UNIT 4: Overview of the Immune System, Immune Components, and B-cell Activation

Exam Focus: Distinguish between Innate and Adaptive Immunity. The structure of **Immunoglobulins** (Heavy/Light chains, variable/constant regions) and the processes of **Class Switching** and **Affinity Maturation** are central topics in B-cell biology.

Table of Contents

1. Overview of the Immune System
   • Innate and Adaptive Immunity
   • Humoral and Cellular Immune Responses
2. Immune Components
   • B Lymphocytes and T Lymphocytes
   • Structure of Immunoglobulins (Antibodies)
   • T Cell Receptors
3. B-cell Activation: Antibody Production
   • Class Switching (Isotype Switching)
   • Affinity Maturation
   • Heavy Chain Gene Transcription

1. Overview of the Immune System

The immune system is a complex network of cells and organs that protects the body from disease-causing pathogens and abnormal cells.

Innate and Adaptive Immunity

Feature	Innate (Natural) Immunity	Adaptive (Acquired) Immunity
**Specificity**	Non-specific (reacts the same way to all threats).	Highly specific (targets particular antigens).
**Response Time**	Immediate (minutes/hours).	Slow (days/weeks) on first exposure.
**Memory**	No immunological memory.	Has immunological **memory** (faster, stronger response upon re-exposure).
**Components**	Phagocytes, Natural Killer (NK) cells, Complement, Physical barriers.	**B Lymphocytes** and **T Lymphocytes**.