Nonspecific Host Defense Mechanisms

Host Defense Mechanisms

Ways in which the body protects itself from pathogens

There are 3 lines of defense.The first two lines of defense are nonspecific.

The body’s way of destroying all foreign substances that enter including pathogens

The third line of defense is specific. Antibodies are produced in response to an

antigen.

First Line of DefenseSkin

Serves as a physical barrier to pathogensFew microbes can penetrate intact skin

Mucous MembranesAlthough they are only one cell layer thick,

they are a physical barrier to pathogens.Goblet cells produce mucus that entrap

pathogens and prevent them from causing infection.

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What are some chemical and cellular examples for

the first line of defense?

•Regarding the skin?•Mucous membrane cells?•Digestive tract?

First Line of DefenseMicrobial Antagonism

When the presence of the normal flora prevents colonization of pathogens

This may happen because of: Competition for colonization sites Competition for nutrients Production of substances that kill other bacteria

Second Line of DefenseIf pathogens get passed the first line of

defense, they are usually destroyed by the second line of defense.

These involve chemical and cellular reactions by the body, which result in:FeverProduction of interferonsActivation of the complement systemInflammationChemotaxisPhagocytosis

TransferrinA protein that is made in the liver and has a

high affinity for iron.Its role in the body is to store and deliver iron

to host cells. During an infection, its production is greatly

increased in the body.Binds to the iron present so that other

microbes cannot use this essential nutrient

Fever Increase in normal body temperature (above

100°F)Pyrogens stimulate the production of a fever.

May originate from outside (i.e. pathogens) or inside the body (i.e. Interleukin 1 – IL-1)

Helps body in following ways:Stimulates white blood cells (leukocytes) to go

and destroy invadersReduces free plasma ironInduces the production of IL-1 that results in

the activation of leukocytes in the immune response

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Interferons Small, antiviral proteins produced by virus-

infected cellsAttach to other host cells to prevent further

viral replication“interfere” with viral replicationLimits spread of disease so that other

responses may help fight pathogens

The Complement SystemInvolves about 30 proteins found in normal

blood plasma that interact together in response to the presence of a foreign substance

Results in a complex stepwise reaction called the complement cascade

Which results in:Attraction of phagocytes to sites where they

are neededActivation of leukocytesLysis of bacteria and other foreign cellsIncreased phagocytosis

Acute-Phase ProteinsProteins found in blood plasma that greatly

increase in response to infection, inflammation, and tissue injury

Help to prevent infection and promote tissue repair

Example : C-reactive proteinWhich is used as a marker for inflammation

CytokinesChemical mediators that are released from

many different types of cells in the human body.

Help cells to communicate with each otherAid in communication within the immune

system and between the immune system and other systems

If another type of cell has the right receptors, it can recognize the presence of cytokines.

Inflammation Occurs as a result of an injury, irritation,

microbial invasion, or bacterial toxin4 signs of inflammation:

Redness, heat, swelling, painResults in a cascade of events that work to:

Localize an infectionPrevent the spread of microbial invadersNeutralize any toxins being produced at the

siteAid in the repair of damaged tissue

Inflammation Vasodilation (increase in the diameter of

capillaries), which increases blood flow to the siteResults in redness and heat

Increased permeability of capillaries, allowing the escape of plasma and plasma proteinsCauses edema (swelling)

Exit of leukocytes from the capillaries and their accumulation at the site of injuryInjury or infection attracts chemotactic agents

which in turn attract leukocytes

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om

Phagocytosis The process by which phagocytes surround

and engulf foreign materialPhagocytes – phagocytic white blood cells

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Cellular Elements of the Blood

Erythrocytes (red blood cells)Thrombocytes (platelets)Leukocytes (white blood cells)

Granulocytes Basophils Eosinophils - Phagocytic Neutrophils - Phagocytic

Monocytes/Macrophages - PhagocyticLymphocytes

B cells T cells Natural killer cells

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4 Steps in Phagocytosis 1. Chemotaxis

Phagocytes are attracted by chemotactic agents to the site where they are needed.

2. AttachmentPhagocyte attaches to an object.

3. IngestionPseudopodia surround the object, and it is taken

into the cell.4. Digestion

The object is broken down and dissolved by digestive enzymes and other mechanisms.

Phagocytosis

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The End