1. Defence mechanisms in shrimps and disease control by vaccination

2. Invertebrates lack true antibodies and therefore do not have an immune memory
Like vertebrate defence systems, the shrimps also have both cellular and humoral immunity

3. Cellular components of crustacean immunity
Crustacean haemocytes :- Crustacean haemocytes have important roles in the host immune response including recognition, phagocytosis, melanization, cytotoxicity and cell-to-cell communication.

4. Classification of the haemocyte types
hyaline cells are characterised by the absence of any granules in the cell
chiefly involved in phagocytosis
semi-granular cells contain small granules
involved in early non-self recognition and active encapsulation
granular cells have large granules
Involved in storage and release of the prophenoloxidase (proPO) system and cytotoxicity.

5. Non-self recognition mechanisms:
LPS-binding proteins
Beta-1,3 glucan-binding proteins
Peptidoglycan binding proteins
Lectins /agglutinins

6. Innate immediate immune reactions
Coagulation-clotting
Transglutaminase: is involved in clotting process in shrimps.
Clotting protein
Prophenoloxidase (ProPO) - activating system
ProPO in P. monodon has been cloned and different proteins involved in the ProPO system cascade havebeen characterised.

7. Mechanisms of cellular defence in crustaceans
Phagocytosis
the process of internalisation of invading pathogens and other small foreign particles by individual blood cells.
The phagocytosis is carried out mainly by the hyaline cells.
This is the first line of defence in crustaceans against the pathogens, which invades the tissue bypassing the cuticle

8. Nodule formation
Following to the heavy load on phagocytosis, the nodule formation is activated.
In nodule formation, the microorganisms are trapped by several layers of haemocytes and subsequent melanization of the nodule.
A method of pathogen removal from circulating haemolymph of host by localisation in gills and sinuses in the hepatopancreas.

9. Encapsulation
This process is carried out by the host when the parasite is too large to be engulfed by phagocytosis.
Semi-granular cells are primarily involved in the process.
Encapsulation is mainly directed against the fungal hyphae or helminth or nematode parasites.

10. Cytotoxicity
The invertebrate blood cells can affect cytotoxic reactions resulting in the destruction of the foreign cells
Mechanism and significance remain unknown
The cytotoxic reactions are believed to be due to the direct contact of haemocytes with the invading cells

11. Cell adhesion
Cell adhesion is essential in invertebrate immunity in the cellular immune responses of encapsulation and nodule formation.
Blood cell adhesion to the infectious organism occurs when they move to and attach at a site of inflammation or infection.

12. Humoral components of crustacean immunity
Lectins (agglutinins: proteins or glycoproteins)
ProPO activating system
Antimicrobial compounds
Serine proteinase inhibitors
Clotting reaction

13. Lectins (agglutinins: proteins or glycoproteins)
potential molecules involved in immune recognition and microorganism phagocytosis through opsonization
ProPO activating system
PO is known to be associated with melanization, sclerotization and wound healing in crustaceans.
PO oxidizes phenol into quinones, which will then polymerise non-enzymatically to melanin

14. Antimicrobial compounds
The production of antimicrobial peptides represents a first-line host defence mechanism of innate immunity
penaeidins, which were isolated from the shrimp Penaeus vannamei were successful in their role as antimicrobial peptides upon microbial challenge.

15. Serine proteinase inhibitors
Arthropod haemolymph contains proteins with serine proteinase inhibitory activity. These inhibitors may exist in plasma or in haemocyte granules.
protecting their hosts from infection by pathogens or parasites.
Some may inhibit fungal or bacterial proteases

16. Clotting reaction
Prime importance of innate immune process is to seal wounds rapidly and efficiently
Clotting process is one such reaction, which is very efficient and rapid, based on a clotting protein present in plasma and a transglutaminase in blood cells.