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.