Unit 12: Immunology; Lesson 1: Innate Immunity: Nonspecific Defense Mechanisms

*Define phagocytosis

The ingestion of a microorganism or other substance (such as debris) by a cell -clear away debris- dead body cells, denatured proteins -the means by which cells in human body counter infection as part of 2nd line of defense -Phagocytes -Initially- granulocytes (esp neutrophils) dominate INITIAL PHASE-they are actively phagocytic (increased number in differential WBC count) -infection progresses- MACROPHAGES dominate- phagocytize remaining living bacteria and dead or dying bacteria -increase # of monocytes (develop into macrophages)- reflected in differential WBC count

*Identify the two lines of nonspecific defense, and list their components

-1st line of defense: SKIN and MUCOUS MEMBRANES -2nd line of defense- PHAGOCYTES, INFLAMMATION, FEVER, and ANTIMICROBIAL SUBSTANCES produced by the body.

Cytokines

-Cytokines- proteins that regulate the intensity and duration of immune responses. -A role of cytokines is to ISOLATE and DESTROY the microbes as part of the INFLAMMATORY response. -They also can activate the T and B cells involved in adaptive immunity.

Eosinophils

-stain RED or ORANGE w/ ACIDIC dye eosin -somewhat phagocytic cells -have ability to leave blood -major function: produce toxin proteins against certain PARASITES (HELMINTHS) -too small to ingest and destroy helminths but can attach to outer surface of parasite and discharge peroxide ions that can destroy them -numbers increase during PARASITIC WORM INFECTIONS & HYPERSENSITIVITY (ALLERGY) REACTIONS

Neutrophils

-stain pale LILAC w/ mixture of Acidic & Basic dyes -nuclei-2-5 lobes -highly phagocytic and motile -active in INITIAL STAGE OF INFECTION -have ability to leave blood, enter infectious tissue, and destroy microbes and foreign particles

*Compare resistance and Suceptibility

=Immunity/ Resistance- our ability to ward off diseases caused by microbes or their products and to protect against environmental agents such as pollen, drugs, foods, chemicals, and animal dander -Susceptibility- vulnerability or LACK of immunity

Second Line of Defense

• 1. A microbe's penetration of the first line of defense encourages production of phagocytes, inflammation, fever, and antimicrobial substances.

Formed Elements of Blood

• 1. Blood consists of plasma (fluid) and formed elements (cells and cell fragments). • 2. Leukocytes (white blood cells) are divided into granulocytes (neutrophils, basophils, eosinophils) and agranulocytes. • 3. During many infections, the number of leukocytes increases (leukocytosis); some infections are characterized by leukopenia (decrease in leukocytes).

Chemical Factors

• 1. Fatty acids in sebum and earwax inhibit the growth of pathogenic bacteria. • 2. Perspiration washes microorganisms off the skin. • 3. Lysozyme is found in tears, saliva, nasal secretions, and perspiration. • 4. The high acidity (pH 1.2-3.0) of gastric juice prevents microbial growth in the stomach.

The Concept of Immunity

• 1. Innate immunity refers to all body defenses that protect the body against any kind of pathogen. • 2. Adaptive immunity refers to defenses (antibodies) against specific microorganisms. • 3. Toll-like receptors in plasma membranes of macrophages and dendritic cells bind to invading microbes.

Normal Microbiota and Innate Immunity

• 1. Normal microbiota change the environment, a process that can prevent the growth of pathogens.

Phagocytes

• 1. Phagocytosis is the ingestion of microorganisms or particulate matter by a cell. • 2. Phagocytosis is performed by phagocytes, certain types of white blood cells or their derivatives.

SUMMARY! Introduction

• 1. The ability to ward off disease through body defenses is called immunity. • 2. Lack of immunity is called susceptibility.

First Line of Defense: Skin and Mucous Membranes

• 1. The body's first line of defense against infections is a physical barrier and the nonspecific chemicals of the skin and mucous membranes.

The Lymphatic System

• 1. The lymphatic system consists of lymph vessels, lymph nodes, and lymphoid tissue. • 2. Interstitial fluid is returned to blood plasma via lymph vessels.

*Define nonspecific defense

-Innate immunity- refers to all body defenses that protect the body against ANY kind of pathogen. -defenses that are present at BIRTH -always present and available- provide rapid response to protect usagainst disease -does NOT involve specific recognition of a microbe -does NOT have a memory response -includes First line of defense (skin and mucous membranes) and Second line of defense (natural killer cells and phagocytes, inflammation, fever, antimicrobial substances) -designed to PREVENT MICROBES FROM GAINING ACCESS INTO THEBODY and to help ELIMINATE THOSE THAT DO GAIN ACCESS -responds RAPIDLY by detecting then eliminating -responses- activated by PROTEIN RECEPTORS in the plasma membranes of defensive cells.

other factors that help protect epitheilal surfaces:

-Lacrimal apparatus- washing action of the tears producedby the lacrimal glands pass across surface of eyeball into two small holes that convey the tears into the lacrimal canals and the nasolacrimal duct --saliva- also helps dilute numbers of microbes and wash them from surface of teeth and mucous membrane of the mouth -prevents colonization by microbes

Lymphocytes

-Natural Killer (NK cells), T cells, B cells Natural Killer Cells: -Function: Destroy target cells by CYTOLYSIS and APOPTOSIS -found in blood and in spleen, lymph nodes, red bone marrow -can kill wide variety of infected body cells and certain tumour cells -ATTACK- any body cells that display ABNORMAL or UNUSUAL PLASMA MEMBRANE PROTEINS -Binding of NK cells to target cells- cause release of toxic substances from NK cells- some contain PERFORINS (insert into plasma membrane of target cells- create channels (perforations), extracellular fluid flows into cell, cell bursts (CYTOLYSIS) -Other NK cells- release GRANZYMES- protein digesting enzymes that induce target cell to undergo apoptosis (self destruction) -kills infected cells, but not microbes inside cells -released microbes (which may or may not be intact) can be destroyed by phagocytes

Chemical Factors

-Sebaceous (oil) glands- prevents hairs from drying and becoming brittle -Sebum- forms protective film over surface of skin -contains unsaturated fatty acids- inhibits growth of pathogenic bacteri and fungi -low pH of skin (3-5) caused by secretions of fatty acids and lactic acid --bacteria that live on skin- decompose sloughed-off skin cells- the resultant organic molecules and the end-products of their metabolism produce body odor. -certain bacteria commonly found on skin metabolize sebum- forming free fatty acids that cause inflammatory response associated w/ acne -sweat glands- perspiration- maintains body temp, eliminates wastes, flush microbes from skin surface -perspiration- contains LYSOZYME- breaks down cell walls of gram-POS bacteria (and gram neg to a lesser extent) -breaks chemical bonds of peptidoglycan- destroys cell walls -found in tears, saliva, nasal secretions, tissue fluids, and urine -earwax- chemical protectant -secretions rich in fatty acids (low pH 3-5) inhibits growth of pathogenic microbes -Saliva- Salivary Amylase (digests starch) -also Lysozyme, Urea, Uric Acid -pH- 6.55-6.85- inhibits microbes -contains antibody (immunoglobulin A)- prevents attachment of microbes so they cant penetrate mucous membranes. -Gastric Juice- HCL, Enzymes, and Mucous -High acidity (1.2-3)- destroys bacteria & most bacterial toxins (except Clostridium botulinum & S. aureus) -Vaginal Secretions- glycogen produced by vaginal epithelial cells- broken down into lactic acid by Lactobacillus acidophilus -pH 3-5- inhibtis microbes -Urine- contains lysozyme -pH 6-inhibits microbes

Mucous Membranes

-consist of an epithelial layer and an underlying connective tissue layer -inhibit entrance of microbes -line the GI, respiratory and genitourinary tracts -epithelial layer of a mucous membrane secretes mucus- viscous glycoprotein produced by goblet cells of a mucous membrane -prevents tracts from drying out -some pathogens can thrive on moist secretions of a mucous membrane & are able to penetrate the membrane if the microbe is present in sufficient numbers. -Treponema pallidum-such a pathogen. -penetration may be facilitated by toxic substances produced by the microbe, prior injury by viral infection, or mucosal irritation.

Leukopenia

-decrease in leukocyte count -caused by salmonellosis, brucellosis, some viral and rickettsial infections -count may increase due to meningitis, infectious mononucleosis, appendicitis, pneumonococcal pneumonia, gonorrhea

Dendritic Cells

-derived from monocytes -abundant in epidermis of skin, mucous membranes, thymus and lymph nodes -Function- to DESTROY MICROBES by PHAGOCYTOSIS and to initiate ADAPTIVE IMMUNE RESPONSE

Second Line of Defense

-includes defensive cells: Phagocytic cells-neutrophils, eosinophils, dendritic cells, and macrophages ; Inflammation; Fever; Antimicrobial Substances -Leukocytes- WBCs -divided into 2 main categories: granulocytes and agranulocytse -Granulocytes: -large granules in cytoplasm that can be seen under a light microscope after staining -3 types of cells on basis of how granules stain: -Neutrophils, Basophils, Eosinophils -Agranulocytes -3 diff types: Monocytes, Dendritic Cells and Lymphocytes

Agranulocytes- Macrophages

-mature monocytes -Function in PHAGOCYTOSIS

-Resp and GI tracts- physical forms of defense

-mucus traps microbes that enter -mucous membrane of nose also has mucus coated hairs that filter inhaled air and trap microbes, dust, pollutants -cells of mucous membrane of lower resp tract- covered w/ cilia -cilia- propels inhaled dust and microbes that are trapped in mucus upwards towards throat- called the ciliary escalator -keeps mucus blanket moving toward throat- coughing and sneezing speed it up -microbes are also prevented from resp tract by epiglottis- covers larynx during swallowing. -external ear canal: contains hairs and earwax (cerumen)- prevents microbes, dust, insects and water from entering the ear. -cleansing of urethra by flow or urine (MOVEMENT OUT)- another physical factor- prevents colonization in genitourinary tract -infections of urinary catheters alter urine flow- UTI may develop -vaginal secretions- (MOVEMENT OUT) move microbes out of female body -Peristalsis, defecation, vomiting, diarrhea- expel microbes

Agranulocytes- Monocyte

-not actively phagocytic UNTIL they leave circulating blood, enter body tissues, and mature into MACROPHAGES

* Explain the role of the skin and mucous membrane in nonspecific defense

-physical factors: barriers to entry, processes that remove microbes from the body's surface -chemical factors: substances made by the body that inhibit microbial growth or destroy them.

*Describe the role of normal microbiota in innate immunity

-prevent overgrowth of pathogens -Microbial Antagonism/ Competitive exclusion (competing for nutrients) -produce substances that are harmful to pathogens -alter conditions that affect survival of pathogens (pH, Oxygen) -(ex- E. coli- produces Bacteriocins- inhibits growth of Salmonella and Shigella) -opportunistic pathogens include E. coli, Staphylococcus aureus, S. epidermidis, Enterococcus faecalis, Pseudomonas aeruginosa, and oral streptococci.

*Provide 3 examples of microbes that cannot be phagocytosed

-some bacteria have structures that inhibit adherence (such as the M protein, and capsules) -Ex 1: M protein of Streptococcus pyogenes- inhibits attachment of phagocyte to their surface and makes adherence more difficult -Ex 2: Streptococus pneumoniae, and Haemophilus influenza- have large capsules (encapsulated microbes can be phagocytosed only if phagocyte traps microbe against arough surface (blood vessel, blood clot, or connective tissue fiber) from which microbe cant slip away -Ex 3. Staphylococcus- produces leukocidins- may kill phagocytes by causing release of phagocytes own lysomal enzyme into its cytolasm (streptolysin released by streptococcus- similar mechanism) -Biofilms- play a role in evading phagocytes -bacteria are more resistant to phagocytosis b/c the phagocytes can't detach bacteria from the biofilm prior to phagocytosis. -neutrophils response against P. aeruginosa in a biofilm is slower than against free-floating bacteria. -although some bacteria in a biofilm (Pseudomonas aeruginosa) can activate the oxidative burst response, it is weaker than in free-floating bacteria. -other microbes: can survive inside phagocytes -Coxiella burnetii- causative agent of Q fever, actually requires the low pH inside a phagolysosome to replicate. -L. monocytogenes, Shigella, and Rickettsia- have ability to escape from a phagosome before it fuses with a lysosome

Basophils

-stain Blue-Purple w/ BASIC dye (methylene blue) -releases HISTAMINES -important to INFLAMMATION and ALLERGIC RESPONSES

The Mechanism of Phagocytosis

1. Chemotaxis-chemical attraction of phagocytes to microbes 2. Adherence (PAMP attaches to TLR) 3. Ingestion- of microbe by phagocyte, pseudopods engulf microbe, formation of phagosome, 4. Digestion-fusion of phagosome w/ a lysosome to form a phagolysosome, microbe is ingested by enzymes in the phagolysosome, formation of residual body containing indigestible material, then discharge of waste materials

*Label the processes that result in phagocytosis: -Margination -Diapedesis -Adherence -Phagolysosome formation

1. Margination-The adhesion of WBCs to the endothelial cells of blood vessels that occurs at the site of an injury during the early phases of inflammation. 2. Diapedesis-the passage of blood cells through the intact walls of the capillaries, typically accompanying inflammation.

The two defensive cells involved in innate immunity are called ...

MACROPHAGES and DENDRITIC CELLS -When the TLRs on these cells encounter the PAMPs of microbes, (such as the LPS of gram neg bacteria), the TLRs induce the defensive cells to release chemicals called cytokines

Physical Factors of the Skin

Physical Factors of Skin: -dermis (inner, thicker) & epidermis (outer, thinner, direct contact w/ env) -top layer of epidermal cells is dead- contains protective protein called keratin -Skin sheds- removes microbes -When skin is moist- skin infections are common (esp fungal infections) -fungi hydrolyze keratin when water is available -microbes RARELY penetrate healthy epidermis -when its BROKEN- subcutaneous infection develops below skin -Staphylococci- normally inhabit epidermis, hair follicles, and sweat and oil glands of skin are likely to cause infection -infections from burns, cuts, stab wounds, etc

*Why do lymph nodes swell during an infection?

Proliferation of lymphocytes are one factor responsible for swelling of lymph nodes during infection -Lymph nodes- site of activation of T and B cells (destroy microbes by immune response) -trap microbes, and macrophages and dendritic cells which destroy microbes by phagocytosis

TLRs and PAMPS

Toll-like receptors (TLR)s-attach to various components commonly found on pathogens that are called pathogen-associated molecular patterns (PAMPs) -ex. LPS outer membrane of Gram neg bacteria, the Flagellin in the flagella of motile bacteria, the peptidoglycan in cell wall of Gram-pos bacteria, DNA of bacteria, and the DNA and RNA of viruses. -TLRs- also attach to components of fungi and parasites. -

*Identify at least one physical and one chemical factor that prevents microbes from entering the body through each of the following a. urinary tract b. reproductive tract

a. Urinary- Physical: Movement out Chemical: Lysozome; acids b. Reproductive tract- Physical: Movement out Chemical: Acidic environment in females

Physical Factors

• 1. The structure of intact skin and the waterproof protein keratin provide resistance to microbial invasion. • 2. Some pathogens can penetrate mucous membranes. • 3. The lacrimal apparatus protects the eyes from irritating substances and microorganisms. • 4. Saliva washes microorganisms from teeth and gums. • 5. Mucus traps many microorganisms that enter the respiratory and gastrointestinal tracts; in the lower respiratory tract, the ciliary escalator moves mucus up and out. • 6. The flow of urine moves microorganisms out of the urinary tract, and vaginal secretions move microorganisms out of the vagina.

Microbial Evasion of Phagocytosis

• 11. Some microbes are not killed by phagocytes and can even reproduce in phagocytes. • 12. Evasion mechanisms include M protein, capsules, leukocidins, membrane attack complexes, and prevention of phagolysosome formation.

Actions of Phagocytic Cells

• 3. Among the granulocytes, neutrophils are the most important phagocytes. • 4. Enlarged monocytes become wandering macrophages and fixed macrophages. • 5. Fixed macrophages are located in selected tissues and are part of the mononuclear phagocytic system. • 6. Granulocytes predominate during the early stages of infection, whereas monocytes predominate as the infection subsides.

The Mechanism of Phagocytosis

• 7. Chemotaxis is the process by which phagocytes are attracted to microorganisms. • 8. Toll-like receptors on a phagocyte adhere to the microbial cells; adherence may be facilitated by opsonization—coating the microbe with serum proteins. • 9. Pseudopods of phagocytes engulf the microorganism and enclose it in a phagosome to complete ingestion. • 10. Many phagocytized microorganisms are killed by lysosomal enzymes and oxidizing agents.