Immune Response Quiz

First Line of Defense: Skin and Mucous Membranes

• Skin acts as a physical barrier, consisting of tightly packed cells with keratin, a protective protein.
• Mucous membranes trap microbes.
• Ciliary escalator transports trapped microbes away from lungs.
• Secretions like tears, saliva, urine, and vaginal secretions help wash away invaders.
• Normal microbiota plays a role in preventing pathogens from colonizing.
• Chemical factors such as low pH, lysozyme, and fungistatic fatty acids in sebum also contribute to the first line of defense.

Physical Factors

• Skin's epidermis is a tightly packed layer of cells with keratin.
• Mucous membranes trap microbes with mucus.
• Ciliary escalator transports trapped microbes from the lungs.
• Secretions like tears, saliva, urine, and vaginal secretions wash away invaders.

Chemical Factors

• Sebum (sebaceous glands) contains fungistatic fatty acids.
• Skin has a low pH (3-5) due to fatty acids and lactic acid.
• Perspiration, tears, saliva, and urine contain lysozyme.
• Gastric juice has a low pH (1.2-3.0) due to HCl and enzymes.
• Vaginal secretions have a low pH (3-5) due to lactic acid bacteria.

Second Line of Defense

• Phagocytes: neutrophils, eosinophils, dendritic cells, and macrophages.
• Inflammation.
• Fever.
• Antimicrobial substances.

Phagocytosis

• Phagocytosis is the ingestion of microbes or particles by a cell, performed by phagocytes.
• Phagocytes bind to microbes (chemotaxis and adherence).
• Microbes are engulfed (ingestion).
• Microbe is digested in a phagolysosome.
• Waste materials are discharged.

Inflammation

• Inflammation is a reaction to tissue damage.
• Key symptoms include redness, swelling (edema), pain, and heat.
• Cytokines like TNF-a activate acute-phase proteins, amplifying the response.
• Three stages: vasodilation, phagocyte migration/phagocytosis, and tissue repair.
• Chemicals like histamine, kinins, prostaglandins, leukotrienes, and cytokines are released from damaged cells.

Fever

• Fever is a systemic reaction to infection.
• The hypothalamus normally maintains a temperature of 37°C.
• Phagocytes release cytokines (e.g., IL-1, TNF).
• Cytokines trigger prostaglandin release, resetting the hypothalamus to a higher temperature.
• Body increases rate of metabolism, promotes shivering, and constricts blood vessels (chills).
• Increased body temperature decreases when vasodilation and sweating occur.

Antimicrobial Substances

• Complement system is a group of serum proteins that work in a cascade.
• Activated by antibodies or antigens directly.
• Leads to inflammation, cytolysis (cell lysis), and opsonization.
• Interferons are antiviral proteins.
• Iron-binding proteins sequester iron needed for microbial growth.
• Antimicrobial peptides directly kill microbes.

The Lymphatic System

• Transports fluid back to the bloodstream, recycles plasma proteins, delivers leukocytes, and filters out invaders.
• Contains lymph fluid, lymphatic vessels, and lymphatic tissue (nodes and organs like spleen, thymus).
• Lymph capillaries collect interstitial fluid (lymph) and return it to the bloodstream.

Adaptive Immunity

• Adaptive immunity: induced resistance to specific pathogens.
• Differentiates into humoral (antibody-mediated) and cellular (cell-mediated) immunity.
• B cells mature in bone marrow, producing antibodies targeting specific antigens.
• T cells mature in the thymus, performing cell-mediated immune responses via T cell receptors, attacking intracellular pathogens.

Antibodies and Antigens

• Antigens are substances that trigger an immune response (antibodies or sensitized T cells).
• Antibodies (immunoglobulins) interact with epitopes (antigenic determinants) on antigens.
• Haptens are small antigens that need a carrier molecule to trigger an immune response.

B Cells

• B cells are activated by T-helper cells (dependent antigens) or by antigens directly (independent antigens).
• Activated B cells differentiate into plasma cells producing antibodies and memory cells.
• Clonal selection ensures specific antibodies are produced for each antigen.
• Clonal deletion removes B cells that react with self-antigens to prevent autoimmune responses.

T Cells

• T cells respond to antigens presented by antigen-presenting cells (APCs).
• T helper (TH) cells activate other immune cells (e.g., macrophages, cytotoxic T cells).
• Cytotoxic T (TC) cells directly kill infected cells.
• Regulatory T (Treg) cells suppress immune responses.
• Activated macrophages have enhanced phagocytosis, and Natural Killer (NK) cells destroy cells that lack MHC I.

Antibody-Dependent Cell-Mediated Cytotoxicity (ADCC)

• Antibodies tag target cells for destruction by other immune cells (e.g., macrophages or eosinophils).
• Important for eliminating large parasites that cannot be engulfed.

Immunological Memory

• The primary response occurs after initial exposure to an antigen; the secondary response is faster.
• Memory cells are formed during the primary response, allowing a faster and stronger secondary response if the same antigen is encountered again.

Types of Adaptive Immunity

• Naturally acquired active immunity occurs after an infection.
• Naturally acquired passive immunity occurs when antibodies are transferred from mother to offspring.
• Artificially acquired active immunity occurs after vaccination.
• Artificially acquired passive immunity occurs after injection of antibodies.

Antibiotic Resistance

• Antibiotic misuse leads to resistance mutants.
• Outdated antibiotics, inappropriate use (common colds),using antibiotics in animal feed, and incomplete prescription regimens contribute to the problem.
• The overuse of triclosan contributes to multidrug-resistant bacteria.
• Resistance genes often reside on plasmids or transposons and can move between bacteria.

Antimicrobial Drugs

• Bactericidal drugs directly kill microbes.
• Bacteriostatic drugs prevent microbial growth.
• Synergistic interactions amplify drug efficacy.
• Antagonistic interactions weaken drug efficacy.
• Mechanisms of action may target cell walls, protein synthesis, nucleic acid synthesis, or cell membranes. Polyenes, azoles, and allylamines inhibit ergosterol synthesis while glycoproteins and echinocandins inhibit synthesis of-glucan. Quinolones and fluoroquinolones inhibit DNA gyrase; sulphonamides inhibit folic acid synthesis. Inhibitors of cell wall synthesis like penicillin, cephalosporins, and vancomycin targets cell wall synthesis.

Antiviral Drugs

• Entry inhibitors prevent viruses from entering cells; fusion inhibitors prevent viral envelope fusion.
• Nucleoside analogs block viral DNA synthesis .
• Interferons prevent viral spread to new cells.