BME248 - Basics in Immunology

• Helper T cells activate B lymphocytes and cytotoxic T cells to destroy infected or abnormal cells.
• Dendritic cells are specialized phagocytic cells that process pathogens into peptides and present them on MHC molecules.
• Adaptive immunity has two arms: humoral immunity mediated by antibodies secreted into body fluids and cellular immunity involving T lymphocytes that directly attack infected cells.
• The immune system is a versatile defence system that evolved to protect higher organisms from invading pathogenic microorganisms
• The immune system consists of an enormous variety of cells and molecules that specifically recognize and eliminate a plethora of pathogens
• Cells and molecules in the immune system interact in a dynamic network
• Immune recognition involves specificity, where small differences in chemical structure are detected to eliminate non-self (when dangerous) and tolerate self (but not altered self)
• The immune system can be divided into innate immune response (primitive immune system) and adaptive immune response (specific immune response)
• Innate and adaptive immune responses operate in concert to protect the host
• Adaptive immune responses are the second line of defense and only become active when there is a challenge with an antigen (5-6 days)
• Adaptive immunity involves lymphocytes (T & B cells) and their effector molecules (antibodies, cytokines, cytotoxicity)
• Adaptive immunity exhibits a high degree of specificity for small structures in specific molecules and shows memory (secondary exposure to antigen induces quicker and higher specific response)
• Innate immunity is the first line of defense and most components (cells and molecules) are present before the onset of infection
• Innate immune system recognizes foreign patterns that are not present on host cells (not specific for a single pathogen but for a group of pathogens)
• Components of innate immunity include secretory molecules like lysozyme, interferons, and complement, as well as anatomical barriers like skin, epithelia, and intestinal movement
• Innate immune cells include phagocytes, inflammatory cells, and cytotoxic cells
• Components of adaptive immunity include lymphocytes (B and T cells) that display antigen-binding surface receptors
• B cells are responsible for humoral immunity and produce antibodies that can neutralize toxins, opsonize pathogens, agglutinate and immobilize bacteria and viruses, and confer immunity to the fetus
• T cells are responsible for cellular immunity and recognize antigens presented by antigen-presenting cells on major histocompatibility complex (MHC) molecules
• T helper cells (CD4+ T cells) secrete cytokines to promote the activation of B cells, cytotoxic T cells, macrophages, and others
• Cytotoxic T cells (CD8+ T cells) are able to kill target cells that express the relevant MHC class I molecules and foreign antigen
• Specificity in adaptive immunity is mediated by specific receptors expressed on B cells (BCR) and T cells (TCR), with diversity achieved through DNA rearrangements and clonal expansion leading to memory
• Immune memory allows for a faster and stronger response upon secondary exposure to the same antigen
• The immune system general idea

  -versatile,2 layereddefence system that evolved to protect higher organisms from invading pathogenic microorganisms- enormousvariety of cells and moleculesthat recognise and eliminate pathogens- interactions ofdynamic network
• What does an immune response require (fundamentally)

  Specificity= this means eliminating non-self (when dangerous) and tolerating self (but not altered self)-pattern recognitionplays large role in this
• In what 3 layers is the immune system divided into?

  1. Anatomic barriers= e.g skin, mucous 2.Innate immune cells= e.g macrophages, NK cells = "primitive" but recognises abnormalities in patterns3.Adaptive immunity= e.g B-cells/antibodies, T cells = "specific" since it evolves over time = genetic changes in adults is constant process
• Why is the immunity considered a 2 layer response?

  Because it starts with...

  1) the recognition of a foreign pattern which is done by innate immune system

  2) then becomes specific over time thanks to adaptive immune system
• Innate immunity

  - first line of defence

  - most components are present before onset of infection

  - Barriers (physical: skin, mucous ; chemical: low pH in stomach)

  - Phagocytic cells (macrophages, neutrophils) = cells that ingest

  - recognises foreign patterns that aren't present on host cells (not specific for single pathogen but for group of pathogens)
• Adaptive immunity


  - second line of defence

  - only becomes active when there's a challenge with an antigen (~5-6 days)

  - lymphocytes (T and B cells) and their effector molecules (antibodies, cytokines, cytotoxicity)

  - High degree of specificity (comes at a price)

  - very potent

  - exhibits "memory" (secondary exposure to antigen induces quicker and higher specific response)
• Components of Innate immune system


  -Physical= anatomical barriers -Humoral= anything in liquid/ soluble in water = usually proteins e.g lysozyme in tears -Cellular= macrophages, neutrophils, mast cells = mostly phagocytic
• Components of Adaptive immune system

  -Humoral= anything in liquid/ soluble in water = antibodies-Cellular= T-cells = recognise cell-cell interactions
• Examples of anatomical barriers of innate immunity

  - skin

  - epithelia (intestines)

  - intestinal movement

  - oscillation of broncho-pulmonary cilia

  - eyelids
• Examples of secretory molecules of innate immunity

  - organic acids in skin secretions

  - lysozyme in oro-naso-pharyngeal, lacrimal secretions and tears (breaks down bacterial wall)

  - thiocyanate in saliva

  - interferons inhibit viral replication and activate other cells
• Examples of innate immune cells

  - phagocytes (macrophage, neutrophil, dendritic cells)- inflammatory cells (neutrophils, eosinophils, basophils, mast cells, ILCs)- cytotoxic cells = A type of immune cell that can kill certain cells, including foreign cells, cancer cells, and cells infected with a virus =(NK cells)
• Humoral immunity in regards to Adaptive immunity

  - mediated by antibodies, which are produced by B cells

  - antibodies go everywhere but don't do much to pathogen, just act as markers

  - antibodies can be transferred from 1 individual to another by the fluid part (humor) of the blood e.g mom to child
• Cellular immunity in regards to Adaptive immunity

  - mediated by T cells

  - T cells can be transferred from one individual to another by the cells of the blood e.g adaptive therapy for cancer
• Lymphocytes consist of...

  B and T cells

  - these display antigen-binding surface receptors
• What do mature lymphocytes do?

  they circulate the blood and lymph, enter secondary lymphoid organs or inflamed tissue
• Kinetics of innate and adaptive immunity

  1) Innate immunity

  - Interferons magnitude increases = this confirms a viral state and inhibits viral entry = this dampens virus

  - simultaneously NK cells magnitude increases but at slower rate

  - interferons magnitude decreases, NK cells magnitude still increases = NK cells recognise infected cells and kills them (not sufficient tho)

  
  

  2) Adaptive immunity

  - NK cells magnitude decreases, simultaneously antibodies and T-cells increase = specialised response + immunity obtained

  - antibodies (created by B cells) neutralise virus = virus cant infect any new cells

  - T-cells kills remaining infected cells

  - both antibodies and T-cells magnitude decrease

  
• Innate response time

  minutes to hours (bcoz they're everywhere)