march 31 lesson 12

The immune system consists of two main types of responses: humoral immunity and cell-mediated immunity.

Definition: Involves B cells that recognize and respond to antigens in body fluids or blood.
B Cells: These are white blood cells that can recognize extracellular microbes directly.
- Produce antibodies that eliminate pathogens.
- Involved in immunological memory, meaning they can remember pathogens for quicker responses in future encounters.
Pathogen Recognition: B cells recognize intact antigens (foreign substances that trigger an immune response).
Types of Antigens for B Cells:
- Exogenous (external to the body)
- Antigens can include bacteria, viruses, fungi, pollen, food, and drugs.

Definition: Involves T cells which require another cell (antigen-presenting cells like dendritic cells) to become active.
T Cells Types:
- Helper T Cells (CD4): Activate other immune cells and help differentiate B cells and cytotoxic T cells.
- Cytotoxic T Cells (CD8): Directly kill infected cells displaying antigens on MHC class I.
T cells primarily respond to intracellular pathogens (pathogens that have infected the cell).

Definition: Anything that can be recognized by immune receptors; can be self or foreign.
Antigenic Determinants: Specific parts of antigens that are recognized by antibodies or immune cells.
Exogenous vs. Endogenous Antigens:
- Exogenous: Derived from pathogens outside the cell (e.g., bacterial surface proteins).
- Endogenous: Result from pathogens that have infected the cells (e.g., viral peptides).
- Autoantigens: Normal body components that can trigger an immune response (leading to autoimmune diseases).

Function: Antigen-presenting cells that play a crucial role in activating T cells by presenting antigens.
Mechanism: They engulf pathogens during innate immunity and travel to lymph nodes to display the antigens to both B and T cells.
Present antigens on MHC class II molecules to helper T cells, leading to their activation.

Adaptive Immunity: T cells and B cells boost the response against pathogens and interact with innate immunity (e.g., macrophages, natural killer cells).
Inflammation: Triggered by immune responses, resulting in the recruitment of immune cells to the site of infection.
Cytokine Signaling: Helper T cells secrete cytokines to enhance immune responses and facilitate communication between immune cells.

Lymphocytes: B and T cells originate from hematopoietic stem cells in the bone marrow.
Naive T Cells: These are not yet activated but can differentiate into various T cells upon encountering their specific antigen presented by MHC.
- Activation Tests: New T cells must recognize MHC; those that don’t are eliminated to prevent autoimmunity.
- Important Markers: CD4 for helper T cells and CD8 for cytotoxic T cells.

Humoral Response: Involves B cells targeting pathogens outside cells via antibodies.
Cell-Mediated Response: Targets infected or cancerous cells using T cells; essential for controlling intracellular pathogens.
Memory Cells: Both B and T cells can form memory cells after activation, leading to faster responses on re-exposure to the same antigens.

Mastering the immune response involves understanding how different cells interact and how they recognize diverse antigens through various MHC pathways. Dendritic cells serve as crucial connectors between innate and adaptive immune responses.