Immunology-1 Lecture 2: Immune System Types

Immunology-1 Lecture 2: Types of Immune System

• The immune system is composed of many organs and cells that work together to maintain health.
• White blood cells (WBCs) are crucial components of the immune system.
• WBCs, also known as leukocytes, protect the body from infection.
• WBCs circulate in the bloodstream and tissues, identifying and responding to infection sites.

White Blood Cells (WBCs) - Characteristics

• WBCs are colorless, but can appear light purple or pink when stained and viewed under a microscope.
• They have a round shape with a distinct central membrane, or nucleus.
• WBCs represent approximately 1% of total blood volume; red blood cells are more prevalent.

WBC Formation

• WBCs originate from cells that develop into other cells, specifically stem cells, found within the bone marrow.
• White blood cell development also occurs in the soft tissue inside bones (bone marrow).
• Different types of white blood cells, such as lymphocytes (including B cells and T cells), develop in different locations (thymus, lymph nodes, and spleen).

WBC Types

• Five types of white blood cells:
  • Neutrophils: Protect the body by killing bacteria, fungi, and foreign debris.
  • Lymphocytes: Include T cells, natural killer cells, and B cells; protect against viral infections and produce antibodies.
  • Eosinophils: Destroy parasites, cancer cells, and play a role in allergic responses.
  • Basophils: Trigger allergic reactions, such as coughing, sneezing, or a runny nose.
  • Monocytes: Defend against infection by cleaning up damaged cells.

WBC Normal Count

• A normal count of white blood cells ranges between 4,000 and 11,000 cells per microliter of blood.
• Approximately 100 billion WBCs are produced daily.

Antigens & Antibodies

• Antigens: Substances or toxins in the blood that trigger the immune system's response.
  • Antigens are primarily bacteria or viruses, but can also include other foreign substances.
  • The immune system's response to antigens is called an immune response.
• Antibodies: Proteins that protect the body from invaders by binding to and destroying them.

Heteroantigens and Autoantigens

• Heteroantigens: Foreign substances to the body, including viruses, bacteria, protozoa, blood/red blood cells from others, snake venom, and allergens (like pollen) or food proteins.
• Autoantigens: Proteins made by the body to fight the body's own cells; often a sign of autoimmune diseases.

Lymphocytes

• Lymphocytes (a type of WBC) are crucial for determining the specificity of the immune response to infections and foreign substances.
  • B cells and T cells originate in bone marrow and in some cases mature in the thymus.
  • Most lymphocytes have a short lifespan — a few weeks to a few months.
  • However, some lymphocytes have longer lifespans to maintain long-term immune responses and memory.
• Lymphocytes are able to respond rapidly to subsequent encounters with the same antigen.
• Lymphocytes recognize foreign antigens (non-self) to help remove them from the body.
• Each lymphocyte has receptors that bind to a specific antigen.

Lymphocyte Activation

• Lymphocytes multiply and differentiate upon stimulation by a foreign antigen, including bacteria or viruses.
• Activated lymphocytes differentiate into other cell types with specific functions.
  • B cells differentiate into plasma cells to produce antibodies that bind to the antigen.
  • Helper T cells secrete cytokines that activate other white cells to help destroy and eliminate the antigen.
  • Some lymphocytes become memory cells to create a rapid response if the same antigen is encountered again.
• Cytotoxic T cells destroy infected cells.
• Regulatory T cells control immune reactions.

Types of Lymphocytes

• Innate lymphocytes (ILCs) and adaptive lymphocytes (B cells and T cells) are two main classes.
  • ILCs are innate lymphocytes that do not have T-cell receptors.
  • Adaptive lymphocytes use T-cell or B-cell receptors.

Dive into the second lecture of Immunology-1, focusing on the various types of the immune system and the essential role of white blood cells (WBCs). Learn about their characteristics, formation, and how they protect the body from infections. Enhance your understanding of immunology through this informative session.