Introduction to Immune System

• The immune system consists of various components that protect the body from pathogens.

Chemical Barriers

• Harmful substances such as toxins, destroyed cells, and killed bacteria are expelled from the body via the bladder.
• Saliva is recognized for its protective components and plays a crucial role in oral health.
  • Components of Saliva:
  • Proteins: Include enzymes and immunological factors.
  • Lysozyme: An enzyme that breaks down bacterial cell walls.
  • Lactoferrin: Binds iron and inhibits bacterial growth.
  • Defensins: Antimicrobial peptides that disrupt microbial membranes.
  • Mucus: Acts as a lubricant and helps trap pathogens.
  • Amylase: Enzyme that digests starch.
  • Lingual Lipase: Enzyme that begins fat digestion.
  • Electrolytes and Other Proteins: Aid in various functions including pathogen defense.
  • Saliva contains white blood cells (e.g., neutrophils) rapidly responding to pathogens without harming beneficial bacteria.
  • The complement system in saliva helps destroy pathogens.

Effects of Mouthwash on Oral Flora

• Excessive use of mouthwash, particularly those containing certain chemical agents (like chlorhexidine or triclosan), can negatively impact oral microbiome.
  • Example: A case where a husband faced halitosis (bad breath) due to overuse of mouthwash, resulting in an imbalance of oral bacteria.
  • Treating the condition involved stopping mouthwash use and taking probiotics to restore beneficial bacteria.

Other Chemical Barriers

• Bile Acids: Regulate immune responses and influence inflammation through specific receptors.
• Gastric Acid: Hydrochloric acid with a pH of 1 to 3.5 in the stomach, it destroys many pathogens but some (e.g., Helicobacter pylori) can survive and cause ulcers.

Cellular Immune Response

• Distinction between innate (immediate protection) and adaptive responses (specific protection).
• Key immune cells include:
  • Mast Cells: Involved in allergic responses and initiate inflammation by releasing histamine.
  • Neutrophils: First responders that secrete toxins and promote vascular remodeling.
  • Macrophages: Phagocytic cells capable of engulfing pathogens and maintaining tissue homeostasis.
  • Eosinophils: Play a role in allergies, can elicit hyper-allergic responses leading to anaphylaxis.
  • Natural Killer (NK) Cells: Cytotoxic lymphocytes that target virally infected cells and tumors, functioning within both innate and adaptive immunity.

Origins of Immune Cells

• All immune cells derive from hematopoietic stem cells in the bone marrow. These stem cells can differentiate into various immune cells, including red and white blood cells.

Innate and Adaptive Immunity

• Innate Immune Response:

  • Rapid and nonspecific defense mechanisms.
  • Involves pattern recognition receptors (PRRs) that identify pathogens.

• Adaptive Immune Response:

  • More specific response involving T cells and B cells.
  • Can be trained to recognize specific pathogens (e.g., through vaccinations).

Characterization of Immune Cells

• Macrophages & Neutrophils: Both are versatile in movement and engulfment.
• Cytotoxicity: Neutrophils kill pathogens while macrophages clean debris and signal other immune components.
• Specific identification techniques for cells (e.g., distinguishing between eosinophils and neutrophils under a microscope).

Phagocytosis Overview

• Phagocytosis involves:
  1. Ingestion of pathogens: Through receptors binding to pathogens.
  2. Formation of phagosome: Engulfed pathogen enclosed in a membrane.
  3. Fusion with lysosome: Enzymatic digestion of the contents.
  4. Excretion of digestion residues.

Inflammatory Response

• Characterized by:
  • Heat, pain, redness, swelling, and potential loss of function.
  • Stages of inflammation include recognition, vascular response, cellular recruitment, and tissue repair.
  • Mechanisms of Repair: Include action of macrophages in clearing debris and maintaining homeostasis of tissue.

Signaling Molecules in Immune Response

• Cytokines: Small proteins that regulate immunity and inflammation.
  • Types include interleukins, interferons, tumor necrosis factors, chemokines, colony-stimulating factors, and transforming growth factors.
• **Types of Signaling:
  • Autocrine: Cell stimulates itself.
  • Paracrine: Cell stimulates nearby cells.
  • Endocrine: Cell signals across long distances through the bloodstream.

Complement System Pathways

• Types:
  • Classical Pathway: Triggered by antibody-antigen complexes.
  • Lectin Pathway: Involves mannose-binding lectins recognizing sugars on microbial cell walls.
  • Alternative Pathway: Hydrolyzes complement proteins directly at pathogen surfaces.
• Complement cascades facilitate bridging innate and adaptive immunity.

Closing Remarks

• On the next session: Focus will shift to the adaptive immune response, which involves specialized T and B cells leading to immunological memory.
• Recommended external resources include supplemental video content for visualization of processes discussed.