Insight into the lymphoid organ of penaeid prawns: A review

In crustacea, the lymphoid organ (LO) is found exclusively in penaeid prawns. Other crustaceans such as crabs, lobsters and crayfish do not possess lymphoid organs. Many scientists believe that the lymphoid organ is involved in defence against invading pathogens. The discovery of immune-related genes with the LO confirms some cells have immunological roles even though these genes might be from the haemocytes within this organ. The formation of the lymphoid organ spheroid (LOS) cells has been observed in many naturally or experimentally infected penaeid prawns with viral diseases. It has been suggested that these spheroid cells constitute a major site of viral degradation. The origin and elimination mechanism of the spheroids has been debated in a number of publications. It is most likely that this cell type is produced from exocytosed granular haemocytes and eliminated to the environment rather than in situ destruction via necrosis or apoptosis.