IMMUNITY

DR. JUNEEM K M DEPARTMENT OF ORAL PATHOLOGY

CONTENTS

• INTRODUCTION• TYPES OF IMMUNITY• INNATE IMMUNITY

IMMUNITY :

•Immunity is derived from the latin word “immunis” meaning to be exempted from

•Its the ability of an organism to resist a particular infection or toxin by the action of specific antibodies or sensitized white blood cells.

•The immune system is a system of biological structures and processes within an organism that protects against disease

• The Boy in the Plastic Bubble is a 1976 made-for-TV movie inspired by the lives of David Vetter and Ted DeVita, who lacked effective immune systems.

Invadingmicrobes

(pathogens)

External defenses

SkinMucous membranesSecretions

INNATE IMMUNITYRapid responses to a

broad range of microbes

ACQUIRED IMMUNITYSlower responses to

specific microbes

Internal defenses

Phagocytic cells

Inflammatory response

Humoral response(antibodies)Antimicrobial proteins

Natural killer cells Cell-mediated response(cytotoxiclymphocytes)

Immunity: Two Intrinsic Defense Systems

INNATE (NONSPECIFIC) SYSTEM •responds quickly•no need to decipher pathogen’s identiy

• Always present in the body

• consists of:

▫First line of defense – intact skin and mucosae prevent entry of microorganisms

• Physical barriers- skin- mucus membrane

- mucus - hair

- stream of tears - urine

- defecation

• Chemical barriers– pH (skin ,stomach, vagina)– sebum– enzymes (stomach, tears)

Second line of defense –

1. Phagocytes

2. natural killer (NK) cells

3. Inflammatory response enlists macrophages, mast cells, WBCs, and chemicals

4. Antimicrobial proteins in blood and tissue fluid

1. Phagocytes

• Macrophages are the chief phagocytic cells

• Free macrophages wander throughout a region in search of cellular debris

• Kupffer cells (liver) and microglia (brain) are fixed macrophages

• Neutrophils become phagocytic when encountering infectious material

• Eosinophils are weakly phagocytic against parasitic worms

• Mast cells bind and ingest a wide range of bacteria

Phagocytic Mobilization

•Occurs in four main phases:

LEUKOCYTOSIS MARGINATION

DIAPEDESIS

CHEMOTAXIS

Inflammatory Response: Phagocytic Mobilization

Neutrophils enter blood from bone marrow

1

2

3

4

Margination

Diapedesis

Positivechemotaxis

Capillary wallEndothelium

Basal lamina

Inflammatory chemicals diffusing from the inflamed site act as chemotactic agents

3

MECHANISM OF PHAGOCYTOSIS

2.Defense by NK cells

• NK cells or natural killer cells

• Have ability to kill a wide variety of microorganisms and tumour cells

• Unlike B and T cells they lack specific surface antigen receptors.

• Present in spleen, lymph nodes , bone marrow and blood

•They kill microbes by the following mechansims:

1. Osmotic lysis by incorporating perforins into the surface of the microbes

2. Release interferons that activate phagocytosis and immunity

3. Inflammation: Tissue Response to Injury•The inflammatory response is

triggered whenever body tissues are injured ▫Prevents the spread of damaging

agents to nearby tissues▫Disposes of cell debris and pathogens▫Sets the stage for repair processes

• The four cardinal signs of acute inflammation are

1. redness ( RUBOR)2. heat (CALOR)3. swelling (TUMOR)4. pain (DOLOR)5. Functiolesia

3 stages of inflammation

• 1. VASODILATION AND INCREASED PERMEABILITY

• 2. PHAGOCYTE MIGRATION AND PHAGOCYTOSIS

• 3. TISSUE REPAIR

•Major events in the local inflammatory response

Figure 43.6

Pathogen Pin

Macrophage

Chemical signals

CapillaryPhagocytic cells

Red blood cell

Bloodclottingelements

Blood clot

Phagocytosis

Fluid, antimicrobial proteins, and clotting elements move from the blood to the site.Clotting begins.

2Chemical signals released by activated macrophages and mast cells at the injury site cause nearby capillaries to widen and become more permeable.

1 Chemokines released by various kinds of cells attract more phagocytic cells from the bloodto the injury site.

3 Neutrophils and macrophagesphagocytose pathogens and cell debris at the site, and the tissue heals.

4

4. Antimicrobial Proteins

•Enhance the innate defenses by:

Attacking microorganisms directlyHindering microorganisms’ ability to

reproduce

•The most important antimicrobial proteins are:▫Interferon▫Complement proteins

4 a. Interferon (IFN)

•Genes that synthesize IFN are activated when a host cell is invaded by a virus

•Interferon molecules leave the infected cell and enter neighboring cellsInterferon stimulates the neighboring cells

to activate genes for PKR (an antiviral protein)PKR nonspecifically blocks viral reproduction

in the neighboring cell

Interferon Family•Interferons are a family of related

proteins each with slightly different physiological effects

•Lymphocytes secrete gamma () interferon, but most other WBCs secrete alpha () interferon

•Fibroblasts secrete beta () interferon

•Interferons also activate macrophages and mobilize NKs

4 b. Complement

•20 or so proteins that circulate in the blood in an inactive form

•Proteins include C1 through C9, factors B, D, and P, and regulatory proteins

•Provides a major mechanism for destroying foreign substances in the body

Complement Pathways

•Complement can be activated by two pathways: classical and alternative

•Each pathway involves a cascade in which complement proteins are activated in an orderly sequence and where each step catalyzes the next

Complement Pathways

REFERENCE:

1. Guyton And Hall Textbook Of Medical Physiology, 12th Edition

2. Textbook Of Medical Physiology , 2nd Edition, Prof. GK Pal

3. Textbook Of Microbiology, 8th Edition; Ananthnarayan And Paniker

4. Essential Pathology For Dental Students , 3rd Edition; Harsh Mohan