Immunostimulatory effect of salmon prolactin on expression of Toll-like receptors in Oncorhynchus mykiss infected with Piscirickettsia salmonis

In aquaculture, antibiotics are the traditional treatment used against bacterial infections. However, their use has increasingly come into question given their effects on fish and, possibly, on human health. Consequently, there is interest in developing alternative treatments aimed at stimulating the innate immune response of fish, which is the first line of defense against pathogens. In relation to this, the Toll-like receptors (TLR) aid in the selective identification of pathogens. The present study evaluated immunostimulatory activity of prolactin (PRL) hormone on expression levels of TLR1, 9, and 22, MyD88, and IL-1β during in vitro infection with the fish pathogen Piscirickettsia salmonis, in primary cultures of Oncorhynchus mykiss head kidney cells. Results indicated that PRL increased expression of TLRs and MyD88 during the first hours of bacterial infection, while a constant increase in expression was found for IL-1β. These findings suggest that PRL indirectly modulates expression of TLRs by activating expression of suppressors of cytokine signaling, thereby regulating immune response over long periods of time during bacterial infection.

Immunostimulatory effects of prolactin on TLR1 and TLR5M in SHK-1 cells infected with Piscirickettsia salmonis

The innate immune system is the first line of defense against infection by pathogens. It consists of various elements, including Toll-like receptors (TLRs), which recognize molecular patterns associated with pathogens and trigger the immune response, through activation of important transcription factors such as NF-κB, which are usually found sequestered in the cytoplasm by IκBα until it receives the release signal. Piscirickettsia salmonis causes piscirickettsiosis or salmonid rickettsial septicemia, a disease of great importance in Chile, representing 79.4% of the secondary mortality in important species such as Salmo salar, which is reflected in the Chilean economy. Prolactin (PRL) is a peptide hormone which has immunomodulating functions in mammals and some fish. Olavarría et al. (2010, J Immunol 185:3873-3883) determined its ability to increase the respiratory burst, its relationship with the JAK/STAT pathway, and the expression of interleukin IL-1β in Sparus aurata. Therefore, the present study was intended to establish a possible correlation and modulation between the signal transduction pathway of PRL (JAK/STAT), the pathways of NF-κB, and TLRs, in an infection caused by P. salmonis in salmon head kidney (SHK‑1) cells of S. salar. Stimulus with native PRL from S. salar was performed, and gene expression was analyzed for IL-1β, IκBα, TLR1, and TLR5M (membrane-bound form). In addition, the effect of PRL in the nuclear translocation of the transcription factor NF-κB and the possible involvement of JAK2 were analyzed by using a pharmacological inhibitor of this kinase. The results show a positive modulation of PRL in all analyzed genes and a significant increase in the translocation of NF-κB, recording a maximum at 2 h post-treatment, supporting the stimulatory hypothesis of PRL.

Molecular cloning of Salmo salar Toll-like receptors (TLR1, TLR22, TLR5M and TLR5S) and expression analysis in SHK-1 cells during Piscirickettsia salmonis infection

In fish, the innate immune system is the primary response against infection. Toll-like receptors (TLRs) recognize pathogens through pathogen-associated molecular patterns (PAMPs), and some target molecules of TLRs are homologous between fish and mammals. Piscirickettsia salmonis is one of the main pathogens affecting the salmon industry in Chile. Better knowledge of mechanisms underlying its invasive capacity and recognition of target cells is crucial for vaccine development. Therefore, Salmo salar L. TLR1, TLR22, membrane TLR5M and soluble TLR5S sequences were cloned, and expression kinetics were analysed by RT-qPCR in salmon head kidney cells (SHK-1) infected with three different P. salmonis preparations: alive, formaldehyde treated, extract. Clearly, all analysed TLRs were expressed and transcription level changes were revealed at 2 hpi, 12 or 16 hpi and 24 hpi depending on P. salmonis infection scheme. Increased IL1-beta expression confirmed TLR pathway response. Furthermore, significant expression modulations of several members of the TLR pathway in this in vitro model suggest that P. salmonis extract rather than formaldehyde-inactivated bacteria might strengthen the salmon immune system.

Differential response of two somatolactin genes to zinc or estrogen in pituitary of Cyprinus carpio

Environmental changes affect gene expression that we addressed in the pituitary, a central regulatory organ at the interface between the central nervous system and the endocrine system. With the aim to reveal effects of changes in the aquatic environment on the expression of hypothalamo-hypophyseal factors, we characterized somatolactin (SL) in Cyprinus carpio. SL, a fish specific pituitary hormone belonging to the prolactin (PRL) superfamily, is involved in background adaptation, osmoregulation, reproduction and fatty acid metabolism. Two sl genes, α and β, were discovered in carp and transcripts of both were detected in pituitaries. Clearly, expression of slα and slβ was modulated significantly in pituitary of male adult carp in response to treatment with ZnCl2 (Zn), but only slβ responded to 17β-estrogen (E2), relative to control carp as shown by RT-qPCR analyses. Furthermore, the amount of mRNA of related factors was assessed revealing variable effects on prl, growth hormone (gh), and factors involved in sl regulation: the pituitary transcription factor pit1 and hypothalamic pituitary adenylase cyclase activating peptide (pacap). In parallel, the physiological response of the experimental animals to Zn or E2 was confirmed by showing a significant increase of metallothionein (mt) or vitellogenin (vg) gene expression in liver, classical sentinels for exposure to heavy metal or estrogens. These data suggest that the sl genes seem to be involved in the response to Zn, as well as to estrogen, and could contribute to evaluate biological relevant changes in the aquatic environment.

Identification of the clpB and bipA genes and an evaluation of their expression as related to intracellular survival for the bacterial pathogen Piscirickettsia salmonis

Piscirickettsia salmonis is the pathogen responsible for salmonid rickettsial septicemia (SRS), a disease that affects a wide variety of marine cultivated fish species and causes economic losses for the aquaculture industry worldwide. Many in vitro studies have reported on the capacity of this microorganism to replicate in the interior of cytoplasmic vesicles from varied fish cell lines. However, the mechanisms used by this bacteria to survive, replicate, and propagate in cell lines, especially in macrophages and monocytes, are unknown. A number of studies have described the diverse proteins in pathogens such as Legionella pneumophila, Coxiella burnetii, and Francisella tularensis which allow these to evade the cellular immune response and replicate in the interior of macrophages in different hosts. Some of these proteins are the virulence factor BipA/TypA and the heat shock protein ClpB, both of which have been widely characterized. The results of the current study present the complete coding sequence of the genes clpB and bipA from the P. salmonis genome. Moreover, the experimental results suggest that during the infectious process of the SHK-1 cellular line in P. salmonis, the pathogen significantly increases the expression of proteins ClpB and BipA. This would permit the pathogen to adapt to the hostile conditions produced by the macrophage and thus evade mechanisms of cellular degradation while facilitating replication in the interior of this salmon cell line.

Broth medium for the successful culture of the fish pathogen Piscirickettsia salmonis

Piscirickettsiosis or salmonid rickettsial septicaemia (SRS) caused by Piscirickettsia salmonis constitutes one of the main problems in farmed salmonid and marine fishes. Since the first reports of the disease, it has been successfully isolated and maintained in eukaryotic cell--culture systems, but these systems are time-consuming, the media are costly, and eliminating heavily contaminated host cell debris is difficult. In this report, we describe a marine-based broth supplemented with L-cysteine, named AUSTRAL-SRS broth, that facilitates superior growth of P. salmonis strains. Strains reached an optical density of approximately 1.8 when absorbance was measured at 600 nm after 6 d incubation at 18°C. Several passages (n = 6) did not alter the culture kinetics. We report for the first time the purification of DNA, lipopolysaccharide (LPS) and whole membrane protein obtained from P. salmonis grown in this liquid medium, and thus provide a suitable platform to simplify the preparation of P. salmonis cells for genetic and serological studies. Moreover, the results of the cytopathic effect test showed that P. salmonis grown in AUSTRAL-SRS broth maintained their virulence properties, inducing apoptosis after 3 d. This makes the medium a good candidate for the successful growth of P. salmonis and an excellent basis for the development of low cost vaccines.

X-ray absorption measurements on an ultrasonic spray aerosol

Spray deposition of thin films and coatings is a widely used manufacturing process owing to its low cost, versatility and simple implementation. The objective of the presented experiments was to investigate whether X-ray absorption measurements on solutes carried by aerosols are possible, and what count rates can be achieved depending on solution flow through and the resulting mass density in the interrogation volume. The investigated prototypical spray aerosol was InCl(3) dissolved in water or ethanol dispersed via an ultrasonic nebulizer. InCl(3) spray is essential for the ion layer gas reaction process used for the deposition of In(2)S(3) buffer layers for highly efficient chalcopyrite solar cells. The discussed experiments demonstrate that measurements are possible, but that the achievement of good signal-to-noise ratios requires extended sampling times and concentrated solutions.