Adjuvant effect in aquaculture fish of cell-wall glycolipids isolated from acid-fast bacteria

Cell-mediated immune response against mycolic acids of Mycobacteroides salmoniphilum in rainbow trout Oncorhynchus mykiss

Mycobacteriosis caused by Mycobacterium spp. causes economic damages to the world aquaculture industry. In mammals, mycolic acids contained in the cell wall of Mycobacterium spp. are presented by CD1b molecule as lipid antigens and induce cell-mediated immunity (CMI). Here, we investigated CMI responses against the mycolic acids of Mycobacterioides salmoniphilum in a CD1-lacking teleost fish, rainbow trout. After stimulation of trout leukocytes with mycolic acids, the number and percentage of CD8α⁺ T cells increased. Fish immunized with mycolic acids showed an up-regulation of IFN-γ. Further, in vitro re-stimulation of leukocytes derived from immunized fish resulted in proliferation of CD8α⁺ cells. These data suggest that mycolic acids are recognized as lipid antigens resulting in an activation of rainbow trout CD8α⁺ cells and up-regulation of the Th1 cytokine IFN-γ. The mycolic acids are promising candidates for vaccines to activate CD8α⁺ T cells against fish mycobacteriosis.

The protective efficacy of recombinant hypoxic response protein 1 of Nocardia seriolae in largemouth bass (Micropterus salmoides)

Nocardia seriolae has become one of the major pathogens affecting the aquaculture industry and causes Nocardiosis, a highly devastating disease of marine and freshwater fish that leads to severe economic losses. Therefore, research efforts towards developing efficacious vaccines to control this disease are of high importance. In this study, the hypoxic response protein 1 (HRP1) cloned into pET32a vector was expressed, and produced in Escherichia coli strain BL21 (DE3). The antigenicity of purified recombinant TRX-tagged HRP (rHRP1) was analysed by western blotting using largemouth bass anti-N. seriolae sera. The results showed that largemouth bass anti-N. seriolae sera could specifically detect a 33 kDa rHRP1 protein. Further, the vaccine efficacy of rHRP1 was evaluated in a largemouth bass fish model by calculating the relative percent survival (RPS). rHRP1 incurred an RPS of 73.33% as compared to the control group. Immunological analysis showed that rHRP1 could produce significantly higher serum concentrations of anti-N. seriolae antibodies and serum lysozyme activity as compared to the control groups. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis showed that rHRP1 significantly enhanced the expression of immune-related genes, such as IL-12p40, IL-8, IL-1β, TNFα, IFNγ, NKEF, MHCIα, MHCIIα, CD4-1, CD8α, IgM, NF-κβ, STAT3, IRF4, RORα, and CCL20. These results indicate that rHRP1 may be a promising vaccine candidate against nocardiosis.

Elucidation of the Interleukin 12 Production Mechanism during Intracellular Bacterial Infection in Amberjack, Seriola dumerili

Intracellular bacterial infections affect all vertebrates. Cultured fish are particularly vulnerable because no effective protection measures have been established since such infections emerged approximately 50 years ago. As in other vertebrates, the induction of cell-mediated immunity (CMI) plays an important role in protecting fish against infection. However, details of the mechanism of CMI induction in fish have not been clarified. In the present study, we focused on the production of interleukin 12 (IL-12), an important factor in CMI induction in fish. Using several different approaches, we investigated IL-12 regulation in amberjack (Seriola dumerili), the species most vulnerable to intracellular bacterial disease. The results of promoter assays and transcription factor gene expression analyses showed that the expression of interferon regulatory factor-1 (IRF-1) and activator protein-1 (AP-1) is necessary for IL-12 production. Phagocytosis of living cells (LCs) of Nocardia seriolae bacteria induced IL-12 production in neutrophils, accompanied by IRF-1 and AP-1 gene expression. Bacteria in which the exported repetitive protein (Erp)-like gene was deleted (Δerp-L) could not establish intracellular parasitism or induce IRF-1 and AP-1 expression or IL-12 production, despite being phagocytosed by neutrophils. These data suggest that IL-12 production is regulated by (i) two transcription factors, IRF-1 and AP-1, (ii) phagocytosis of LCs by neutrophils, and (iii) one or more cell components of LCs. Our results enhance the understanding of the immune response to intracellular bacterial infections in vertebrates and could facilitate the discovery of new agents to prevent intracellular bacterial disease.

Vaccination of European sea bass Dicentrarchus labrax with avirulent Mycobacterium marinum (iipA::kan mutant)

Mycobacteriosis is a chronic progressive disease affecting teleost fishes all over the world. No vaccine is commercially available against its main etiological agent, Mycobacterium marinum. The mycobacterial gene responsible for invasion and intracellular persistence, iipA, is known to modulate M. marinum pathology. The innate and adaptive immune responses in sea bass (Dicentrarchus labrax) vaccinated with M. marinum iipA::kan mutant with (and without) the use of adjuvant, with (and without) a booster vaccination were monitored. The adjuvanted vaccine induced enhanced immune responses. TNF-α transcription levels were extremely high in spleen of the fish vaccinated with the addition of adjuvant in both fish vaccinated once and twice, followed by an IgM response highly specific for M. marinum. Also, histologically, granulomas started appearing in spleen and head-kidney tissues (but with no visible bacteria) within a month after vaccination, mainly with the adjuvanted vaccine. This was followed by reduction in pathology, as demonstrated by the lower number of granulomas (with visible bacteria), indicating that even heat-killed bacteria were able to elicit granulomatous formations. Adhesion of the internal organs and moderate pigmentation were observed in the perivisceral adipose tissue of nearly all vaccinated fish. Although the adjuvanted heat-killed avirulent iipA::kan mutant clearly induced a strong humoral and adaptive immune response, the booster treatment did not seem to have produced a significantly higher degree of protection from the disease compared to fish that received a single vaccination.