Animal health - the immune system and vaccines

• What is the immune system?

  complex system of cellular & molecular processes that identify self & non-self to protect body against foreign organisms
• whats involved in primary cellular ?

  lymphocytes + monocytes
• whats involved in primary molecular?

  antigens + lymphokines
• types of immunity - non-specific

   physical + biochemical barrier (skin, hair, bone, body secretion)
• non-specific immunity, components involved:

  cellular components: granulocytes, mediator cells, mononuclear cells

  humoral components: complement, natural antibody
• specific immunity

  protects against pathogens or antigens

  enhanced response when same organism or antigen is received subsequent times

  mediated by both humoral + cellular response
• non-specific / innate immune response

  antigen - independent

  immediate maximal response

  exposure results in no immunological memory

  NOT antigen - specific
• specific/adaptive immune response

   antigen - dependent

  lag time between exposure & maximal response

  exposure results in immunological memory

  antigen - specific
• cell-mediated immunity

  Physical (by cells)

  Phagocytic Cytotoxic - physically kill antigen
• cell mediated immunity - involves 3 cell types

  antigen-presenting cells (macrophage + dendritic)

  T cells (communicate with chemical messengers: lymphokines or interleukins)

  B cells (antibody production)
• humoral immunity

  
  

  biochemical antibody production

  secretions + molecules
• defence against 'streptococcus pyogenes' SP by a macrophage: antibody production

  The macrophage eats bacteria and antigens are broken down in peptides

  antigens are displayed on macrophage surface attached to MHC II molecules on surface of B cells

  Helper T cells will stimulate B cells to produce antibodies
• non-specific cellular components: Neutrophils:

  attached to capillary linings highly phagocytic can kill pathogens
• non-specific cellular components: macrophages

  most mature from of phagocyte lineage
• macrophages: functions:

  scavenge + degradation of dead tissues + cells via antigen presentationactivation for host defence against bacteria, parasites & tumour cellspresent at sites of chronic inflammationform epithelioid cells and multinucleated giant cells
• non-specific cellular components: natural killer cells

  a sub-population of lymphocytes able to kill virus-infected + tumour cells in vivo without a helper-T cell have no markers on their cell surface can attack via an antibody response
• killer cells:

  recognition = contact with a normal cell

  destruction = contact with an infected cell
• specific immune response, T cells

  TH1 - inflammatory cells TH2 - 'true' helper cells
• T cells

  Th1 (inflammatory cells) = kill pathogens residing intracellular in vesicular compartments

  Th2 (true helper cells) = stimulate B cells for antibody production

  both express CD4 antigen
• specific immune response- B cells

  produce antibodies

  
  

  Mucosal associated lymphoid tissue (MALT)
• Passive immunity in animals ? examples

  colostrumhyper immunised egg powder
• Pathogens can by-pass immune system by ?

  Hiding which manipulates the host immune system

  causing severe disease and killing the host
• what is a vaccine?

  provides assisted immunity to prevent infections

  form of pathogen-based material administered to induce protective immunity
• goal of vaccination?

  induce long-lived immunological responses
• vaccine should induce B + T cell responses
• vaccination stimulate memory cells + long-lived plasma cells
• Abs (secondary response) vaccine =

  faster and more intense due to memory T + B cells
• 
  

  importance of stimulating mucosal immunity:

  mucosa is a major route for pathogen entry into body

  Abs in mucosal secretions trap bacteria and block virus entry

  mucous blocks adherence of organisms to the epithelial surface and prevents invasion
• importance of stimulating mucosal immunity:

  Activates specialised areas in mucosal tissues:

  Gut-Associated Lymphoid Tissue (GALT)

  Bronchial-Associated Lymphoid Tissue (BALT)

  Mucosa-Associated Lymphoid Tissue (MALT)
• Types of vaccines:

  killed/inactivated vaccines

  attenuated vaccines

  sub-unit vaccines
• Killed/ inactivated vaccines

  whole pathogenic bacteria or viruses that are made non-replicating & non-infectious
• Attenuated vaccines

  live virus particles that are mutated to a non-pathogenic form, usually by rapid passage in tissue culture cells of a foreign host
• sub-unit vaccines

  purified components of a pathogen, such as a viral surface antigen, or a bacterial toxoid
• killed/inactivated vaccines: advantages

  elicit good humoral immunity

  cannot mutate or reverse to pathogenic form
• Inactivated / killed vaccines: Disadvantages

  ·       Require adjuvant formulations

  ·       Usually injected

  ·       Boosters are needed

  ·       Poor inducers of mucosal immunity

  ·       High cost (large scale culture of pathogens)

  ·       Failures in inactivation may lead to entry of infectious material
• live attenuated vaccines: advantages

  ·       Mimic natural infection = elicit systemic and mucosal immunity

  ·       Antigens = in a natural form (cross-linking with formalin can alter the structure of proteins)

  ·       Easier & cheap to produce (culture of non-pathogen strains)

  ·       Can be given via non-injection routes, e.g. drinking water
• Live attenuated vaccines: disadvantages

  ·       Possible mutation & reversion to virulence

  ·       Spread of vaccine strain infection
• use of synthetic peptides & recombinant proteins

  advantageous as there is no need to culture pathogens
• synthetic peptides

  ·       Small peptides based on a pathogen protein can raise IgG response

  ·       Often problems with immunogenicity

  ·       Under research, successful use against CSFV, Taenia ovis
• Recombinant proteins:

  ·       Whole proteins are clones & expressed in bacteria / yeast

  ·       Commercial human hepatitis B vaccine

  ·       Infectious bursal disease virus of poultry