BODY DEFENSE SYSTEM

animal/human must defend , against intruders;-pathogen…??..bacteria, virus, fungi, pathogen from air, water, food, environment….

Body defense system/immunity?

DEFINITION:

ability of an organism to recognize and defend itself against pathogen resisting the attack of many dangerous organisms.

Chapter 1:Body defense system

Chapter 2Innate Host Defenses

IMMUNOLOGY

Body defense system

Innate immunity

External

Physical mechanical

Internal

CellularImmune response

Biological

Molecular

Adaptive /acquired immunity

* DEFINITION: Innate and Adaptive immunity

Host defenses that produce resistance against infection can be adaptive or innate

*Innate defenses: those that act against any type of invading agent

*Adaptive defenses: respond to particular agents called antigens (e.g. viruses and pathogenic bacteria)

Only when our resistance fails do we become susceptible to infection by pathogens

*Adaptive Defenses

*Respond to antigens by producing protein antibodies

*Also involve the activation of the lymphocytes

*Lymphocytes: specific cells of the body’s immune system

*Antibody and cellular responses are more effective against succeeding invasions by same pathogen than against initial invasions

*Innate Defenses1. Physical barriers

2. Chemical barriers

3. Mechanical Barrier

4. Cellular Barrier

5. Inflammation

6. Fever

7. Molecular defenses

*Comparison between innate immunity and adaptive immunity

INNATE IMMUNITY ADAPTIVE IMMUNITY

Non specific- acts against many organism

Specific- respond to the specific antigen

Present from birth Acquired- usually by having disease/ vaccination

Heredity not

Does not become more efficient after more exposure

The immune system efficiency increased and memorized after exposure

Various types of defense mechanism

Involves mostly lymphocytes cell, that produces B cell and T cell

1. Physical Barriers

*Skin and mucous membranes protect your body and internal organs from injury and infectious agents

*These two physical barriers are made of cells that line body surfaces and secrete chemicals

*human beta-defensin-2 on human skin destroys pathogens by poking holes in bacterial membranes

*Mucosa covers those tissues and organs of body cavity exposed to exterior

2. Chemical Barriers

*High salt content of sweat inhibits bacteria from growing

*Sweat and sebum produced by sebaceous glands have low pH that inhibits growth of bacteria

*Acidic pH of stomach is a defense against intestinal pathogens

*Lysozyme: present in tears, saliva, and mucus, cleaves peptidoglycan linkage in bacterial cell wall

3. MECHANICAL BARRIER

FUNCTION:- PREVENT/FLUSH INVADING MICROBES IN DIFFERENT TYPE OF MECHANICAL WAY

•Hair and mucus- nasal, respirotary system•Coughing and sneezing•Urinary flow- remove microbes in urinary

tract• Tears and saliva – flush bacteria from

eyes and mouth•Vomitting and diarrhea- flush bacteria

from digestive tract

4. Cellular Defenses – Defensive Cells

*Blood consists of about 60% liquid called plasma and 40% formed elements (cells)

*Formed elements: erthyrocytes, platelets, and leukocytes

*Leukocytes are defensive cells important to adaptive and innate host defenses

Formed cellular elements of the blood

*Granulocytes

* Have granular cytoplasm and an irregularly shaped, lobed nucleus

* Include:1. Mast cells: prevalent in connective tissue,

release histamine, and associated with allergies2. Basophils: release histamine which helps

initiate inflammatory response3. Eosinophils: present in large numbers during

allergic reactions4. Neutrophils (polymorphonuclear

leukocytes): phagocytic cells that guard skin/mucous membranes against infection

5. Dendritic cells: phagocytic cells that resemble nerve cells

* Agranulocytes

* Lack granular cytoplasm with round nuclei

* Include:1. Monocytes: phagocytic cells derived

from myeloid stem cells2. Lymphocytes: derived from lymphoid

stem cells and contribute to adaptive host immunity

* Lymphocytes circulate in blood and are found in lymph nodes, spleen, thymus and tonsils

*Phagocytes

*Cells that literally eat or engulf materials*Monocytes, dendritic cell, neutrophils, eosinophils, *Patrol, or circulate through body, destroying dead cells and cellular debris*Guard the skin/mucous membranes against invasion by microorganisms*Macrophages(formed from monocytes): “big eaters” that destroy not only microorganisms but also larger particles

* The Process of Phagocytosis

* Phagocytes digest and destroy invading microbes and foreign particles by a process called phagocytosis

* Phagocytic cells must:

Find Adhere to Ingest

Digest the microorganisms

Phagocytosis of two bacterial cells by a neutrophil

* Chemotaxis

*Phagocytes in tissues first must recognize invading microorganisms

*pattern recognition receptors (PRRs) on the phagocytic cells recognize molecular patterns unique to pathogen

*Phagocytes release cytokines that have specific roles in host defenses

*Chemokines: -A class of cytokines that attract additional phagocytes to site of infection

*Adherence and Ingestion

*The ability of the phagocyte cell membrane to bind to specific molecules on the surface of the microbe is called adherence

*Antiphagocytic capsule: the most common means by which bacteria avoid phagocytosis

*Complement system: coat microbes with antibodies to aid phagocyte in adherence

*Phagosome: pseudopodia fuse and enclose microorganism within this cytoplasmic vacuole

* Digestion

* Phagocytic cells have several mechanisms for digesting and destroying ingested microbes

* Phagolysosome: lysosomes with digestive enzymes fuse with phagosome membrane

* Macrophages use other metabolic products to kill ingested microbes:

1. Oxygen to form hydrogen peroxide2. Nitric oxide and superoxide ions

*Extracellular killing

*What if the intruder is larger than the Macrophage/neutrophils?

The killing need to be done extracellularlly by…Eosinophils- excreting toxic enzymes (MBP) –kill worm Natural killer cell- secrete cytotoxic proteins that kill

intracellular

* Complement

* Refers to a set of more than 20 large regulatory proteins that play a key role in host defense

* General functions of the complement system are:

1. Enhance phagocytosis2. Lyse pathogens directly3. Generate peptide fragments that

regulate inflammation and immune responses

* Works as a cascade: a set of reactions that amplify some effect

5. Inflammation

* The body’s defensive response to tissue damage from microbial infection

* Characterized by signs:1. an increase in temperature2. redness3. swelling4. pain at infected or injured site

Steps in the process of inflammation and subsequent healing

6. Fever

• The elevation of body temperature to kill invading agents and/or inactivate their toxic products

HOW?Raises temperature above opt. temp. of

pathogensMicrobial enzymes or toxins is inactivatedIncrease immune responsePhagocytosis is enhancedAntiviral interferon production is increasedFever makes patient lie to rest..Increased breakdown of lysosomes causing death

of infected cell and microbes.

7. Molecular Defenses

*Involve the action of interferon and complement

*Interferon: interfered with viral replication in other cells

*Humans have three groups of interferon (alpha, beta, and gamma)

*Antiviral enzymes

The mechanism by which interferons alpha and beta act

A Summary of the body’s nonspecific defenses