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Natural resistance or Species resistance is due to?

Physiological processes of humans that are incompatible with those of the pathogen
– Correct chemical receptors not present on human cells
– Conditions may be incompatible for pathogen’s survival


Innate Immunity is?
Adaptive Immunity is?

Innate Immunity: First Line of defense (lack specificity and
memory) no need for activation, always present.
• Adaptive Immunity (Memory and specificity) needs


The Role of Skin in Innate Immunity

– Skin composed of two major layers
– Epidermis
* Multiple layers of tightly packed cells
* Few pathogens can penetrate these layers
* Shedding of dead skin cells removes microorganisms
* Epidermal dendritic cells phagocytize pathogens
– Dermis
* Collagen fibers help skin resist abrasions


The Role of Skin in Innate Immunity: Skin has chemicals that defend against pathogens

1) Perspiration secreted by sweat glands
* Salt inhibits pathogen growth
* Antimicrobial peptides
* Lysozyme destroys cell wall of bacteria
2) Sebum secreted by sebaceous (oil) glands
* Helps keep skin pliable
* Lowers skin pH to a level inhibitory to many bacteria


The Role of Mucous Membranes in Innate Immunity

– Mucous membranes line all body cavities open to
– Two distinct layers
1) Epithelium
– Thin outer covering of the mucous membranes
– Epithelial cells are living
– Tightly packed to prevent entry of pathogens
– Continual shedding of cells carries away microorganisms
2) Deeper connective layer that supports the epithelium


The Role of Normal Microbiota in Innate Immunity

– Microbial antagonism
* Normal microbiota compete with potential
– Normal microbiota make it hard for pathogens to
– Consume nutrients
– Create an environment unfavorable to other
– Help stimulate the body’s second line of defense
– Promote overall health by providing vitamins to host


Defense Components of Blood

– Plasma
* Mostly water containing electrolytes, dissolved gases, nutrients, and proteins
* Serum is the fluid remaining when clotting factors are removed
* Includes iron-binding compounds, complement proteins, and antibodies


Defense Components of Blood: Cells and cell fragments in plasma are called formed elements
– Three types of formed elements

1) Erythrocytes
– Carry oxygen and carbon dioxide in the blood
2) Platelets
– Involved in blood clotting
3) Leukocytes
– Involved in defending the body against invaders
– Divided into granulocytes and agranulocytes


Defense Components of Blood
– Granulocytes
– Neutrophils and eosinophils

1) Granulocytes
– Contain large granules that stain different colors
– Three types
* Basophils – stain blue with basic dye methylene blue
* Eosinophils – stain red/orange with acidic dye eosin
* Neutrophils – stain lilac with mix of acidic and basic
2) Neutrophils and eosinophils
– Phagocytize pathogens
– Capable of diapedesis


Defense Components of Blood
– Agranulocytes

– Cytoplasm appears uniform under a light microscope
– Two types
1) Lymphocytes
– Most involved in adaptive immunity
2) Monocytes
– Leave the blood and mature into macrophages


Lab analysis of leukocytes

– Differential white blood cell count can signal signs of disease
– Increased eosinophils indicate allergies or parasitic worm infection
– Bacterial diseases often show increase in leukocytes and neutrophils
– Viral infections show increase in lymphocytes


Describe Phagocytosis

– Cells capable of phagocytosis are called phagocytes
– Phagocytosis is not completely understood
– Can be divided into six stages
1) Chemotaxis
2) Adherence
3) Ingestion
4) Maturation
5) Killing
6) Elimination


Describe Nonphagocytic Killing: Killing by eosinophils

– Attack parasitic helminths by attaching to their surface
– Secrete toxins that weaken or kill the helminth
– Elevated eosinophils often indicative of a helminth
– Eosinophil mitochondrial DNA and proteins form
structure that kills some bacteria


Nonphagocytic Killing: Killing by natural killer (NK) lymphocytes

– Secrete toxins onto surface of virally infected cells and tumors
– Differentiate normal body cells because they have membrane proteins similar to the NK cells


Nonphagocytic Killing – Killing by neutrophils

– Produce chemicals that kill nearby invaders
– Generate extracellular fibers called neutrophil extracellular traps (NETs) that bind to and kill bacteria


Nonspecific Chemical Defenses Against Pathogens

– Toll-like receptors (TLRs)
– Integral membrane proteins produced by phagocytic
– Bind pathogen-associated molecular patterns
– Initiate defensive responses
– Apoptosis
– Secretion of inflammatory mediators
– Production of stimulants of adaptive immune response
– NOD proteins
– Cytosolic proteins that bind PAMPs


Nonspecific Chemical Defenses Against Pathogens: Interferons

– Released by host cells to nonspecifically inhibit the
spread of viral infections
– Cause many symptoms associated with viral infections
– Two types
1) Types I (alpha and beta)
2) Type II (gamma)


Nonspecific Chemical Defenses Against Pathogens
– Complement

– Set of serum proteins designated numerically according to their order of discovery
– Complement activation results in lysis of the foreign cell
– Complement can be activated in three ways
1) Classical pathway
2) Alternative pathway
3) Lectin pathway


What happens in Complement: Inactivation of complement

Body’s own cells withstand complement cascade
– Proteins on many cells bind and break down activated complement proteins


Inflammation is?

– Nonspecific response to tissue damage from various causes
– Characterized by redness, heat, swelling, and pain
– Two types
1) Acute
2) Long-lasting (chronic)


Acute inflammation is?

– Develops quickly and is short lived
– Is typically beneficial
– Is important in the second line of defense
– Dilation and increased permeability of the blood vessels
– Migration of phagocytes
– Tissue repair


Fever is

– A body temperature over 37°C
– Results when pyrogens trigger the hypothalamus to increase the body’s core temperature
– Various types of pyrogens
– Bacterial toxins
– Cytoplasmic contents of bacteria released by lysis
– Antibody-antigen complexes


Explain the production of fever in response to infection

1) Chemicals secreted by phagocytes travel in blood to hypothalamus
2) Hypothalamus secretes prostaglandin, which resets hypothalamic thermostat
3) Nerve impulses cause shivering, higher metabolic rate, inhibition of sweating, and vasoconstriction
4) These processes increase body temperature to the point set by the hypothalamic thermostat


What are the body's first line and second line of defense?

First line of defense
1) Skin
2) Mucous membranes
3) Normal microbiota
Second line of defense
1) Blood
2) Phagocytosis
3) Non-phagocytic killing
4) Non specific chemical defenses against pathogens
5) Inflammation
6) Fever


Antimicrobial substances: Both skin and mucous membranes are protected by a variety of antimicrobial substances including?

1) Lysozyme
- Enzymes that degrade peptidoglycan
- Found in tears, saliva, blood and phagocytes
2) Peroxidase
- Found in saliva, body tissues, & phagocytes
- breaks down hydrogen peroxide to produce reactive oxygen
3) Lactoferrin
- Sequesters iron from microorganisms (iron essential for microbial growth)
- Found in saliva, some phagocytes, blood & tissue fluids
4) Defensins
- Antimicrobial peptides inserted into microbial membrane
- Found on mucous membranes and phagocytes


WBC's leukocytes are divided into 4 categories

1) Granulocytes
2) Dendritic cells
3) Mononuclear phagocytes (involved in diff. modality of host defense
4) Lymphocytes


Cells of the immune system are?

Always found in normal blood
- numbers increase during infection
- some cells play dual roles in both innate and adaptive immunity
- Blood cell formation called hematopoiesis
* blood cells including immune cells originate from hematopoietic stem cells in bone marrow
* blood cells stimulate to differentiate by colony- stimulating factor


Cells of the innate immune system

Dendritic cell


Soluble factors of innate immune system




- Contain cytoplasmic granules
- Divided into 3 types
1) Neutrophils
2) Basophils
3) Eosinophils