Microbiology Exam 4

Unit 17 & 18

Compare innate/natural defenses and adaptive immunities

Innate Defenses: Present at birth, provide nonspecific resistance to infection, and act immediately. Adaptive Immunities: Specific, must be acquired through exposure, and have memory.

Contrast innate/natural defenses and adpative immunities

Innate is nonspecific and immediate, adaptive is specific and it takes time to develop

Of the 3 lines of defense discussed, which are innate and which are adaptive?

Innate is the first line (barriers) and second line (nonspecific chemical/cellular) and adaptive are the third line of defense (acquired immunity)

Explain the main function of the first line of defense

blocks invasion at the portal of entry (barriers)

Explain the main function of the second line of defense

internalized system of protective cells and fluids (inflammation, phagocytosis) acting when the first line is breached

Explain the main function of the third line of defense

provides long-term, specific immunity via lymphocytes and antibodies

What are the 4 categories of nonspecific defenses in the first line of defense?

1. Physical/anatomical barriers

2. Chemical defenses

3. Genetic resistance

4. Microbiota (microbiome)

Give several examples of physical defenses

Skin (tough, waterproof keratin, shedding), Mucous membranes (mucus traps microbes), Cilia (move trapped microbes), Urine/Tears (flushing action)

Give several examples of chemical defenses

Sebaceous secretions, Lysozyme (in tears/saliva), High lactic acid in sweat, Skin's acidic pH, Hydrochloric acid in the stomach, Digestive juices, Semen (antimicrobial chemicals), Acidic pH of the female genitals

Describe the role of antimicrobial peptides and give examples

These are short proteins that insert themselves into bacterial membranes, disrupting them (e.g., Defensins).

How does genetic variation play a role in immune response?

Some hosts are genetically immune to the diseases of other hosts (e.g., humans are immune to certain animal viruses) or individuals may carry genes that make them resistant to specific pathogens (e.g., sickle cell trait and malaria resistance).

Describe the role of microbiota as a first-line defense

Microbial Antagonism: Commensal microbes block the access of pathogens to epithelial surfaces and create an unfavorable environment (competing for nutrients, altering pH).

What is the primary goal of the immune system?

To survey the body, recognize foreign material (non-self), and destroy it

List all of the white blood cell (WBC) types and briefly describe their role.

• Neutrophils: Phagocytes; active engulfers and killers of bacteria.

• Eosinophils: Active in worm and fungal infections, allergy, and inflammation.

• Basophils: Function in inflammatory events and allergies (release histamine).

• Monocytes: Blood phagocytes that rapidly leave the circulation; mature into Macrophages (largest phagocytes) and Dendritic cells (relatives of macrophages, process antigens).

• Lymphocytes: Primary cells of the adaptive immune response (B cells produce antibodies; T cells perform cell-mediated immunity).

Platelets serve what role during an injury

They are involved in blood clotting (hemostasis) and releasing chemicals that act in inflammation.

Explain how lymph is formed, what lymph transports and the overall role of the lymphatic system

• Formation: Formed when blood components move out of blood vessels into extracellular spaces.

• Transports: White blood cells (especially lymphocytes), fats, cellular debris, and infectious agents.

• Role: Acts as a drain-off system for the inflammatory response, renders surveillance, and recognition against foreign material.

Where do WBCs examine and filter lymph for possible foreign materials

lymph nodes

Differentiate between the primary and secondary lymphoid organs.

Primary: Sites of lymphocytic origin and maturation (e.g., Thymus for T cells, Bone Marrow for B cells).

Secondary: Sites where lymphocytes bind antigen and become activated (e.g., Lymph nodes, Spleen, MALT, GALT).

Define and differentiate between cytokines and chemokines. What is a cytokine storm?

Cytokines: Chemical messengers secreted by cells to regulate immunity and inflammation.

Chemokines: A subset of cytokines that specifically trigger chemotaxis (migration of cells to a chemical stimulus).

Cytokine Storm: An overproduction of cytokines that causes severe damage to the body (e.g., stimulated by Superantigens)

What is the primary purpose of interferons?

They are small proteins produced by virus-infected cells that warn nearby uninfected cells to produce antiviral proteins, inhibiting viral replication.

What induces monocytes to become a macrophage or dendritic cell

Migrating out of the bloodstream into the tissues induces monocytes to differentiate into macrophages or dendritic cells.

Process of WBC exiting a blood vessel and properties required.

Diapedesis: The migration of WBCs out of blood vessels into tissues.

Chemotaxis: The tendency of WBCs to migrate in response to a specific chemical stimulus.

What are the 4 symptoms of inflammation?

Rubor (Redness), Calor (Warmth), Tumor (Swelling), Dolor (Pain).

Describe the major inflammatory events.

1. Injury/Immediate Reactions: Vasoconstriction, release of chemical mediators.

2. Vascular Reactions: Vasodilation (increased blood flow), increased permeability (leakage).

3. Edema and Pus Formation: Accumulation of fluid (exudate) and neutrophils (pus).

4. Resolution/Scar Formation: Macrophages clear debris, tissue repair

How is a fever initiated and what are the benefits?

Initiated: By pyrogens (exogenous or endogenous) which reset the hypothalamus to a higher temperature.

Benefits: Inhibits multiplication of temperature-sensitive microorganisms, impedes bacterial nutrition (reduces iron availability), and increases metabolism/stimulates immune reactions.

What are the 3 types of complement pathways?

Classical, Lectin, and Alternative pathways.

What is the end result of the complement cascade?

The formation of the Membrane Attack Complex (MAC), which punches holes in the pathogen's membrane, causing lysis.

List the steps of phagocytosis

• Chemotaxis (movement toward pathogen).

• Adhesion (binding to pathogen).

• Engulfment (ingestion into a vacuole).

• Phagosome formation.

• Phagolysosome formation (fusion with lysosome).

• Destruction/Killing (via enzymes and reactive oxygen species).

• Excretion (release of debris)

How do phagocytes kill pathogens?

They use antimicrobial enzymes (e.g., lysozyme) and reactive oxygen species (e.g., hydrogen peroxide, superoxide) within the phagolysosome.

What is immunocompetence?

The ability of the body to interact with a wide spectrum of foreign substances.

Differentiate between Humoral and Cell-mediated immunity

Humoral Immunity: B-cells produce antibodies that combat foreign molecules; functions as a "free floating" defense in fluids.

Cell-mediated Immunity: T-lymphocytes recognize antigens and act directly on other cells (Cell to Cell function)

What are the main goals of adaptive immunity?

Specificity: Antibodies/cells function only against the antigen they were produced in response to.

Memory: Lymphocytes are programmed to "recall" their first encounter and respond rapidly to subsequent encounters.

What is the Major Histocompatibility Complex (MHC)?

A set of cell surface proteins (receptors) essential for the recognition of self and rejection of foreign molecules

Differentiate between Class I and Class II MHC

Class I MHC: Found on all nucleated cells. Display unique characteristics of "self" and allow recognition of self-molecules.

Class II MHC: Found on Antigen Presenting Cells (APCs: macrophages, dendritic cells, B cells). Involved in presenting antigen to T-cells

Why is it beneficial that red blood cells do not have MHC molecules?

RBCs are the only cells without MHC. This allows them to be transfused into other individuals (of matching blood type) without being immediately rejected by the recipient's T-cells looking for foreign MHC markers.

Differentiate between antigens and immunogens

Antigen (Ag): A substance that elicits an immune response.

Immunogen: A type of antigen that actually induces a specific immune response (some antigens are too small or poor quality to be immunogens unless attached to a carrier).

What characteristics make a molecule antigenic

Foreignness, size (large molecules >10,000 MW are better), shape, and accessibility.

What are epitopes?

Small molecular groups on an antigen (antigenic determinants) that are recognized by lymphocytes

Differentiate between Alloantigens, Superantigens, Allergens, and Autoantigens.

Alloantigens: Cell surface markers that occur in some members of the same species but not others (e.g., blood types).

Superantigens: Potent T-cell stimulators that can cause a "cytokine storm" (e.g., Toxic Shock Toxin).

Allergens: Antigens that evoke allergic reactions.

Autoantigens: Molecules on self-tissues for which tolerance is inadequate (autoimmunity).

Descriibe the development of T and B lymphocytes

• Stem cells in the bone marrow differentiate into T or B cells.

• B cells stay in the Bone Marrow to mature.

• T cells migrate to the Thymus to mature.

• Both migrate to secondary lymphoid tissues.

Describe the receptors for B-cell and T-cell receptors

B-cell receptors: Bind free antigens.

T-cell receptors (TCR): Bind processed antigens together with MHC molecules on APCs.

What is the Clonal Selection Theory

Lymphocyte specificity is genetically preprogrammed. The introduction of an antigen "selects" a specific genetically distinct lymphocyte (clone) and causes it to expand (multiply) into a population of cells that react to that antigen.

Differentiate between Helper T-cells and Cytotoxic T-cells.

Helper T-cells (CD4): Activated by MHC II on APCs; activate other CD4/CD8 cells, drive B-cell proliferation, and stimulate macrophages.

Cytotoxic T-cells (CD8): Activated by MHC I; destroy infected cells (using perforins and granzymes) and cancer cells.

What are Antigen Presenting Cells (APCs)? List the 3 types

Phagocytes that process T-cell dependent antigens and present them to T cells.

Types: Macrophages, Dendritic cells (most common), and B cells.

Describe B-cell activation and differentiation.

A B-cell binds an antigen and processes it. It interacts with a Helper T-cell (which secretes cytokines/interleukins). The B-cell then differentiates into Plasma Cells (which secrete antibodies) and Memory B Cells (for future protection).

Describe the structure and function of Antibodies (Immunoglobulins).

• Y-shaped proteins with antigen-binding sites (Fab) and a biological activity region (Fc).

• Functions:

  • Opsonization: Coating microbes to enhance phagocytosis.

  • Neutralization: Blocking viral attachment or toxin activity.

  • Agglutination: Clumping cells together.

  • Complement Fixation: Activating the complement pathway (lysis).

  • Precipitation: Clumping soluble antigens.

List the 5 characteristics of immunoglobulins and their characteristics

• IgG: Most abundant, crosses placenta, long-term immunity.

• IgA: Found in secretions (mucus, tears, breastmilk).

• IgM: Pentamer (5 units), first produced during primary response.

• IgD: Receptor on B cells.

• IgE: Associated with allergies and worm infections.

Differentiate between primary and secondary immune responses

Primary: Slower, latent period, produces IgM followed by IgG.

Secondary (Anamnestic): Rapid, stronger response due to memory cells; predominantly IgG.

Differentiate between the 4 types of acquired immunity

• Natural Active: Immunity from getting an infection.

• Natural Passive: Mother to child (breastmilk, placenta).

• Artificial Active: Vaccination.

• Artificial Passive: Immunotherapy (injection of antibodies)

What is herd immunity?

Immune individuals protect non-immune individuals by reducing the occurrence/spread of the pathogen in the population.

Describe the types of vaccine preparations.

• Whole cell: Killed (inactivated) or Attenuated (live but weakened).

• Subunit: Antigenic parts of the pathogen.

• Toxoid: Inactivated toxins.

• Conjugate: Antigen linked to a carrier protein to boost response.

• Genetically Engineered: DNA vaccines, mRNA vaccines.

How does an mRNA vaccine work?

Human cells pick up a plasmid/mRNA and express microbial DNA/RNA as proteins, causing B and T cells to respond and form memory cells.

What are posssible side effects of vaccines?

Local reaction at injection site, fever, allergies; rarely neurological effects

Differentiate between intrinsic and extrinsic factors.

• Intrinsic: Factors inherent to the food itself (e.g., pH, water activity, nutrient content, biological structure).

• Extrinsic: Environmental factors where the food is stored (e.g., temperature, humidity, presence of gases).

What are the methods of microbial control in food? What are the methods applied using temperature?

• Methods: Heat, cold, drying (desiccation), irradiation, chemical preservatives.

• Temperature methods:

  • Heat: Pasteurization (kills pathogens), Canning (commercial sterilization), Cooking.

  • Cold: Refrigeration (slows growth - bacteriostatic), Freezing (stops growth, may kill some).

How does water availability influence microbial growth?

Microbes need water to grow. Water activity (aw) measures available water. Reducing aw (by drying or adding salt/sugar) inhibits growth. Bacteria usually require higher aw than fungi.

What types of food are most likely to be irradiated? Why?

• Foods: Spices, meats, vegetables, fruits.

• Why: To kill pathogens and insects, and extend shelf life without using heat ("cold pasteurization"), preserving taste and nutrition.

What are the two primary types of food borne disease and how are they transmitted

• Food Infection: Ingestion of live microbes that grow in the intestine and cause disease (e.g., Salmonella).

• Food Intoxication: Ingestion of a pre-formed toxin produced by microbes in the food (e.g., Staphylococcus aureus, Botulism).