class I and class II

complexes in periphery, especially lymphatic system and lymph nodes

Overview Summary

• First line of defense– Mechanical barriers– Chemical barriers

• Second line of defense– Inflammation response– Phagocytosis

• Third line of defense– Specific immune responses– Natural Killer Cells

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Adaptive Immunity

Adaptive ImmunityAdaptive Immunity

Humoral ImmunityHumoral ImmunityB-cell and antibody B-cell and antibody mediated responsemediated response

Cell Mediated ImmunityCell Mediated Immunity T-cell responseT-cell response

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Adaptive Immunity

• Phagocytic cells (neutophils or macrophages)

• Thymus and lymphoid tissues

• B-cells and T-cells

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Adaptive Immunity

Antibody

A protein that is produced as a result of the introduction of an antigen and has the ability to combine with the antigen that stimulated

its production.

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Adaptive Immunity

Major Histocompatibility Complex (MHC)

A cluster of genes located in close proximity that determine histocompatibility antigens

from members of a species. (eg. recognition of self versus non-self).

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Adaptive Immunity

Cytokine

A factor such as a lymphokine or monokine produced by cells that affect other cells (eg. lymphocytes and

macrophages) and have multiple immunomodulating functions.

Cytokines include interleukins and interferons.

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Adaptive Immunity

• B-cells– naïve cells have not encountered antigen– antibody on cell surface binds antigen– antigen presenting cells – predominately require signal from T-cell for

activation– after activation, plasma cells produce and

secrete antibodies– some B-cells become memory cells

Adaptive Immunity

• T-cells– CD4 T-cells (Helper – TH1 or TH2)

• Recognized MHC class II complexes• TH1 activates macrophages• TH2 activates B-cells

– CD8 T-cells (Cytotoxic or Killer T-cells)• Recognizes MHC class I complexes• Lyses infected cells

The Humoral Immune Response

CD4 Helper CD4 Helper T-cellT-cell

(T(THH2 type)2 type)

PathogenPathogenB-cellB-cell

Cytokine Cytokine release (IL-4 release (IL-4 and 5) from and 5) from helper T cell helper T cell activates B cellactivates B cell

YYYY

T-cell receptor T-cell receptor combines with combines with MHC II complexMHC II complex

B-cell proliferationB-cell proliferation

Memory Memory B-cellB-cell

Plasma Plasma cellcell

YYYY

YY YY

Antigen presenting cell Antigen presenting cell MHC II complex formedMHC II complex formed

Lymph NodeLymph Node

The Cell-Mediated Immune ResponseThe Cell-Mediated Immune Response

Antigen Antigen Presenting Presenting CellCell

CD4 Helper CD4 Helper T-cellT-cell

(T(THH1 type)1 type)

PathogenPathogen CD8 CD8 Cytotoxic Cytotoxic

T-cellT-cell

Cytokine release Cytokine release and interaction and interaction with CD8 cellswith CD8 cells

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How do foodborne pathogens invade the human body?

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Viral InfectionsNorovirus and Hepatitis A

VirusVirus

Antigen Presenting CellAntigen Presenting Cell

عع

Virus produces proteinVirus produces protein

Protein/MHC class I Protein/MHC class I complex formscomplex forms

CD8 Cytoxic T-CD8 Cytoxic T-cell responds to cell responds to MHC class I MHC class I complexcomplex

Natural Natural Killer cellKiller cell

Parasitic InfectionParasitic InfectionToxoplasmosis gondiiToxoplasmosis gondii

Tissue cellTissue cell

ParasiteParasite

Parasitic InfectionParasitic InfectionToxoplasmosis gondii Toxoplasmosis gondii

Cryptosporidium parvum ???Cryptosporidium parvum ???

MacrophageMacrophage

CD4 Helper CD4 Helper T-cell T-cell

(T(THH1 type)1 type)

ParasiteParasite CD8 CD8 Cytotoxic Cytotoxic

T-cellT-cell

Cytokine release Cytokine release and interaction and interaction with CD8 cellswith CD8 cells

YY

YYYY

YY

Bacterial Intoxications (Exotoxin)Staphylococcus aureus

Antigen Antigen Presenting Presenting

CellCell

CD4 CD4 T-cellT-cell

Bacterial Bacterial exotoxin acts as exotoxin acts as SuperantigenSuperantigen

Massive Massive cytokine cytokine releaserelease

Massive Massive cytokine cytokine releaserelease

Ineffective Ineffective CD4 T-cellCD4 T-cell

Ineffective Ineffective CD4 T-cellCD4 T-cell

Ineffective Ineffective CD4 T-cellCD4 T-cell Ineffective Ineffective

CD4 T-cellCD4 T-cell

Systemic Toxicity – Virulence factorSystemic Toxicity – Virulence factor

Supressed Immune ResponseSupressed Immune Response

Human Host Becomes SickerHuman Host Becomes Sicker

Bacterial InfectionBacterial InfectionListeria monocytogenesListeria monocytogenes

MacrophageMacrophage

MacrophageMacrophage

ListeriaListeria

Listeria infects Listeria infects another macrophageanother macrophage

No Immune No Immune ResponseResponse

Bacterial InfectionBacterial InfectionListeria, Campylobacter, V. parahaemolyticus, YersiniaListeria, Campylobacter, V. parahaemolyticus, Yersinia

Antigen Antigen Presenting Presenting CellCell

CD4 Helper CD4 Helper T-cellT-cell

(T(THH1 type)1 type)

PathogenPathogen CD8 CD8 Cytotoxic Cytotoxic

T-cellT-cell

Cytokine release Cytokine release and interaction and interaction with CD8 cellswith CD8 cells

Toxin-Mediated InfectionsSalmonella, Shigella, E. coli O157,

C. perfringens, B. cereus

• Toxin– Produced systemically or intra-luminally– Toxin neutralized by antibodies and

complement

• Infective cells– Neutralized by immune response

Toxin-mediated Infection

Bacteria Bacteria growgrow

Produce Produce toxintoxin

YY

YY

YY

YY

YY

YYCC

CC

CC

CCCC

CC

CC

YY

YY

Toxin opsonized Toxin opsonized by antibody and by antibody and

complementcomplement

Phagocytosis Phagocytosis by APCby APC

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The Immune System and Groups at High Risk for

Foodborne Illness

Infants and Young Children

Pregnancy

Seniors

Immune Compromised

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Infants and Young Children

• Immune defect– Immature immune system response– Lower infective dose

Pregnancy

• Immune Defect– Hormonal suppression of cell-mediated

immunity– Switch from TH1 or TH2 T-cell type that

favors antibody response– Listeria and Toxoplasmosis response

specific for TH1 type T-cells

Listeria : Mode of InfectionListeria : Mode of InfectionPregnancyPregnancy

ListeriaListeria

Helper T-cellHelper T-cell

(Th-2 type)(Th-2 type)

Humoral Immune Humoral Immune ResponseResponse

(Antibodies Produced)(Antibodies Produced)

Listeria infects Listeria infects another another macrophagemacrophage

The Elderly

• Immune Defect– Decrease stomach acidity naturally– Increased use of anti-acid, anti-inflammatory or

steroid medications– Decline in immune system response due to

aging – Nutritional influence on immune response– Greater chance for exacerbating acute or

chronic disease

Immune Compromised StatusPharmacological

Immune defect• Cancer - Loss of immune response efficiency due to

disease or medical therapy

• Bone marrow transplant – Major reduction of immune system function due to absence and function of bone marrow

• Solid organ transplant – Mild suppression due to life-long use of immune suppressant drugs to prevent graft rejection.

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