Overview of the immune system, its components, and functions. Introduction to basic immunological concepts such as immunity, antigens, antibodies, and immune response.
Introduction to Immunology – Study Guide
1. What Is Immunology?
- Definition: The branch of biomedical science that studies the immune system—its structure, function, development, and disorders.
- Purpose: Understand how the body defends itself against pathogens, how immunity can be harnessed (vaccines, immunotherapy), and why immune failures occur (autoimmunity, immunodeficiency).
2. Core Concepts
| Concept |
Key Points |
| Self vs. Non‑self |
The immune system distinguishes the body’s own cells (self) from foreign entities (non‑self). Failure of this discrimination leads to autoimmunity. |
| Innate Immunity |
First‑line, rapid, non‑specific defense. Includes physical barriers, phagocytes, complement, cytokines, and pattern‑recognition receptors (PRRs). |
| Adaptive Immunity |
Slower, highly specific, generates memory. Mediated by B cells (antibody‑producing) and T cells (cell‑mediated). |
| Immunological Memory |
After an initial encounter, the immune system mounts a faster, stronger response upon re‑exposure. Basis of vaccination. |
| Tolerance |
Mechanisms that prevent immune attack on self‑antigens (central & peripheral tolerance). |
3. Components of the Immune System
3.1 Physical & Chemical Barriers
- Skin – keratinized epithelium, acidic pH, antimicrobial peptides.
- Mucosal surfaces – mucus, cilia, secretory IgA, lysozyme.
3.2 Cellular Elements
| Cell Type |
Primary Functions |
| Neutrophils |
Rapid phagocytosis, release of ROS and NETs. |
| Macrophages |
Phagocytosis, antigen presentation (MHC‑II), cytokine production. |
| Dendritic Cells |
Professional antigen‑presenting cells; bridge innate and adaptive immunity. |
| Natural Killer (NK) Cells |
Detect and kill virus‑infected or transformed cells without prior sensitization. |
| B Lymphocytes |
Differentiate into plasma cells (antibody secretion) and memory B cells. |
| T Lymphocytes |
- CD4⁺ helper T cells (Th1, Th2, Th17, Tfh, Treg)
- CD8⁺ cytotoxic T lymphocytes (CTLs)
|
3.3 Soluble Factors
- Complement system – cascade of plasma proteins that opsonize, lyse pathogens, and recruit immune cells.
- Cytokines & Chemokines – signaling molecules that modulate cell activation, differentiation, and trafficking.
- Antibodies (Immunoglobulins) – IgM, IgG, IgA, IgE, IgD; each with distinct roles and distribution.
4. Innate Immunity in Detail
- Recognition – PRRs (e.g., Toll‑like receptors) bind pathogen‑associated molecular patterns (PAMPs).
- Effector Mechanisms
- Phagocytosis (neutrophils, macrophages).
- Inflammation – vasodilation, increased permeability, recruitment of leukocytes.
- Complement activation – classical, lectin, and alternative pathways.
- Antimicrobial peptides – defensins, cathelicidins.
- Link to Adaptive Immunity – Dendritic cells process antigens and migrate to