BSCI 20021: Basic Microbiology - Innate Immunity Study Notes

BSCI 20021: Basic Microbiology

INNATE IMMUNITY

Introduction

• The discussion pivots to the infectious diseases caused by microbes.
• Microbes must interact with both host cells/tissues and the immune system for disease progression.
• Cellular and molecular mechanisms used by microbes to induce disease are often structured to evade or overcome the host's immune response.
• Symptoms of disease partly result from the immune response to the infection.

Immune System Overview

• Innate Immunity:
  • Always active, functioning even in the absence of infection.
• Adaptive Immunity:
  • Activated specifically in response to distinct infections by pathogens.

Barriers to Infection

• There are multiple levels of protection to prevent microbial entry and growth.
  • Anatomical Barriers:
  • Composed of epithelial tissues across body surfaces.
  • Skin is covered with a dry stratified squamous epithelium known as the cutaneous membrane.
  • Internal epithelia are referred to as mucous membranes due to mucus secretion.
  • Physical Barriers:
  • These barriers trap microbes with mucus and effectively slow their penetration into deeper tissues.
  • Damaged pathways can open entry points for pathogens.

Normal Microbiota

• Non-pathogenic Microbes:
  • Resident organisms that act as a biological barrier.
  • These organisms can slow the growth of pathogenic species through a concept known as microbial antagonism.
  • They occupy ecological niches, consuming available nutrients and resources, thus denying space and sustenance to potential pathogens.

Physiological Barriers

• Beyond physical barriers, various surfaces exhibit unique physiological defenses:
  • Skin Composition:
  • High salt concentrations and low availability of moisture.
  • Lower pH (approximately 3.5), which can damage microbial cellular membranes.
  • Mucous Membranes:
  • Protective adaptations in different body areas:
    • Respiratory Tract:
    • Mucus and cilia work together to trap and expel microbes.
    • Digestive Tract:
    • Highly acidic pH (1-2) in the stomach helps to unfold and destroy proteins in microbial pathogens.
    • Physiological secretions reduce pathogen presence.
    • Urinary Tract:
    • Low pH (5-6) helps wash bacteria from the urinary system.

Cellular Defenses

• Defensive Cells:
  • Blood and tissue cells involved in the immune response.
  • Granulocytes:
  • A category of leukocytes involved in innate immunity.
  • Agranulocytes:
  • Another category of leukocytes, also part of the immune continuum.

Reading Assignment

• Students are tasked with reading sections 11.5 and 11.6. They should focus on:
  • Molecular defenses and complement cascade dynamics.
  • Understanding inflammation and the mediating molecules involved.
  • The sequential steps during the inflammation process.
  • Analyzing the relationship between inflammation, pain, and fever.