Concise Notes on Adaptive Immunity 6B

Adaptive Immune Response

  • Specific and systemic with memory.

  • Two arms: Humoral (antibody-mediated) and Cellular (cell-mediated).

Adaptive (Specific Defense) System

  • Protects against infectious agents and abnormal body cells.

  • Amplifies inflammatory response and activates complement.

Leukocytes and Lymphocytes

  • Leukocyte: General term for white blood cells (lymphocytes, neutrophils, eosinophils, macrophages).

  • Lymphocyte: Subset of leukocytes (T, B, NK cells); have variable antigen-detecting cell surface receptors.

MHC Proteins

  • Class I MHC: Found on virtually all body cells.

  • Class II MHC: Found on certain immune cells; display peptides (self-antigens).

  • In infected cells: MHC proteins display foreign antigen fragments to mobilize defenses.

Lymphocyte Activation and Proliferation

  • Only a small fraction of B or T cells recognize an antigen (1/10,000 - 1/100,000).

  • Activation leads to significant amplification (1,000 - 50,000 fold) within 1-2 weeks.

Mucosal and Cutaneous Immune System

  • GALT (gut-associated lymphoid tissue) and MALT (mucosa-associated lymphoid tissue) are part of this system.

  • Involves M cells, antigen-presenting cells, keratinocytes, and Langerhans dendritic cells.

Antigens and Antigenic Determinants

  • Substances mobilizing adaptive defenses, typically large, complex, and non-self.

Antibody Protective Mechanisms

  • Agglutination: Enhances phagocytosis and reduces the number of infectious units.

  • Opsonization: Coating antigen with antibody enhances phagocytosis

  • Neutralization: Blocks adhesion of bacteria and viruses to mucosa, and blocks active site of toxin

  • Complement activation: Cell lysis and inflammation

  • Antibody-dependent cell-mediated cytoxicity: Antibodies attached to target cell cause destruction by non-specific immune system cells

Antibody Isotypes

  • IgA: Mucosal, secretory.

  • IgD: Surface of B cells.

  • IgE: Allergy, anaphylaxis, epithelial surfaces.

  • IgG: Major systemic immunity, memory responses.

  • IgM: Major systemic immunity, primary response, agglutination.

Convalescent Sera

  • Contains virus-neutralizing antibodies from recovered patients.

  • Used for prophylaxis or therapy but does not stimulate memory cells.

Antibody-Dependent Cellular Cytotoxicity

  • NK cells use antibodies on infected cells for identification and attachment, releasing perforins.

Humoral Immunity

  • Active: Response to infection (naturally acquired) or vaccination (artificially acquired).

  • Passive: Antibodies from mother to fetus/infant (naturally acquired) or injection of immune serum (artificially acquired); immediate protection without immunological memory.

Apoptosis

  • Programmed cell death essential for lymphocyte regulation and preventing infection spread.

Lymphocytes

  • B cells: Humoral immunity.

  • T cells: Cell-mediated immunity.

  • Antigen-presenting cells (APCs): Auxiliary roles in immunity.

T Cell Receptors and Glycoproteins

  • T cell antigen receptors recognize specific antigens.

  • CD4 and CD8 glycoproteins mediate T cell interactions.

T Cell-Mediated Immunity

  • Essential for clearing viral infections.

  • Cytotoxic T lymphocytes (CTLs) form immunological synapses with target cells for lysis.

Clonal Selection

  • B and T cells encountering stimulating antigen proliferate into large groups.

Antibody Diversity

  • Generated through somatic recombination, hypermutation, and class switching.

Humoral Immunity: Primary vs. Secondary Response

  • Primary: Initial encounter with antigen.

  • Secondary: Subsequent challenge by the same antigen results in a more rapid response due to memory cells.

Immunological Memory

  • Maintained without re-exposure to the virus.

Memory T Cells

  • Effector memory (TEM): Circulating

  • Central memory (TCM): Non-circulating

  • Resident memory (TRM)

Adaptive Defenses

  • Humoral: Antibodies defend against extracellular pathogens.

  • Cell-mediated: T cells defend against intracellular pathogens and cancer by lysing infected or cancerous cells.