Host Defenses Quiz

Host Defenses

• A multilevel network of innate nonspecific protections and specific immunities, categorized as the first, second, and third lines of defense.
• First and second lines are innate, natural defenses present at birth, providing nonspecific resistance to infection.
• Third line is adaptive immunity, specific and acquired.
• Defense systems overlap and are sometimes redundant.

First Line of Defense

• Innate, nonspecific barriers against microorganisms.
• Includes any barrier blocking invasion at the portal of entry, preventing access to the internal environment.

Second Line of Defense

• Innate, nonspecific.
• More internalized system of protective cells and fluids (e.g., inflammation, phagocytosis).
• Acts rapidly at local and systemic levels once the first line is breached.

Third Line of Defense ("Adaptive Immunity")

• Acquired, specific immunity.
• Highly specialized response tailoring the full capabilities of the immune system to individual invading microbes.
• Utilizes specific lymphocytes and antibodies for targeted chemical attack on specific microorganisms.

First Line of Defense - Physical/Anatomical Barriers

• Skin and mucous membranes of respiratory, urogenital, eyes, and digestive tracts.
  • Outermost skin layer (epithelial cells compacted with keratin) is a strong barrier.
  • Flushing effect of sweat glands, blinking, and tear production aid in prevention of pathogen entry.

Nonspecific Chemical Defenses

• Stomach acid: Inhibits bacterial attachment and entry.

• Mucous coat: Impedes bacterial attachment.

• Nasal hair: Traps larger particles.

• Sebaceous secretions: Contain lysozyme to hydrolyze bacterial cell walls.

• Tears, sweat, skin's acidic pH, saliva, and digestive juices: Inhibit microbial growth.

• Vaginal secretions: Have an acidic pH, inhibiting growth

Immunology

• The study of all biological, chemical, and physical events surrounding immune system function.
• The immune system is a complex and diffuse network of cells and fluids throughout the body, including fluids and tissues/organs.

Surveillance

• Continuously scouts the body for foreign material.
• Distinguishes between self (self markers) and foreign markers (antigens).
• Attacks and destroys foreign invaders.

Definitions

• Leukocytes (white blood cells): Innate capacity to recognize foreign material (non-self) from normal cells (self).
• Pathogen recognition receptors (PRRs): Receptors on white blood cells (WBCs) (e.g., toll-like receptors) that sense pathogens via pathogen-associated patterns (PAMPs) on microorganisms.

Immune System Subdivision

• Extracellular fluid (ECF): Fluid outside cells.
• Reticuloendothelial system (RES): Connective tissue fluids and fibers, rich in phagocytic cells (macrophages).
• Blood: Contains plasma (liquid portion) and formed elements (blood cells).
  • Serum: Plasma minus clotting factors.

Reticuloendothelial System (RES)

• Connective tissue fibers interconnecting cells and organs.
• Inhabited by phagocytic cells (mononuclear phagocyte system), ready to attack and ingest microbes

Blood Origin, Composition, and Function

• Whole blood comprises plasma and formed elements.
• Plasma is about 92% water, with various proteins, globulins, clotting factors, hormones, and other components for various bodily functions.
• Formed elements are made in red bone marrow.
• Erythrocytes (RBCs): Most numerous, carry oxygen and carbon dioxide.
• Platelets: Formed elements crucial in blood clotting.
• Leukocytes (WBCs): Includes granulocytes (neutrophils, eosinophils, basophils), and agranulocytes (monocytes, lymphocytes).

Leukocytes-types

• Basophils: Dark blue granules, release potent chemicals influencing immediate allergy/inflammation.

• Mast cells: Non-motile, bound to connective tissue, involved in releasing histamine.

• Lymphocytes: Specific immune response – B cells (antibodies, humoral immunity), T cells (cell-mediated immunity, modulate immune functions).

• Monocytes & Macrophages: Phagocytic; final differentiation of monocytes leads to macrophages.

• Dendritic cells: Trap pathogens, participate in immune reactions.

Lymphatic Fluid and Vessels

• Lymph is plasma-like fluid carried by lymphatic circulation.
• Lymphatic capillaries permeate most body parts except CNS, bone, thymus, and placenta.
• Return lymph to circulation, toward the heart, involving skeletal muscle contractions.

Lymph Organs/Tissues

• Primary organs: Sites for lymphocyte origin/maturation (bone marrow, thymus).
• Secondary organs/tissues: Encounter sites for microbes and immune responses (lymph nodes, spleen, gut-associated lymphoid tissue (GALT)).

Inflammation

• Body’s response to injury; aids in destruction/spread of microbes.
• Classics signs: rubor (redness), calor (heat), tumor (swelling), and dolor (pain).
• Increased blood flow to injured tissues; fluids and cells (WBCs, microbes, debris) collect to form pus, preventing spread of infection.

Fever

• Abnormally elevated body temperature, regulated by the hypothalamus.
• Exogenous pyrogens: Products of microbes.
• Endogenous pyrogens: Substances released by immune cells (e.g., IL-1, TNF) during phagocytosis.
• Fever benefits by inhibiting microbial multiplication, limiting nutrient availability to pathogens, and stimulating immune responses.

Phagocytosis

• General activities of phagocytes: survey tissue compartments for microbes, particulate matter, and dead/injured cells, ingest and eliminate materials
• Includes neutrophils, eosinophils, and monocytes/macrophages.

Cytokines

• Chemical mediators produced by immune cells and damaged tissue, regulating, stimulating, and limiting immune reactions.
• Examples: histamine, IL-1, IL-2, interferon.

Interferon

• Cytokine released by host cells to nonspecifically inhibit viral spread.
• Types: alpha, beta, and gamma, targeting different cell types (lymphocytes, fibroblasts, epithelial cells, T-cells).

Complement System

• Complex system of 26 blood proteins working concertedly to destroy bacteria and some viruses.
• Pathways: Classic and alternate pathways activate in cascade reaction.
• Forms membrane attack complex (MAC) to kill microbes by creating holes in their surfaces.
• Functions: Chemotaxis, opsonization of microbes (coating for enhanced phagocytosis), and inflammation stimulation.

Natural Killer (NK) Cells

• Type of T cell (nonspecific cytotoxic).
• Destroy virus-infected cells and tumor cells.
• Found in different tissues.
• Activated by various stimuli/cytokines.