Adaptive Immune System Summary

Definition: Adaptive immunity is a sophisticated response system that develops and matures as individuals age, providing effective elimination of pathogens.
Timeframe: It typically requires a week or more to build effective immunity following the first exposure to a pathogen.
- Note: During this period, the innate immune system provides initial protection.
Memory: Adaptive immunity possesses immunological memory, allowing for a more robust response upon re-exposure to the same pathogen. This principle is leveraged in vaccinations.
Specificity: It is specific; immunity against one pathogen does not extend to others, ensuring targeted responses.
Tolerance: The immune system can discern between “healthy self” cells and “dangerous” cells (pathogens, cancer cells).

Lymphocytes: The adaptive immune response relies mainly on two types of lymphocytes:
- B cells: Responsible for humoral immunity.
- T cells: Responsible for cell-mediated immunity.
Primary Response: The first recognition of an antigen elicits a primary response.
Secondary Response: Subsequent encounters lead to a stronger, more efficient response due to memory cells.

Function: Addresses extracellular antigens (bacteria, toxins, viruses in bodily fluids).
Mechanism:
- B lymphocytes proliferate and differentiate into plasma cells, which produce antibodies.
- Memory B cells ensure a rapid response upon future exposure.
Activation: Typically requires assistance from helper T cells (TH cells).

Function: Engages with antigens residing within host cells (e.g., viral infection).
T Lymphocytes:
- Cytotoxic T Cells (TC): Induce apoptosis in infected or cancerous cells.
- Helper T Cells (TH): Activate B cells and macrophages, coordinating the immune response.
Regulatory T Cells (Treg): Maintain tolerance to prevent autoimmune responses.

Execution of Immune Response:
- Dendritic Cells: Present antigens to activate T cells through peptide-MHC complex recognition.
- B Cells Activation: Involves binding of BCR to antigen, resulting in internalization and antigen presenting for TH cells.
- Antibody Production: Plasma cells (effector B cells) generate antibodies specific to the encountered antigen.

Definition: Antigens are molecules that elicit an immune response.
- Types: T-dependent antigens require TH cell confirmation for B cell activation; T-independent antigens activate B cells directly.
Epitopes: Distinct parts of antigens that trigger immune response; diverse in structure and function.

Structure: Y-shaped proteins (immunoglobulins) consisting of heavy and light chains.
Classes of Antibodies:
- IgM: First to respond, effective agglutination.
- IgG: Most abundant, provides long-term immunity.
- IgA: Important in mucosal immunity, found in secretions (saliva, tears).
- IgD: Role in antibody maturation.
- IgE: Involved in allergic responses and protection against parasitic infections.

Neutralization: Antibody prevents toxins/viruses from binding to host cells.
Opsonization: Antibodies enhance phagocytosis by marking pathogens.
Activation of Complement System: Leads to opsonization and cell lysis.
Antibody-Dependent Cellular Cytotoxicity (ADCC): NK cells lyse antibody-coated cells.

Clonal Selection Theory: Each B cell recognizes only a single epitope; the corresponding B cells proliferate after activation.
Formation:
- Plasma Cells: Produce antibodies against specific antigens.
- Memory Cells: Long-lived, react quickly upon re-exposure to pathogens.

Types:
- TC cells: Target and induce apoptosis in infected or cancer cells via MHC class I recognition.
- TH cells: Coordinate and activate B cells and macrophages via MHC class II.
Effector Functions: Differentiate to perform specific roles; TH cells assist in amplifying immune responses, while TC cells directly eliminate threats.