AP Bio: The Immune System - Part 1

Introduction to the Immune System

• Discussion on the immune system's function and personal context of being sick during the lecture.

Types of Blood Cells

• Red Blood Cells (RBCs):

  • Shaped like a doughnut with an incomplete hole.

• White Blood Cells (WBCs):

  • Often phagocytic, appearing whitish.

  • Integral to the immune system.

Lines of Defense in the Immune System

• First Line of Defense:

  • Physical Barrier: Skin acts as a barrier to protect interstitial fluid and blood.

  • Secretions: Antimicrobial proteins and mucus help capture and eliminate pathogens.

• Second Line of Defense:

  • Non-Specific Defense Mechanisms:

    • Antimicrobial proteins in the blood go after general pathogens.

    • WBCs attack non-self cells, acting like 'bouncers' rather than specific hunters.

Types of White Blood Cells

• Neutrophils:

  • Comprise ~70% of WBCs.

  • Function as infantry, responding to infection.

  • Pus is a result of neutrophil activity.

• Macrophages:

  • Matured monocytes that engulf and destroy pathogens.

  • Serve as guards in tissues.

• Eosinophils:

  • Target larger pathogens such as parasitic worms; tend to use enzymes more than phagocytosis.

• Natural Killer Cells:

  • A type of lymphocyte that targets cancerous and virus-infected cells.

Inflammatory Response

• Description:

  • Occurs in response to injury, helping to prevent pathogen entry.

• Mast Cells and Histamine Release:

  • Mast cells release histamine, increasing blood flow to the affected area.

  • Results in swelling, redness, and increased temperature to inhibit bacterial growth.

• Inflammatory Signs:

  • Swelling, redness, heat, and the presence of WBCs act as a defensive mechanism.

Specific Immunity

• Activation: Occurs after nonspecific responses, aiming to target specific pathogens that have breached initial defenses.

• Types of Lymphocytes:

  • B Cells: Mature in bone marrow; produce antibodies targeting antigens.

  • T Cells: Mature in thymus; involved in cell-mediated immunity.

Antigens and Antibodies

• Antigens: Molecules recognized by the immune system as foreign, triggering a response.

• Antibodies: Produced by B cells to neutralize or destroy specific antigens.

  • Antibodies are specific to pathogens; different pathogens require different antibodies.

Clonal Selection and Memory Cells

• Clonal Selection:

  • Process where specific B or T cells are cloned to attack identified pathogens.

• Memory Cells:

  • Long-lived cells that enhance response to subsequent infections by the same pathogen.

  • Result in quicker immune response and improved resistance against reinfection.

Self vs Non-Self Recognition

• Importance of distinguishing between body’s own cells and foreign pathogens.

• Autoimmune Diseases: Occur when the immune system incorrectly identifies self-cells as foreign (e.g., lupus, type 1 diabetes).

• MHC (Major Histocompatibility Complex): Molecules that help the immune system recognize self-cells, critical in organ transplants and blood transfusions.

Conclusion

• Importance of accurate immune recognition to prevent infections while avoiding autoimmunity.

• Genetic relatedness plays a role in match probability for transplants.