Immunology-1: Bio-207 Lecture 2

Immunology-1: Bio-207

• Lecture 2 covers the types of the immune system, specifically focusing on white blood cells (WBCs).
• The immune system is comprised of numerous parts that work together, including organs and cells. The main parts include adenoids, mucosa, white blood cells (antibodies, cytokines, complement system, lymph nodes, spleen, tonsils and adenoids, thymus, bone marrow, skin).
• White blood cells (leukocytes) are responsible for defending the body against infections.
• WBCs circulate in the blood and respond to injury or illness.
• WBCs travel through the bloodstream and tissues, locating infection sites to alert other WBCs and fight the invader.
• WBCs produce antibody proteins to attach to the invading organism or toxin and destroy it.
• WBCs account for 1% of blood volume.
• The cells are mostly colorless but can appear light purple/pink when viewed under a microscope after staining.
• They have a round shape and a distinct center membrane (nucleus).
• WBCs are formed in the soft tissue inside bones from cells (stem cells).
• Two types of WBCs (lymphocytes) develop in the thymus (T cells) and lymph nodes/spleen (B cells).

WBC Types

• There are five types of white blood cells:
  • Neutrophils: Defend against bacteria, fungi, and foreign debris.
  • Lymphocytes: Defend against viral infections, produce antibodies to fight infections. They are composed of T cells, natural killer (NK) cells, and B cells.
  • Eosinophils: Fight parasites and cancer cells, and allergic responses.
  • Basophils: Trigger allergic reactions like coughing, sneezing, or runny noses.
  • Monocytes: Defend against infection by cleaning up damaged cells.

WBC Normal Count

• A normal range of white blood cells is between 4,000 and 11,000 cells per microliter of blood.
• The body produces approximately 100 billion white blood cells daily.

Antigens & Antibodies

• Antigens: Substances or toxins in the blood that trigger the body's immune response.
• Antibodies: Proteins that protect the body from invaders by binding to them and initiating their destruction. Antigens are usually bacteria or viruses.
• This battle (fight between antigens and antibodies) is called the immune response.

Heteroantigens & Autoantigens

• Heteroantigens: Foreign substances that initiate the immune response. These can be viruses, bacteria, protozoa, blood/red blood cells from other people, snake venom, certain proteins in foods, and allergens (like pollen).
• Autoantigens: Substances made by the body to fight the body's own cells. Usually a sign of an autoimmune condition.

Lymphocytes

• Lymphocytes are a type of white blood cell crucial for determining the specificity of the immune response.
• B cells and T cells originate in the bone marrow.
• Some lymphocytes travel to the thymus to mature into T cells. Other types remain in bone marrow to develop into B cells.
• Most lymphocytes have short lifespans (a week to a few months), but some can live for years.
• Lymphocytes have "memory." They can respond more quickly to a second encounter with the same antigen.
• Lymphocytes bind to antigens through receptors on their surfaces to help remove them from the body.

Types of Lymphocytes

• Innate lymphocytes: These lymphocytes lack a specific antigen receptor. ILC1, ILC2, ILC3, and NK cells.
• Adaptive lymphocytes: These lymphocytes have a specific receptor for an antigen. T cells, B cells.
• Lymphocytes, when stimulated by a foreign antigen (e.g., bacteria, virus), multiply into identical cells.
  • Some of these differentiate into plasma cells that produce antibodies.
• Antibodies bind to and neutralize or destroy the target antigen.
• There are memory B cells that provide long-term immunity against the target.
• In the thymus: T cells differentiate into helper, regulatory, or cytotoxic cells.
  • Helper T cells release cytokines that stimulate B cells into antibody production.
  • Regulatory T cells control immune reactions, and cytotoxic T cells kill infected cells and cancer cells.