Non-Specific Host Resistance (Microbiology Lecture Notes)

Vocabulary flashcards covering key concepts from the lecture on non-specific host resistance, including barriers, innate defenses, phagocytosis, inflammation, antimicrobial substances, and interferons.

Resistance

The ability to ward off diseases through host defenses (also called immunity).

Susceptibility

Lack of resistance or vulnerability to infection.

Non-specific resistance

Defenses that protect against pathogens regardless of species (innate immunity).

First Line of Defense

Non-specific natural barriers that restrict entry of pathogens (e.g., skin, mucous membranes, secretions).

Second Line of Defense

Innate, non-specific immune defenses that provide a rapid local response after entry (e.g., fever, phagocytes, inflammation, interferons).

Third Line of Defense

Antigen-specific immune responses (adaptive immunity) including antibodies and lymphocytes.

Skin barrier

Intact skin acts as a mechanical barrier preventing pathogen entry.

Epidermis

Outer skin layer; contains Langerhans cells; keratin makes skin waterproof and less hospitable to microbes.

Dermis

Thicker inner skin layer with connective tissue; infections are rarer in intact skin.

Mucous membranes

Secretions trap microbes and limit adhesion; part of first line of defense.

Ciliary escalator

Cilia move debris out of the respiratory tract; helps expel microorganisms via sneezing or coughing.

Epiglottis

Flap that covers the glottis during swallowing to protect the airway from material entering the lower airway.

Urine

Mechanical clearance of organisms by voiding; urinary tract flushed of microbes.

Sebum

Secreted by sebaceous glands; fatty acids inhibit bacterial growth on the skin.

Perspiration

Sweat; contains lysozyme, contributing to antibacterial activity.

Lysozyme

Enzyme that breaks down bacterial cell walls (peptidoglycan); found in tears, saliva, mucus, and sweat.

Gastric juice

Stomach acid (HCl, pH ~1–2) that kills many ingested microbes.

Transferrin

Iron-binding protein that reduces free iron and limits bacterial growth.

Microbial antagonists (Normal flora)

Normal microbiota that prevent pathogen colonization; can become pathogenic if balance is disrupted.

Candida albicans

Opportunistic fungus; part of vaginal/GI flora that can cause candidiasis when balance is disrupted.

Bacteriocin

Toxin produced by normal flora that inhibits growth of other bacteria (e.g., some E. coli).

Leukocytes (white blood cells)

Formed elements of blood involved in defense; increase (leukocytosis) or decrease (leukopenia) during infections.

Platelets

Blood cells that form clots to seal wounds (hemostasis).

Neutrophils

Polymorphonuclear leukocytes; highly phagocytic; first to arrive at infection; major acute responders.

Basophils

Leukocytes that release histamine; involved in inflammation and allergic responses.

Eosinophils

Leukocytes that respond to parasites and are involved in certain hypersensitivity reactions; moderately phagocytic.

Monocytes

Mononuclear phagocytes; become macrophages when in tissues; phagocytic.

Macrophages

Fixed (e.g., Kupffer cells in liver) or wandering phagocytes that digest microbes; key in later inflammation stages.

Phagocytosis

Non-specific engulfing and digestion of microbes by phagocytes; steps include adhesion, ingestion, digestion, and phagolysosome formation.

Adherence (phagocytosis step)

Attachment of the phagocyte to the microbe, often enhanced by opsonization.

Opsonization

Coating of microbes with antibodies (IgG) or C3b to enhance phagocytosis.

Ingestion

Phagosome formation as the microbe is taken into the phagocyte.

Digestion

Destruction of ingested microbes inside a phagolysosome by enzymes and reactive species.

Phagolysosome

Vesicle formed when a phagosome fuses with a lysosome for microbe digestion.

Chemotaxis

Migration of phagocytes toward a site of infection in response to chemical signals (e.g., C5a, IL-8, f-Met).

Margination

Leukocytes adhere to the inner surface of blood vessels before diapedesis.

Emigration/Diapedesis

Movement of leukocytes through vessel walls into surrounding tissue.

Inflammation

Defensive tissue response to injury or infection; aims to contain and destroy pathogens and begin tissue repair.

Cardinal signs of inflammation

Pain (dolor), Heat (calor), Redness (rubor), Swelling (tumor), Loss of function.

Vasodilation

Widening of blood vessels increasing blood flow and permeability during inflammation.

Histamine

Mediator causing vasodilation and increased vascular permeability during inflammation.

Kinins, Prostaglandins, Leukotrienes

Inflammatory mediators that modulate vasodilation and permeability and recruit immune cells.

Complement system

Group of serum proteins activated via classical or alternative pathways; leads to cytolysis (MAC), inflammation, and opsonization.

Classical pathway

Complement activation triggered by antibodies bound to antigen.

Alternative pathway

Complement activation triggered directly by microbial surfaces, without antibodies.

C3

Central component of complement activation; its cleavage drives downstream events.

Membrane Attack Complex (MAC)

C5b-9 complex that forms pores in microbial membranes causing lysis.

Cytolysis

Lysis of pathogens due to MAC formation and membrane disruption.

Opsonization (complement context)

C3b coating that enhances phagocytosis by phagocytes.

Interferons

Antiviral proteins that interfere with viral replication and protect neighboring cells.

Interferon alpha and beta

Produced by virus-infected cells; induce antiviral proteins in neighboring cells.

Interferon gamma

Produced by lymphocytes; activates macrophages and increases MHC expression.

AVPs (antiviral proteins)

Proteins induced by interferons that inhibit viral replication in neighboring cells.

Fever (pyrexia)

Abnormally high body temperature; mediated by hypothalamus and IL-1; can inhibit pathogens and aid repair but may cause dehydration or electrolyte imbalance.

Interleukin-1 (IL-1)

Cytokine associated with fever and the inflammatory response.

Hypothalamus

Brain region that regulates body temperature; modulated during fever.

Tissue repair (stroma vs parenchyma)

Repair processes: stroma (supporting tissue) and parenchyma (functional tissue) regenerate after injury.

Secretory structures and secretions (overview)

Secretions and structures that contribute to barrier defenses (e.g., lacrimal glands, salivary glands, mucus, ciliary action, epiglottis, peristalsis, urination, acidic vaginal secretions).

Lacrimal gland

Tear production; washes and dilutes microbes on the eye surface.

Salivary glands

Saliva washes microbes from teeth and mucous membranes and contains IgA and lysozyme.

Nose hairs and mucus

Filter and trap inhaled particles and microbes.

Mucus

Thick secretion that traps microbes; cleared by ciliary action.

Genito-urinary secretions

Vaginal secretions are acidic and help maintain protection; urination flushes the urethra.

Gastric acidity

Low pH of gastric juice (HCl) that kills many ingested pathogens.