Transcript 2

Leukocytes (White Blood Cells): Key players in the immune system, involved in identifying and eliminating pathogens.
MHC Class I: All healthy cells display small protein fragments on MHC Class I molecules, signaling their normal function to leukocytes.
- Altered Self Cells: Cells infected by viruses or those that are cancerous may display no MHC Class I or an abnormal version of it.

Function: NK cells target altered self cells (cancerous or virus-infected) by recognizing abnormal displaying of MHC Class I.
Mechanism: Induce apoptosis (programmed cell death) in abnormal cells rather than phagocytosis, due to size similarity with leukocytes.

Apoptosis: A controlled, orderly process of cell death; prevents damage to surrounding tissue.
All cells have innate instructions for apoptosis to protect the organism from malfunctioning cells.

Definition: A complicated system of proteins in the blood that leads to pathogen lysis through an attack complex formation.
- Does not discriminate specifically for pathogens, under the innate immune response category.
Functions:
- Forms pores in pathogen membranes leading to cell death.
- Works alongside both innate and adaptive immune responses.

Definition: A slower response that targets specific threats, involving B cells and T cells.

Location: Mature in the bone marrow (B for bone).
Function: Responsible for the humoral immune response by producing antibodies.
Antibodies: Large Y-shaped proteins that bind specifically to antigens.
- Definition of Antigen: Any substance that can bind to an antibody.
- Epitopes: Specific parts of antigens that antibodies bind to.

Y-Shaped Structure: Comprised of multiple polypeptide chains.
Binding Capabilities: Each antibody binds to its unique epitope on an antigen, enabling specific recognition among millions of possible antigens.
Genetic Rearrangement: Produces diversity in B cells, allowing unique antibodies for vast antigen variety.

Activation Process:
- B cells bind their specific antigens; require help from Helper T Cells for full activation.
- Upon activation, B cells proliferate into plasma cells which secrete large amounts of antibodies.

Neutralization: Antibodies prevent viruses and toxins from binding to host cells.
Opsonization: Tags pathogens for phagocytosis by macrophages.
Complement Activation: Antibodies can trigger the complement system to destroy pathogens.

Definition: A single antibody binding to different but similar epitopes on antigens.
- Can be beneficial (e.g., immunity to similar pathogens) or harmful (e.g., autoimmune responses).

Function: Responsible for cell-mediated immunity, do not produce antibodies.
T Cell Receptors: Unique receptors that bind to specific epitopes, embedded in the cell membrane.
Types of T Cells:
- Helper T Cells: Activate immune responses and assist B cells in antibody production.
- Regulatory T Cells: Prevent unnecessary immune responses to harmless antigens.
- Cytotoxic T Cells: Cause apoptosis in infected or cancerous cells, recognizing specific epitopes presented by MHC Class I.

Formation: Post-infection or post-vaccination, some B and T cells become memory cells.
- Function: Provide a rapid and robust response upon re-exposure to the same antigen, leading to a faster secondary immune response.

Hypersensitivity: Maladaptive immune responses toward harmless antigens, includes allergies.
Autoimmunity: Immune response against self-antigens, resulting in diseases such as multiple sclerosis and type 1 diabetes.
- Highlight the importance of correct immune system education to prevent attacks on the self.

This lecture addressed critical components and functions of the innate and adaptive immune systems, focusing on leukocyte types, immune responses, and the implications for health and disease.