Definitions

 

Dendritic Cells

 
  • Recognize pathogens via PRRs and opsonic receptors  Engulfs them
  • After activated by antigens, these cells mature and migrate to lymph node in order to present the pathogen to the naïve T cells  This induces a protective immune response 
  • Have an exceptional role in antigen presentation but can also produce a large range of cytokines in order to control other immune cells
 

Natural Killer Cells

  • Important in controlling viral infections and tumours
  • Contain several toxic molecules in their granules such as perforin and granzymes  can induce apoptosis in virus-infected or degenerated cells that show abnormal/missing MHC expression
  • Induce cellular immune response
  • One of the first cells to produce IFN-γ induced by cytokines of macrophages and dendritic cells  The IFN-γ can activate infected macrophages
  • Can also interact with adaptive immune system – Bind to cell bound antibodies 
  • (Ex. Antibody-opsonized pathogens with Fcγ receptors  Eliminate them in an antibody-dependent cell-mediated cytotoxicity)

Eosinophils

  • Plays vital role during helminth infections
  • Can detect IgE-opsonized parasites by Fcε receptors à Release cytotoxic factors of their granules to kill the parasite

Plasmatocytes

  • - Dominant population of hemocytes of arthropods
  • - Round cells with a big cytoplasm with a high number of lysosomes and an extensive ER
  • - Functions:
    • Phagocytic
    • Produce a wide range of ECM proteins for tissue remodeling during morphogenesis
    • Secrete antimicrobial peptides (AMPs) – Ex. Cecropin A1
    • Inform fat body about the existence of infectious agents  Leads to heavy AMP response
    • Recognize parasitization

Crystal Cells

  • Only composes about 5% of the hemocytes
  • Occurs during embryonic and larval development
  • Contain a proPO system (prophenoloxidase)  Plays a role in wound healing and melanisation
     

Lamellocytes

  • Only occurs in larvae (Mostly in infected ones)  Differentiates heavily during parasitization
  • They are inducible, unlike plasmatocytes and crystal cells
  • They are flat and have adhesive properties
  • Is able to take part in cellular encapsulation of foreign bodies that are too large to be eliminated or controlled via phagocytosis
  • Able to initiate melanisation if crystal cells are not present
  • Disappear during metamorphosis  Much like crystal cells

Granulocytes

  • Contain small granules
  • Circulating hemocytes that take part in phagocytosis – less when compared with plasmatocytes
  • Mainly encapsulates foreign particles and removes self-apoptotic cells