In-Depth Notes on Immunology and the Immune System

University and Course Information

• Institution: Al Salam University, Faculty of Pharmacy
• Location: Gharbia Governorate, Egypt
• Course: General Microbiology and Immunology (PM 401)
• Instructor: Dr. Randa Hesham Khattab

Introduction to Immunology

Definition

• Immunology: Branch of science studying the immune system in both health and diseases, including immunological disorders.
• Immune System Components: Comprised of organs, cells, tissues, and molecules that protect against pathogens like bacteria, viruses, fungi, cancer cells, and non-self proteins (as in organ transplants).

Functions of the Immune System

1. Prevents or limits infections.
2. Recognizes and destroys pathogens (bacteria, viruses, fungi, parasites).
3. Responds to foreign chemicals and compounds.
4. Detects and removes abnormal or damaged cells.
5. Recognizes and responds to foreign organs (tissue graft).
6. Regulates immune response.
7. Remembers past infections for a faster response.

Types of Immunity

1. Innate (Natural) Immunity:

• First line: Physical & chemical barriers (e.g., intact skin, mucous membranes).
• Second line: Internal responses (e.g., phagocytes, natural killer cells).
• Response: Non-specific.

2. Adaptive (Acquired) Immunity:

• Third line: Provides highly specific protection via B cells and T cells.

Characteristics of Adaptive Immunity:

• Diversity: Can respond to millions of different antigens.
• Long Memory: Responds years after initial exposure.
• Specificity: Actions directed against the specific antigen.

Antigens and Antibodies

• Antigen: Any foreign material that stimulates an immune response. Common examples include bacteria, fungi, viruses, and organic pollutants.
• Antibodies (Immunoglobulins): Specific proteins formed in response to antigens, interacting specifically with the antigen that triggered their production.

Lymphoid Organs

The immune system includes various organs and tissues interconnected by blood and lymphatic vessels, through which lymphocytes circulate.

Primary Lymphoid Organs:

• Functions: Development of immature lymphocytes into immunocompetent cells.
• Organs:
  • Bone Marrow
  • Thymus

Secondary Lymphoid Organs:

• Functions: Site of immune responses, trapping foreign antigens for effective exposure to mature lymphocytes.
• Organs:
  • Spleen
  • Lymph Nodes
  • Mucosa-associated Lymphoid Tissue (MALT)

Immune Cell Types

Granular Leukocytes

1. Neutrophils:

   • Comprise 60-70% of innate immune cells, effective in killing bacteria.
   • Associated Conditions: Neutrophilia (acute infection), Neutropenia (increased infection risk).

2. Eosinophils:

   • Comprise 2-4% of leukocytes, active in parasitic infections and allergic reactions.
   • Associated Condition: Eosinophilia (parasitic infections).

3. Basophils:

   • About 1% of leukocytes, involved in inflammatory and allergic reactions.
   • Release mediators (e.g., histamine) upon antigen interaction.

Non-Granular Leukocytes

1. Lymphocytes:
   • B and T lymphocytes involved in specific immune responses.
2. Monocytes:
   • Differentiate into macrophages or dendritic cells in tissues, important in innate immune response.

Lymphocyte Development

• B Lymphocytes:
  • Origin and maturation occur in bone marrow; produce specific antibodies.
• T Lymphocytes:
  • Originate in bone marrow, mature in the thymus; include Helper T cells, Cytotoxic T cells, and Regulatory T cells.

Antigen Presentation

• Antigen Presenting Cells (APCs): Dendritic cells, macrophages, and B cells that present antigens to T cells and link innate and adaptive immunity.

Cytokines

• Function: Chemical messengers that mediate communication between immune cells.
• Types of Cytokine Signaling:
  • Autocrine: Signal affects the same cell.
  • Paracrine: Signal affects nearby cells.
  • Endocrine: Signal travels through the circulatory system to distant cells.

Major Cytokines and Their Sources