Immunology - Lecture 11 (midterm review)

Innate Immune System Recap

• Physical barriers include epithelial and mucosal linings, mucus, and tears.
• Chemical barriers include acidic pH, enzymes, and antimicrobial peptides (AMPs).
• Microbiological barriers include the microbiota.
• Innate immune cells include macrophages, neutrophils, and natural killer (NK) cells.
• Adaptive immunity is mediated by B cells and T cells.

Pathogen Pattern Recognition and Innate Immune Cell Function

• Pattern recognition receptors (PRRs) recognize pathogen-associated molecular patterns (PAMPs) present on pathogens.
• Toll-like receptors (TLRs) recognize PAMPs on the cell surface.
• Nod-like receptors (NLRs) recognize intracellular PAMPs.
• RIG-I-like receptors (RLRs) recognize viral RNA in the cytoplasm.
• PRR signaling triggers the production of cytokines and chemokines, which activate other immune cells and initiate inflammation.

Innate Immune Cell Function

• Macrophages engulf and destroy pathogens through phagocytosis.
• Neutrophils are short-lived phagocytic cells that release antimicrobial substances.
• NK cells destroy infected cells and tumor cells.

Complement Activation and Innate Immune Cell Action

• The complement system is a group of proteins that can directly kill pathogens or enhance other immune responses.
• The alternative pathway of complement activation is triggered by the presence of pathogens on surfaces.
• Complement proteins form the membrane attack complex (MAC), which disrupts the integrity of pathogen membranes.
• Complement also enhances phagocytosis by opsonization.

The Acute-Phase Response and Complement Activation

• The acute-phase response is an early innate immune response to infection or injury.
• It involves the production of acute-phase proteins by the liver, such as C-reactive protein (CRP).
• CRP activates the classical pathway of complement activation.

The Adaptive Immune System

• The adaptive immune system is characterized by its specificity and memory.
• T cells recognize antigen presented by MHC molecules on antigen-presenting cells (APCs).
• B cells produce antibodies that recognize and neutralize pathogens.

Lymphocyte Development and Receptor Gene Recombination

• Lymphocyte development occurs in primary lymphoid tissues, such as the bone marrow and thymus.
• Recombination of receptor genes creates a vast diversity of antigen receptors.
• V(D)J recombination is a process that generates diversity in the antigen-binding sites of T cell receptors (TCRs) and B cell receptors (BCRs).

Antigen Recognition and Presentation

• MHC molecules present peptides derived from pathogens on the cell surface.
• TCRs recognize specific peptide-MHC complexes.
• BCRs bind to intact antigens.

T Cell Activation

• TCR signaling triggers the activation of T cells.
• Co-stimulatory signals, provided by molecules such as CD28, are required for full T cell activation.
• Activated T cells proliferate and differentiate into effector T cells.

B Cell Activation

• B cell activation involves antigen binding to the BCR and co-stimulatory signals.
• Activated B cells differentiate into antibody-secreting plasma cells.
• Antibody-mediated immunity is a major component of the adaptive immune response.

MHC Diversity

• MHC molecules are highly polymorphic, which contributes to the immune system’s ability to recognize a wide array of antigens.
• MHC polymorphism can influence the range of peptides bound, the conformation of the bound peptide, and the interaction of the MHC molecule with the TCR.