Immunology Chapter 1: Innate vs Adaptive Immunity

Innate and Adaptive Immunity

• Innate immunity is inborn, non-specific, and serves as the first line of defense against pathogens.
• Adaptive immunity is more recent, specific, organized, and involves lymphoid tissues.
• Gene duplication has enhanced the immune system's complexity, resulting in diverse immune molecules.

Innate Immune Mechanisms

• Skin: Produces sebum and sweat containing antimicrobial substances and has microflora to compete with pathogens.
• Gastrointestinal Tract: Small intestinal mucosa has mucus-producing goblet cells and microbial flora that protect against pathogens.
• Respiratory Mucosa: Ciliated epithelial cells move mucus loaded with pathogens out of the airways.
• Urogenital Tract, Mammary Gland, and Ocular Mucosa: Also have protective measures, including antimicrobial substances such as lysozyme and defensins.

Acute and Chronic Inflammation

• Inflammation occurs through both innate and adaptive immunity responding to tissue damage or infection and aims to eliminate pathogens and promote repair.
• Acute Inflammation:
  • Initiates within minutes; characterized by pain, swelling, heat, redness, and loss of function.
  • Involves neutrophil recruitment through chemotaxis and vasodilation for increased blood flow and permeability, causing edema.
  • Alarmins like histamine and cytokines trigger immune responses.
• Chronic Inflammation:
  • Begins 24-48 hours after the initial damage; involves recruitment of monocytes that become macrophages.
  • Macrophages clear dead neutrophils and necrotic tissue, play a role in tissue repair, and release enzymes for tissue remodeling.

Components of the Adaptive Immune System

• T Lymphocytes: Release cytokines and chemokines that regulate immune responses.
• B Lymphocytes: Differentiate into plasma cells that produce antibodies.
• Both types reside in lymphoid tissues, including lymph nodes and spleen.

Role of Dendritic Cells

• Act as a bridge between innate and adaptive immunity by transporting antigens to lymphoid cells.
• Activate antigen-specific T-lymphocytes, which in turn activate B-lymphocytes to mount a stronger immune response at the infection site.

Immune System Regulation

• Essential to regulate the immune response to prevent damage to normal tissues and maintain homeostasis.

Immunological Memory

• After an immune response, the system retains memory for quicker and more effective responses upon re-exposure to the same antigen.
• This principle is foundational for the effectiveness of vaccines.

Evolution of the Immune System

• The innate immune system is considered primitive, possibly originating in unicellular organisms similar to phagocytic cells.
• Historical reliance on innate mechanisms reflects the evolutionary development of immune defense strategies.