Evolution and the Non-Vertebrate Immune System

• Leukocytes:
  • Neutrophils - surrounds foreign body and digest it with enzymes
  • Eosinophils - engulfs and kills foreign bodies
  • Basophils - mediates hypersensitivity reactions
  • Monocytes - removes damaged tissues
  • Lymphocytes - group name for Natural Killer cells, T cells and B cells
  • Natural Killers - kills foreign bodies
•  Mast cells - mediate inflammatory response
• Dendritic cells - antigen presenting cells
• Erythrocytes
• Platelets

Evolutionary arm race:

• Always been attacked by other organisms
• Co-evolution occurs when adaptive changes in one organism favour selection adaptations in the other organism
• Mate choice can be influenced by physical signs of immune systems eg. brighter feathers = healthier

Internal Defence Systems

• Immunity
• Defence against invading pathogens
• Removal of aged cells and debris from damaged tissues
• Identification and destruction of abnormal/mutant cells

External Defence Systems

• Deals with predators and competitors
• Anatomic eg. spines
• Chemical eg. toxins
• Behavioural eg. escape response

Internal immunity is divided into the innate and acquired immune systems.

The Innate Immune System

• Works rapidly upon exposure to any foreign body
• Does not depend on prior exposure 
• Carried out by all animals

The Acquired Immune System

• Targets a specific foreign body following first exposure
• Delayed response
• Found in all jawed vertebrates - although recent research suggests that invertebrates may have some form of acquired immunity

THE ORGANISM MUST BE ABLE TO DISTINGUISH IT'S OWN TISSUE TO IT DOESN'T FIGHT THAT

• Barrier tissues act as first line of defence
• Second line of defence includes phagocytic cells, inflammation, encapsulation, antimicrobial peptides (eg. defensin) and opsonin proteins (tag and invader so can easily be recognised again)

Most insects do not have acquired immunity, however they do have cellular and humoral responses.

Cellular Response

• Haemopoietic tissues (found near heart - produces haemocytes)
• Fat bodies (produces immune peptides - found in locusts)

Humoral Factors

• Phenoloxidase - enzyme that helps polymerise molecules into melanin
• Lysosymes allow cell lysis to occur
• Antimicrobial proteins

• Produces melanotic nodules that limit pathogen spreading
• Respond to massive bacterial infection or multicellular organisms
• Similar to clotting in vertebrates
• Melanin forms around wounds and pathogens
• Hardening gel traps pathogens which are destoryed by humoral peptides
• However, requires a lot of energy

• Malaria parasite: Plasmodium - single celled protozoa that must incubate in the mosquito for 10-21 days
• National Institute of Allergy and Infectious Disease:
  • 2 groups of mouse blood were infected with Plasmodium
  • 1 group became infected but other didn't - placed in a room too hot for Plasmodiumto grow
  • 7 days later both groups were reinfected with Plasmodium
  • The infected group was up to 10 times better at killing Plasmodium
• Granulocytes (type of leukocytes):
  • The team found 3 times as many of these immune cells in the pre-infected group than they did in the unifected groups
  • When granulocytes detect a foreign body in a mosquito's blood, they can either kill in themselves or signal another cell to come and do the job