Innate and Adaptive Immunity: Physical Barriers, Phagocytosis, Inflammation, Complement, and T Cell Responses

Describe the primary physical and chemical barriers of innate immunity.

Innate immunity is the body's first line of defense that prevents pathogens from entering the body. Physical barriers include the skin and mucous membranes. Chemical barriers include lysozyme in tears/saliva and stomach acid. These barriers block, trap, or destroy microbes before infection spreads, making them essential for protection.

What is the first line of defense in innate immunity?

The first line of defense consists of physical and chemical barriers that prevent pathogens from entering the body.

What are two physical barriers of innate immunity?

The skin and mucous membranes are physical barriers that help block pathogen entry.

What are two chemical barriers of innate immunity?

Lysozyme and stomach acid are chemical barriers that destroy pathogens.

How does lysozyme protect the body?

Lysozyme breaks down bacterial cell walls and helps destroy bacteria.

How does stomach acid help innate immunity?

Stomach acid destroys many pathogens that enter through food or drink.

Why are physical and chemical barriers important?

They prevent infection before pathogens can spread throughout the body.

Outline the steps of phagocytosis and explain their importance.

Phagocytosis is the process by which immune cells engulf and destroy pathogens. The steps are chemotaxis, adherence, ingestion, and digestion. During chemotaxis, phagocytes move toward infection signals, and during ingestion the pathogen is engulfed into a phagosome. Lysosomes digest the pathogen, helping eliminate infection and activate immunity.

What is phagocytosis?

Phagocytosis is the process in which immune cells engulf and destroy pathogens or debris.

What are the steps of phagocytosis?

The steps are chemotaxis, adherence, ingestion, and digestion.

What happens during chemotaxis?

Phagocytes move toward chemicals released from infected or damaged tissue.

What happens during ingestion in phagocytosis?

The phagocyte engulfs the pathogen into a vesicle called a phagosome.

What is the role of lysosomes in phagocytosis?

Lysosomes fuse with the phagosome and digest the pathogen with enzymes.

Why is phagocytosis important?

It destroys pathogens and helps activate immune responses.

Explain the process and purpose of inflammation.

Inflammation is a protective response to tissue injury or infection. Its four main signs are redness, heat, swelling, and pain. Vasodilation and increased vascular permeability allow immune cells and proteins to enter tissues. White blood cells destroy pathogens and remove damaged cells. Inflammation helps contain infection and promote healing.

What is inflammation?

Inflammation is the body's protective response to injury or infection.

What are the four signs of inflammation?

Redness, heat, swelling, and pain.

What causes redness and heat during inflammation?

Vasodilation increases blood flow to the affected area.

What causes swelling during inflammation?

Increased vascular permeability allows fluid to leak into tissues.

Which immune cells are commonly recruited during inflammation?

Neutrophils and macrophages are commonly recruited.

What is the purpose of inflammation?

Inflammation helps contain infection, remove pathogens, and promote tissue repair.

Compare the complement pathways and their functions.

The complement system consists of plasma proteins that enhance immune defenses. The three pathways are classical, lectin, and alternative. The classical pathway is activated by antibodies attached to pathogens. All pathways result in opsonization, inflammation, and membrane attack complex (MAC) formation. Complement is important because it strengthens both innate and adaptive immunity.

What is the complement system?

The complement system is a group of plasma proteins that help destroy pathogens and enhance immunity.

What are the three complement pathways?

Classical, lectin, and alternative pathways.

How is the classical complement pathway activated?

It is activated when antibodies bind to antigens on a pathogen.

What is opsonization?

Opsonization is the coating of pathogens to enhance phagocytosis.

What is the membrane attack complex (MAC)?

The MAC is a protein complex that forms pores in pathogen membranes, causing cell lysis.

Why is the complement system important?

It enhances pathogen destruction and supports immune responses.

Compare humoral and cell-mediated immunity.

Adaptive immunity is a specific immune response against antigens. Humoral immunity involves B cells and antibodies that target extracellular pathogens. Cell-mediated immunity involves T cells that destroy infected cells containing intracellular pathogens. Humoral immunity targets pathogens outside cells, while cell-mediated immunity targets infected cells directly. Both are necessary for complete immune protection.

What is adaptive immunity?

Adaptive immunity is a specific immune response developed after antigen exposure.

What is humoral immunity?

Humoral immunity involves B cells producing antibodies against extracellular pathogens.

What is cell-mediated immunity?

Cell-mediated immunity involves T cells destroying infected or abnormal cells.

What cells are involved in humoral immunity?

B cells and plasma cells.

What cells are involved in cell-mediated immunity?

T lymphocytes, especially cytotoxic T cells.

What is the main difference between humoral and cell-mediated immunity?

Humoral immunity targets extracellular pathogens, while cell-mediated immunity targets intracellular pathogens.

Why are both humoral and cell-mediated immunity important?

Both are needed because pathogens can exist both inside and outside cells.

Explain the role of helper T cells in adaptive immunity.

Helper T cells are CD4+ lymphocytes that coordinate adaptive immune responses. They recognize antigens presented on MHC II molecules. Once activated, they release cytokines that stimulate B cells, cytotoxic T cells, and macrophages. These actions strengthen immune defenses and antibody production. Helper T cells are essential for coordinating adaptive immunity.

What are helper T cells?

Helper T cells are CD4+ lymphocytes that regulate adaptive immune responses.

What type of MHC do helper T cells recognize?

They recognize antigens presented on MHC II molecules.

What do helper T cells release after activation?

They release cytokines.

How do helper T cells activate B cells?

Cytokines released by helper T cells stimulate B cell activation and antibody production.

Why are helper T cells important?

They coordinate and regulate many adaptive immune responses.

Compare MHC I and MHC II.

Antigen presentation is the display of antigen fragments for T cell recognition. MHC I molecules are found on all nucleated cells and present intracellular antigens to CD8+ cytotoxic T cells. MHC II molecules are found on antigen-presenting cells and present extracellular antigens to CD4+ helper T cells. MHC I monitors infections inside cells, while MHC II activates responses against extracellular pathogens. This distinction ensures proper immune activation.

What is antigen presentation?

Antigen presentation is the display of antigen fragments on cell surfaces for T cell recognition.

Where are MHC I molecules found?

MHC I molecules are found on all nucleated cells.

What type of antigen does MHC I present?

MHC I presents intracellular antigens.

Which T cells recognize MHC I?

CD8+ cytotoxic T cells recognize MHC I.

Where are MHC II molecules found?

MHC II molecules are found on antigen-presenting cells.

What type of antigen does MHC II present?

MHC II presents extracellular antigens.

Which T cells recognize MHC II?

CD4+ helper T cells recognize MHC II.

Why is the difference between MHC I and MHC II important?

It ensures the correct immune cells respond to different infections.

Compare bactericidal and bacteriostatic drugs.

Bactericidal drugs kill bacteria directly, while bacteriostatic drugs inhibit bacterial growth. Bactericidal drugs reduce the number of living bacteria, whereas bacteriostatic drugs rely on the immune system to remove inhibited microbes. Penicillin is bactericidal because it destroys cell walls, while tetracycline is bacteriostatic because it blocks protein synthesis. The distinction is clinically important when selecting treatments.

What are bactericidal drugs?

Bactericidal drugs kill bacteria directly.

What are bacteriostatic drugs?

Bacteriostatic drugs inhibit bacterial growth and reproduction.

How do bacteriostatic drugs depend on the immune system?

The immune system must eliminate bacteria after their growth is inhibited.

Give an example of a bactericidal drug.

Penicillin is a bactericidal drug.

Give an example of a bacteriostatic drug.

Tetracycline is a bacteriostatic drug.

Why is the difference between bactericidal and bacteriostatic important?

It affects treatment choices depending on infection severity and immune status.

Explain how sulfonamides inhibit microbial growth.

Sulfonamides are antimicrobial drugs that block bacterial folic acid synthesis. They mimic PABA, which bacteria need to produce folic acid. Without folic acid, bacteria cannot synthesize DNA or essential molecules. This prevents bacterial growth and reproduction. Selective toxicity occurs because humans obtain folic acid from food rather than synthesizing it.

What are sulfonamides?

Sulfonamides are antimicrobial drugs that inhibit bacterial folic acid synthesis.

What molecule do sulfonamides mimic?

Sulfonamides mimic PABA.

How do sulfonamides affect bacteria?

They block folic acid synthesis, preventing DNA production and growth.

Why do sulfonamides show selective toxicity?

Humans obtain folic acid from diet, while bacteria must synthesize it.

Describe mechanisms of antimicrobial resistance.

Antimicrobial resistance is the ability of microbes to survive exposure to drugs that once killed them. Resistance mechanisms include drug-destroying enzymes, efflux pumps, and altered target sites. Some bacteria produce beta-lactamase enzymes that destroy penicillin antibiotics. Resistance often develops from misuse or overuse of antimicrobial drugs. Antimicrobial resistance is dangerous because it makes infections harder to treat.

What is antimicrobial resistance?

Antimicrobial resistance is the ability of microorganisms to survive antimicrobial drugs.

What are common mechanisms of antimicrobial resistance?

Drug-destroying enzymes, efflux pumps, and altered target sites.

What do efflux pumps do?

Efflux pumps remove antimicrobial drugs from microbial cells.

What are altered target sites?

Altered target sites prevent antimicrobial drugs from binding effectively.

What is beta-lactamase?

Beta-lactamase is an enzyme that destroys beta-lactam antibiotics like penicillin.

What commonly causes antimicrobial resistance?

Misuse and overuse of antimicrobial drugs.

Why is antimicrobial resistance a major concern?

It makes infections more difficult to treat and increases disease risk.