immune response - 3rd line of defense 

• vaccination - infecting harmless virus in order to improve resistance
• antigen - molecule provoking a specific immune response
  • usually foreign to body
  • antigenic determinant site - parts of antigen that stimulates an immune response
• antibodies - response to antigens
  • created by B cells (made/mature in bone marrow)
  • secreted into body fluid >> humoral immunity
  • T cells (mature in thymus) directly attack the cells >> cell-mediated immunity
• exposed to pathogen, gaining immunity >> active immunity
• gaining antibodies from someone else >> passive immunity

starting the immune response - MHC proteins on cell surface 

• proteins created y major histocompatibility complex
• serves as cellular fingerprint >> body can distinguish between its cells + foreign cells >> self-versus-nonself recognition
• antigen-presenting cells - partially digests microbes, moves their antigens to the surface
  • lets T cells recognize the antigens
• MHC-I - found on all body cells
• MHC-II - found only on macrophages, B cells, and CD4+ T cells
• interleukin-1 - acts as chemical alarm signal between cells

T Cells - produces cell-mediated immune response 

• protects body from infection, cancer
• helper T-cell - detects infection, initiates B/T cell responses
• cytotoxic T-cell - detect/kill infected cells
• inducer T-cell - helps T-cells mature in thymus
• suppressor T-cell - terminates immune response after infection
• cytokines - aka lymphokines
  • regulatory molecules released by antigen-presenting cells
  • interleukin-1 - released by macrophages, stimulates helper T cells promote macrophages
  • interleukin-2 - released by helper T cells, stimulates production of cytotoxic T cells
• different MHC proteins >> higher chance for transplant rejection by immune system
• interferons currently used to stimulate immune system to fight cancer

B Cells - marks foreign microbe for destruction 

• markers activate complement proteins, macrophages, natural killer cells
• binds to free, unprocessed antibodies
• trigger antibody production in plasma cells
• able to create million to billion different antibodies through somatic DNA rearrangement

antibodies - don’t directly destroy the cell 

• IgM - 1st to be secreted during primary response, causes cells w/ antigens to stick together
• IgG - secreted in 2ndary response, major form of antibody in blood
• IgD - serves as receptors on B cell surface
• IgA - major form of antibody in saliva, milk (external secretions)
• IgE - promotes release of histamine to attack pathogen, responsible for allergies
• each consists of 2 light chains, 2 heavy chains

immunological tolerance - acceptance of a body’s own cells 

• immune system in embryo originally responds to both foreign/self molecules
• autoimmune disease - when immunological tolerance fails
  • B/T cells recognize their own tissue antigens

clonal selection - creates active immunity 

• primary immune response - generally weak due to lack of B cells
  • antigen binds to B cell >> cell division >> clones of B cells created
• 2ndary immune response - much stronger due to increase in recognition