Adaptive Immunity

• What is adaptive immunity capable of recognizing and eliminating?

  Specific foreign microorganisms and molecules

  
• What are the four characteristic attributes of adaptive immunity?

  Antigenic specificity, diversity, immunologic memory, and self/non-self recognition

  
• How does the antigenic specificity of the immune system function?

  It allows the immune system to distinguish subtle differences among antigens

  
• What can antibodies distinguish between?

  Two protein molecules that differ in only a single amino acid

  
• What does the diversity of the immune system allow it to do?

  Recognize billions of unique structures on foreign antigens

  
• What is immunologic memory in the immune system?

  It is the heightened immune reactivity upon a second encounter with the same antigen

  
• What does immunologic memory confer after an initial encounter with an infectious agent?

  Life-long immunity to many infectious agents

  
• How does the immune system normally respond to antigens?

  It responds only to foreign antigens

  
• What are the two major groups of cells involved in an effective immune response?

  T lymphocytes and antigen-presenting cells

  
• Where do T lymphocytes arise and mature?

  They arise in the bone marrow and migrate to the thymus gland to mature

  
• What do T-cell receptors recognize?

  Antigen that is bound to major histocompatibility complex (MHC) molecules

  
• What are the two major types of MHC molecules?

  Class I MHC molecules and Class II MHC molecules

  
• Which cells express Class I MHC molecules?

  Nearly all nucleated cells of vertebrate species

  
• Which cells express Class II MHC molecules?

  Only antigen-presenting cells

  
• What is T cell-mediated immunity?

  An adaptive process of developing antigen-specific T lymphocytes to eliminate infections and malignant cells

  
• What can aberrant recognition of self-antigens lead to?

  Autoimmunity

  
• How is the antigen specificity of T lymphocytes determined?

  By recognition through the T cell receptor (TCR) of unique antigenic peptides presented with MHC molecules

  
• What are naive T cells?

  Mature T lymphocytes that have not yet encountered foreign antigens and have not yet been activated

  
• Where do naive T cells circulate and reside?

  Through blood and the lymphatic system, and in secondary lymphoid organs

  
• How are antigenic peptides presented to naive T lymphocytes?

  By antigen-presenting cells in secondary lymphoid organs

  
• What ensures that naive T cells will have high affinity binding to an antigenic peptide?

  The recombinant variability of individual TCR

  
• What happens when TCR engagement occurs?

  It triggers a cascade of intracellular signaling events resulting in effector functions

  
• What are the effector functions resulting from TCR engagement?

  Cell-mediated cytotoxicity and production of various cytokines

  
• What are dendritic cells (DC) known for in the context of T cell-mediated immunity?

  They are the most efficient "professional" antigen-presenting cells

  
• How are T cells subdivided?

  Based on lineage markers and functional activities

  
• What do CD4+ cells recognize?

  Antigens in the context of MHC class II molecules

  
• What do CD8+ cells recognize?

  Antigens in the context of MHC class I molecules

  
• How can activated T cells be distinguished?

  By their functional status and phenotype expressed

  
• What are naive T cells considered in terms of homogeneity?

  They are the most homogenous representatives of CD4+ and CD8+ subsets

  
• What happens to naive T cells upon activation?

  They can be further distinguished by their cytokine profiles

  
• What cytokines do Th1 cells produce?

  IFN-γ, IL-2, TNF-α, and lymphotoxin

  
• What is the role of Th1 cells?

  Enhance cell-mediated immunity and induce delayed-type hypersensitivity

  
• What do Th2 cells secrete?

  IL-4, IL-5, IL-6, IL-10, and IL-13
• What are the two subsets of regulatory T (Treg) cells?

  Naturally arising cells (nTreg) and inducible Treg (iTreg)

  
• What happens when a naive T cell encounters an antigen combined with an MHC molecule?

  The T cell proliferates and differentiates into memory T cells and various effector T cells

  
• What is the role of Th17 cells?

  Enhance pro-inflammatory actions in diseases like rheumatoid arthritis and psoriasis

  
• What cytokine does Th17 produce that stimulates other cells?

  IL-17

  
• What does IL-22 produced by Th17 cells do?

  Co-operates with IL-17 in the induction of antimicrobial peptides

  
• What are CD8+ cytotoxic T lymphocytes derived from?

  Activated naive CD8+ cells

  
• How do CD8+ cytotoxic T lymphocytes recognize antigens?

  In association with MHC class I