Bacterial viability differentially influences the immunomodulatory capabilities of potential host-derived probiotics in the intestinal epithelial cells of Atlantic cod Gadus morhua.

AIM: This study explored the effect of heat inactivation on the immunomodulatory capabilities of two potential host-derived probiotics (GP21 and GP12) on the intestinal epithelial cells (IEPC) derived from Atlantic cod. METHODS AND RESULTS: The cells were isolated from the four segments of the gut, namely anterior intestine (AI), mid-intestine (MI), posterior intestine (PI) and rectum (RC). The IEPC cultures were exposed to live or heat-inactivated form of GP21 and GP12 for 24 h. The expression profiles of bacterial defence genes and cytokine genes in the probiotics-exposed IEPCs showed differential patterns. Heat inactivation did not drastically affect the immunomodulatory properties of the probiotics, and this was explicitly typified by the stimulated expression of g-type lysozyme, hepcidin, transferrin and metallothionein in both forms of the bacteria. There was no distinct expression pattern of the interleukin genes during bacterial exposure. This was in contrast to the chemokines where the expression of these genes in IEPCs was down-regulated upon exposure to the heat-inactivated probiotics. Although heat inactivation did not drastically affect the immunomodulatory capabilities of the probiotics, the live form elicited higher immune responses in the IEPCs in most cases. CONCLUSION: This study showed that bacterial viability was a contributing influence, but not a major limiting factor on the immune-related functions of the host-derived probiotics in vitro. SIGNIFICANCE AND IMPACT OF THE STUDY: GP21 and GP12 are beneficial host-derived bacteria and could be utilized as candidate probiotics in cod aquaculture.

Truncated VP28 as oral vaccine candidate against WSSV infection in shrimp: an uptake and processing study in the midgut of Penaeus monodon.

Several oral vaccination studies have been undertaken to evoke a better protection against white spot syndrome virus (WSSV), a major shrimp pathogen. Formalin-inactivated virus and WSSV envelope protein VP28 were suggested as candidate vaccine components, but their uptake mechanism upon oral delivery was not elucidated. In this study the fate of these components and of live WSSV, orally intubated to black tiger shrimp (Penaeus monodon) was investigated by immunohistochemistry, employing antibodies specific for VP28 and haemocytes. The midgut has been identified as the most prominent site of WSSV uptake and processing. The truncated recombinant VP28 (rec-VP28), formalin-inactivated virus (IVP) and live WSSV follow an identical uptake route suggested as receptor-mediated endocytosis that starts with adherence of luminal antigens at the apical layers of gut epithelium. Processing of internalized antigens is performed in endo-lysosomal compartments leading to formation of supra-nuclear vacuoles. However, the majority of WSSV-antigens escape these compartments and are transported to the inter-cellular space via transcytosis. Accumulation of the transcytosed antigens in the connective tissue initiates aggregation and degranulation of haemocytes. Finally the antigens exiting the midgut seem to reach the haemolymph. The nearly identical uptake pattern of the different WSSV-antigens suggests that receptors on the apical membrane of shrimp enterocytes recognize rec-VP28 efficiently. Hence the truncated VP28 can be considered suitable for oral vaccination, when the digestion in the foregut can be bypassed.