Inhibition of Macrophage Activity and Expression Profile of IL Genes in Goldfish after Challenge and Immunized with Aeromonas hydrophila

Research Article

J Bacteriol Mycol. 2019; 6(6): 1119.

Inhibition of Macrophage Activity and Expression Profile of IL Genes in Goldfish after Challenge and Immunized with Aeromonas hydrophila

Devia G1, Balasundaramb CH2 and Ramasamyc H3*

¹Department of Zoology, Nehru Memorial College, Puthanampatti 621 007, Tamil Nadu, India

²Department of Herbal and Environmental Science, Tamil University, Thanjavur 613 005, Tamil Nadu, India

³Department of Zoology, Pachaiyappa’s College for Men, Kanchipuram - 631 501, Tamil Nadu, India

*Corresponding author: Ramasamyc H, Department of Zoology, Pachaiyappa’s College for Men, Kanchipuram - 631 501, Tamil Nadu, India

Received: November 27, 2019; Accepted: December 26, 2019; Published: December 31, 2019


We investigate and characterized the macrophage activating and deactivating cytokines in mammalian systems about these immunoregulatory molecules in fish. We partially purified Macrophage Deactivating Factor (MDF) from mitogeninduced goldfish kidney leukocytes using gel permeation and chromatofocusing fast performance liquid chromatography (GP-FPLC and C-FPLC). The pretreated macrophages for 6 or 24 h with MDF before activation with Macrophage Activating Factors (MAF) and/or bacterial Lipopolysaccharide (LPS) exhibited a down-regulation in their NO response. However, treated with MDF on 24 h did not activation with MAF and LPS. The MDF treatment is impaired the NO response of goldfish macrophages infected with the mammalian protozoan parasite Leishmania major. Therefore, the present results suggest that MDF exhibits its inhibitory effect downstream of the converging intracellular pathways induced by LPS and/or L. major. In addition to investigate differential constitutive expression of IL-1β1, IL-1β2 and IL-6 genes in kidney, intestine, and spleen of goldfish (Carassius auratus) after challenge and immunization with Aeromonas hydrophila using real-time PCR analysis. All the tested interleukin gene mRNA expression levels higher in kidney, intestine, and spleen fish were injected with heat-killed or formalin-killed vaccines. However, most of the tissues a modest down-regulation in expressions of infected untreated fish. Therefore, our results indicate that vaccines treated fish up-regulation in expressions in tissues could be central regulatory and effector cytokine of inflammatory and antimicrobial responses.

Keywords: Aeromonas hydrophila; Carassius auratus; Macrophage activity; Interleukin genes; Vaccines


In fish, many interleukins e.g. IL-1 [1], IL-2 [2], IL-6 [3], IL-8 [4], IL-10 [5], IL-11 [6], type 1 and type 2 interferons [7], lymphotoxin β [8] have been identified and cloned. Recently, IL-1β [9] have been cloned and sequenced in rainbow trout and recombinant proteins produced to study their respective functions [10]. IL-1β is a proinflammatory cytokine gene that directly stimulating the innate immune system during later stages of infection [11]. The important role of IL-1β is activation of T and B cells [12]. The IL-1β produced as a precursor molecule is cleaved to generate a mature peptide that affects most cells and immune organ systems.

The activation of specific Pathogen Recognition Receptors (PRRs), molecular moieties pathogen-specific immune responses are coordinated and dependent present upon sub-sets of leukocytes, such as macrophages or dendritic cells. The PRRs are respond to pathogens or their Pathogen Associated Molecular Patterns (PAMPs) by the initiation of distinct transcriptomic programmes, which will dictate the cellular or tissue response [13,14]. In mammals, the host transcriptional programmes have been identified by microarray analysis for specific PAMPs to bacterial [15], viral [16], parasitic [17], and fungal infections [18]. Both macrophages and dendritic cells are initiates the immune response by secreting molecules, such as proinflammatory cytokines [19]. These arrays have been used to study the response in fish to vaccination [20] or stimulation with LPS [21].

The macrophage response to infection or activation by immune stimulants can be effectively analysed by microarray that allowing thousands of genes to be monitored for expression in parallel [22]. These microarrays employed by pathogens to evade the immune system are complex and by studying specific cell types or tissues the host defence strategies. In addition the gene expression response of T cells to PAMPs has been explored using microarrays [23]. To further characterize the response of specific cytokines have been used to stimulate human [24], murine [25], and bovine [26] macrophage cell lines. The availability of salmonid-specific gene chips [27- 29] has provided the means to begin to characterise the salmonid immune response at a global gene level both in vitro and in vivo. This technology will afford a deeper understanding of overall cellular and tissue processes during immune activation. A number of recent reports concerning PAMPs recognition [30], activated macrophage transcriptomics [29], immunomics [30,31], and genome-wide surveys [32,33] showed that fish and fish macrophages should lead to different physiological/immunological responses due to pathogens in vivo.

The head kidney can consequently integrate the neuro-immunoendocrine milieu in normal and pathological states. However, few global gene regulation studies concerning the molecular regulation of head kidney function during infection or PAMPs stimulation in salmonids [34] have been described. Although many studies have used this tissue as a primary source of macrophage-like cells the activation of the immune systems [35]. Lipopolysaccharides (LPS) is the major constituent of Gram-negative bacteria is widely used for PAMP-preparation, which induces potent immune responses. A portion of LPS molecule is primarily responsible for the endotoxic properties in animals [36,37].

Intracellular killing of microorganisms by macrophages is essential for protection against a variety of pathogens including protozoan parasites, fungi, bacteria, and viruses [38-42]. Cytokine-activated vertebrate macrophages kill these pathogens by producing a number of highly toxic molecules including Reactive Oxygen Intermediates (ROI) and Reactive Nitrogen Intermediates (RNI) [43-45]. Nitric oxide (NO ) is reactive nitrogen intermediate produced in the cytoplasm of macrophages through the enzyme catalyzed oxidation of the terminal guanido nitrogen of L-arginine [45] and freely diffuses across cell membranes to target enzymes that contain catalytically active labile iron [40]. Production of NO by activated macrophages appears to be a primitive killing mechanism since immunocytes from invertebrates such as insects and starfish have also been reported to produce NO [46,47] that activated Goldfish Macrophage Cell Line (GMCL) [48] and primary goldfish macrophages [49].

Aeromonas hydrophila is well known to cause a variety of diseases in fish including goldfish, such as haemorrhagic septicaemia, infectious dropsy, tropical ulcerative disease and fin rot leading to heavy mortality in aquaculture industry [50,51]. Various synthetic chemicals and antibiotics have been used to prevent or treat fish diseases with a partial success. Treatment with adjuvanted vaccine is one such strategy as the successful development of new vaccines. It is reliant upon the availability of adjuvants that are not only safe for the host, but also induce immune responses complementary during natural infection [52]. Immunostimulants, when used alone to increase the immunocompetence and disease resistance of fish by enhancing the nonspecific defence mechanisms [53]. The adjuvants used in vaccines preparations that activate antigen-presenting cells (e.g. macrophages) to produce more of the signal molecules (e.g. cytokines) to recruit other immune system cells [54]. However, very few reports, but there is no report in goldfish against A. hydrophila infection.

The aim of this paper to investigation is to characterize in vivo biological activities displayed by goldfish IL-1β1, IL-1β2 and IL-6 genes using an immunologically tractable model to focus special attention is mainly involved in the recruitment of leukocytes to the inflammatory foci rather than in their activation. In addition to investigate the release of cytokines from head kidney (HK) leucocytes susceptibility in fish after challenge and immunization (heatkilled and formalin-killed) with A. hydrophila in goldfish and their inhibition of macrophage activity and differential tissue expression by RT-PCR.

Materials and Methods


Healthy goldfish, Carassius auratus weighing approximately 38 g were purchased from a local fish farm in Jeju Island, South Korea and transported to the laboratory in plastic bags filled with oxygenated water. The fishes were maintained randomly into 150-L aquaria a total of 400 fish. All the fish were acclimated for 2 week under laboratory conditions (14/10 h light/dark cycle) prior to challenge or immunization. The aquaria water quality parameters were monitored during the experimental period as dissolved oxygen concentration 5.5 - 7.4 mg l-1 (Winkler’s method), pH 5.6 - 7.3, and temperature at 18 - 21°C. Fish were fed with a standard pelleted diet at 3% of their body weight twice a day during the experiment. Water of the aquarium was exchanged partially daily to remove waste feed and faecal materials.

A. hydrophila

A. hydrophila (KCTC 2358) was obtained from Korean Collection for Type Cultures (KCTC) in Daejeon, South Korea and maintained in the laboratory. Subcultures were maintained on tryptic soy agar (TSA, Sigma) in slopes at 5°C and routinely tested for pathogenesis [55], by inoculation into goldfish [56]. Stock culture in tryptic soy broth (TSB, Sigma) was stored at -70°C in 0.85% NaCl with 20% glycerol (v/v) to provide stable inoculate throughout the experiment [57]. Subculture of A. hydrophila was taken on TSA slope and harvested by TSB. The inoculated TSB was incubated for 24 h in a shaker at 30°C, and then centrifuged at 12000 g for 10 min at 4°C [57]. The supernatant was discarded and the bacterial pellet was washed three times with Phosphate-Buffered Saline (PBS) at pH 7.2. The number of A. hydrophila cells ml-1 in one day culture was enumerated using standard plate count methods on TSA plates supplemented with 5% sheep’s blood [57]. An aliquot of 25 μl of culture used in the challenge was plated on BHI agar plates and incubated for 48 h at 28°C.

Preparation of vaccines

The whole-cell bacterin was prepared by Akhlaghi et al [58] with some modifications. A. hydrophila were grown for 48 h at 28°C in TSB, and then washed with PBS for three times. Bacteria were grown to a density of approximately 1.0 x 105 viable cells ml-1. Suspensions containing bacterial cells were treated with formalin to a final concentration of 0.4% (v/v) overnight at 4°C. The suspension was centrifuged and washed three times with PBS as the initial volume, checked the sterility of bacteria and then stored at -70°C until use. The washed, Formalin-Killed bacterial Cells (FKC) were resuspended in PBS and stored at 4°C until used. Heat-Killed bacterial Cells (HKC) were obtained by subjecting the harvested cells to 100°C for 15 min. Both FKC and HKC thereafter diluted with an equal volume of Freund’s complete adjuvant (FCA; ICN Biomedicals). The vaccines were stored at 4°C until use. Before use, the vaccines were kept at room temperature. The efficiency of E-mediated killing of A. hydrophila bacteria was estimated by plating samples of appropriate dilutions of freshly harvested FKC and HKC agar [59], and results were compared with those from samples obtained prior to onset of lysis. Results indicated a 100% killing efficiency as no colony forming units (cfu) were found on plates.

Experimental design, immunization and cumulative mortality

Four groups of goldfish (n = 400), each comprising 50 fish in triplicate. Before injection, all fish were anaesthetised in tricaine methanesulfonate (MS222, Sigma) (100 mg l-1). One of the group Formalin-Killed Vaccine (FKV) was immunized against A. hydrophila by intra-pritoneal injection with 0.2 ml of Formalin-Killed Bacteria (FKB). Another group Heat-Killed Vaccine (HKV) was immunized against by intra-pritoneal injection with 0.2 ml of Heat-Killed Bacteria (HKB). After 15 days fish received same volume of FKB or HKB as a booster dose. Infected untreated group (I) were injected with 0.1 ml PBS containing A. hydrophila at a concentration of 1.0 x 105 viable cells ml-1. The Control group (C) was injected with 0.2 ml sterile PBS or FCA. Earlier the challenge dose was standardized to give 90% mortality in the infected untreated group (I). The cumulative mortality of control or experimental (each in 20 fish) were recorded daily basis for 30 days. Relative Percent Survival (RPS) was calculated by the following formula of Amend [60],

RPS (%) = 1 – ((% test mortality) x 100)) / (% control mortality)

Sample collection

The anterior kidney, spleen, and intestine tissue sample were collected in triplicate aquaria per group per treatment (control or experimental) on 30 days. Fish were anesthetized in a 100 mg l-1 solution of tricaine methanesulfonate (MS-222, Syndel) before collection of kidney leucocytes and tissue samples. Individual fish was sampled only once to avoid the influence on the assays due to multiple bleeding and handling stress on the fish. All tissue samples were rinsed in cold phosphate buffered saline (PBS, Gibco) at pH 7.2 and stored in 1-ml Trizol® (Invitrogen) frozen at -80°C in liquid nitrogen until DNA or RNA extraction. The Head Kidney (HK) leucocyte cells were subsequently removed for bioassay as described below.

Growth medium and isolation of goldfish kidney leukocytes

The complete culture growth medium contained 5% carp serum and 10% fetal calf serum (Hyclone) used in all experiments has been previously described by Neumann et al. [44]. Head kidney leukocytes were isolated from goldfish kidneys following Neumann et al. [49]. Kidneys were aseptically removed and placed into a petri dish containing ice-cold medium. Using a sterile plunger from a 3cc syringe, kidneys were gently pressed through sterile stainless steel screens to release kidney cells. Screens were rinsed with medium containing antibiotics, such as 50 μg ml-1 of gentamicin, 100 U ml-1 of penicillin, 100 μg ml-1 of streptomycin, and 50 U ml-1 of heparin. The resulting cell suspension was layered on 51% Percoll (Pharmacia) and centrifuged at 400 g for 25 min. Cells at the medium-51% Percoll interface were removed with a sterile pipette and transferred to sterile centrifuge tubes. To remove Percoll, cells were washed twice in serum-free medium and again centrifuged at 200 g for 10 min at 4°C. The viable leukocytes were enumerated using a haemocytometer after staining with trypan blue (Gibco).

Generation of in vitro-derived kidney macrophages (IVDKM)

The goldfish kidney leukocytes and macrophages secrete growth factors that induce selective proliferation and differentiation of macrophages from kidney hematopoietic tissues of the goldfish [61,62]. Cell Conditioned Medium (CCM) containing macrophage growth factors were obtained from the supernatants of 8-10 day old kidney leukocyte cultures. Kidney leukocytes (15-20 x 106 cells) were cultured in 20 ml of complete medium supplemented with 25% CCM. Cells were incubated at 20°C and fed on day 5 with 5 ml of complete medium. Cultures, 8-10 days old, were used as a source of macrophages for bioassays. Supernatants from these cultures were used as a source of CCM for establishing new macrophage cultures.

Generation of leukocyte supernatants for cytokine activity

Crude cytokine preparations were established following Neumann et al. [61]. The kidney leukocytes isolated from 25 fish were pooled and seeded in 75 cm2 tissue culture flasks at a concentration of 4 x 106 cells/ml, and incubated overnight in medium containing 2.5% carp serum and 10% fetal calf serum (Hyclone) at 20°C. Mixed leukocyte cultures were stimulated the following morning with 10 μg/ml concanavalin A (Con A, Boehringer Mannheim), 10 ng ml-1 phorbol myristate acetate (PMA, Sigma), and 100 ng ml-1 calcium ionophore A23187 (Sigma). Cultures were stimulated with these mitogens for 6h, after which the mitogens and serum were removed by washing the adherent cell layer with three changes of 20 ml Hanks Balanced Salt Solution (HBSS). The remaining adherent cell layer was given fresh serum-free medium and incubated for 72h at 20°C. Supernatants were subsequently removed, filter sterilized, and stored at -20°C until used in assays. These cytokine preparations were used as either a source of Macrophage Activating Factors (MAFs), or for isolating goldfish Macrophage Deactivating Factors (MDFs).

Characterization of MDF

Gel-permeation fast performance liquid chromatography (GPFPLC): The initial analyses of MAF and MDF activities were following Neumann et al. [61]. The cytokine preparations were concentrated by dialysis against Polyethyleneglycol (PEG) and were placed into dialysis bags (molecular weight cutoff=3.5 kD, SpectroPor) and covered in PEG flakes (MW=20 kD, Sigma). Concentration was allowed to proceed until half of the original volume remained in the dialysis bag. Samples underwent repeated half concentrate dialysis until the volume of the original crude preparation was concentrated 36-fold. The concentrated cytokine preparations were filter sterilized (0.22 mM filter, Millipore), separated into 500 ml samples, and stored at -20°C. Then the cytokine samples were fractionated according to size using a Superose 6 column (Pharmacia). GP-FPLC was carried out at 22°C using an FPLC system from LKB (Pharmacia, Bromma, Sweden). Concentrated cytokine preparations were thawed and centrifuged at 19000 g for 10 min before injecting 200 ml fractions onto the column. The running buffer used for GP-FPLC was 1x PBS (pH 7.2). All GP-FPLC fractions were collected at 2.5 min intervals into 15 ml centrifuge tubes, subsequently sterilized, and stored at -20°C until used in assays.

Chromatofocusing gel- permeation fast performance liquid chromatography (C-FPLC): Separation of GP-FPLC fractions by isoelectric focusing was performed following Neumann et al. [61]. GPFPLC fractions displaying maximal MDF activity were concentrated using microcentrifugal concentrators (Filtron; MW cutoff=3 kD). Prior to addition of MDF, the polystyrene microcentrifugal sample chamber was blocked for 30 min with 1% calf serum to prevent non-specific absorption of MDF activity. Chromatofocusing of concentrated MDF was performed using a Mono-P column (Pharmacia). The Mono-P column was pre-equilibrated with 0.025 M bis-Tris (pH 7.0, 1 M HCL) for establishment of the upper limits of the gradient. A linear descending pH gradient (7.0-4.0) was established by running a 1:10 dilution of Polybuffer 74 (Pharmacia) at a flow rate of 0.75 ml/min through the column. MDF samples (500 ml) were allowed to elute through the column for 30 min prior to initiation of the pH gradient. C-FPLC fractions were collected in 15 ml polystyrene tubes containing an equal volume of 10% calf serum (diluted in 1x PBS) in order to stabilize biological activity. Proteins bound to the Mono-P column (i.e. proteins having an isoelectric point of less than 4.0) were eluted from the column using a 2 M NaCl solution. This salt solution was injected onto the Mono-P column (5 injections of 500 ml) at flow rate of 0.25 ml/min. Protein elution was monitored by UV absorption (280 nm), and approximately 2 ml of eluted protein was collected. Of the eluent, 1 ml was stabilized by adding an equal volume of 10% calf serum (in PBS), and placed in a dialysis bag (3.5 kD cutoff, SpectroPor). This sample was dialyzed overnight in 1x PBS to remove excess salt. The serum-stabilized SE was subsequently tested for MDF activity using the NO bioassay.

Functional characterization of MDF in crude cytokine preparations

The functional analysis of GP-FPLC crude cytokine preparations was determined by pre-treating 8-10 days old IVDKM (5 x 104 cells/ well) with 25 ml of each fraction (1:3 dilution) for 6 h. Cells were subsequently activated with LPS (1 μg ml-1) and crude MAF (1:4 dilution) and NO production determined 72 h later using the Griess reaction.

MDF inhibition of activated goldfish macrophage NO responses

To assess the ability of MDF to inhibit NO production of activated macrophages, 8-10 day old IVDKM were seeded into the wells of half-area 96-well culture plates (Costar) at 5 x 104 cells/well and pretreated for 6 h with GP-FPLC fraction containing maximal MDF activity (1:3 dilution), or C-FPLC SE (1:5 to 1:160). Macrophages were subsequently activated with crude MAF (1:4) and LPS (1 μg ml- 1), LPS alone (1 and 10 μg ml-1), or infected with Leishmania major. Activated macrophages were then incubated for an additional 72h at 20°C before determination of nitrite production by the Griess reaction.

Effects of activation sequence and MDF dose on NO production

On 8-10 days old IVDKM were exposed to MDF at varying times pre- and post-activation to determine whether macrophages required pre-treatment with MDF in order to deactivate nitric oxide production by activated macrophages. Goldfish macrophages were placed in wells of half-area 96-well culture plates (5 x 104 cell/ well), and triplicate groups treated with the GP-FPLC fraction with maximal MDF activity (1:5 dilution) 24 or 6h prior to activation with MAF (1:4) and LPS (1 μg ml-1). In parallel cultures, macrophages were treated with MAF (1:4) and LPS (1 μg ml-1) for 24 h prior to addition of MDF (1:3 dilution). Then the macrophages were incubated for 72h after stimulation at 20°C before determination of nitrite production by Griess reaction. The effect of MDF dose on inhibition of NO production by goldfish macrophages was determined by plating 5 x 104 goldfish macrophages in wells of half-area 96-well culture plates and pre-treating macrophages for 6h with serial dilutions of MDF (from 1:5 to 1:160). The macrophages were subsequently activated with MAF (1:5) and LPS (1 μg ml-1) or LPS alone (1 and 10 μg ml-1) and incubated for 72h at 20°C before determination of NO production.

Nitric oxide assay

NO production by goldfish macrophages was determined indirectly using the Griess reaction [62]. A volume of 75 μl of supernatants from individual macrophage cultures was transferred to a microtitre plate and 100 μl of 1% sulfanilamide (Sigma) (dissolved in 2.5% H3PO4) followed by 100 μl of 0.1% N-naphthyl-ethylenediamine (Sigma) (dissolved in 2.5% phosphoric acid) was added to each well. The plate was allowed to sit for 2 min before the optical densities (OD 540 nm) were determined using an automated microtitre plate spectrophotometer (Biotek). The approximate concentration of nitrite in samples was determined from a standard curve generated using known concentrations of sodium nitrite.

Effects of MDF treatment on the viability

Goldfish macrophages were seeded in triplicate into 6 ml tubes at a cell density of 2.5 x 105 cells in 250 μl. Cells were pre-treated with 125 μl medium, 1x PBS at pH 7.2, or partially purified MDF for 6h. Subsequently the macrophages were activated with MAF (1:5 final dilution) and LPS (1 μg ml-1) and incubation at 20°C for 72h. The nitrite production was determined in the culture supernatants and cell number and viability by haemocytometer after staining with trypan blue (Gibco).

Isolation of total RNA and cDNA synthesis

Tissue samples were subsequently thawed and homogenized in RNAzol B (Biogenesis) on ice. Total RNA was extracted and reversed transcribed analysis were taken an equal amount (50 mg) of tissue samples was obtained separately from each tissue in three replicate to make a pool, before isolation of the RNA. Total RNA was extracted from pooled tissue (150 μg) using Trizol® (Invitrogen) in according to the manufacturer’s protocol. The total RNA was stored at -80°C until further use. The total RNA concentration and purity were determined by measuring the absorbance at 260 and 280 nm in a UV-spectrometer (Bio Rad, USA). Originally purified RNA was diluted up to 1 μg/μl concentration before synthesis of cDNA. Two micrograms of total RNA of goldfish tissues were used to synthesize cDNA from each tissue using a Superscript™ III first-strand synthesis system for RT-PCR kit (Solgent). Then the RNA was incubated with 1 μl of 50 mM oligo (dT) 20 (500 μg ml-1, Invitrogen) and 2 μl of 10 mM dNTPs (Solgent) for 10 min at 70°C. After incubation, 4 μl of 5x cDNA synthesis buffer (Solgent), 1 μl of dithiothreitol (DTT, 0.1 M, Solgent), 0.5 μl of RNase inhibitor (Solgent) (40 U/μl), and 1 μl of SuperScript™ III reverse transcriptase (15 U/μl) were added and incubated for 1h at 50°C. Then, 1 μl Diastar RNase was added to each cDNA and incubated at 50°C for 50 min. Finally, synthesized cDNA was diluted 10-fold (total 200 μl) before storing at -20°C.

mRNA expression analysis by real time PCR

PCR was carried out using different primers sets and different conditions for β-actin (positive control), IL-1β1, IL-1β2, and IL-6 genes were given in Table 1. The β-actin and IL-1β1, IL-1β2, and IL-6 PCR’s, amplifications were performed in 25 μl reactions containing the following components: 5 ml of cDNA template (diluted in water), 1 μl (25 pmol) of each primer, 2.5 ml of 10X reaction buffer (160 mM (NH4)2SO4, 670 mM Tris–HCl, pH8.8, 0.1% Tween-20, Bioline), 0.5 ml dNTP mixture (2.5 mM for each base, Bioline), 1.25 μl of 50mM MgCl2 (Bioline), 0.125 μl (0.625 U) of Taq polymerase (Bioline) and 13.625 ml of sterile H2O The components of the PCR reaction for IL 1β1, IL-1β2, and IL-6 were identical, except that 1.25 μl forward and reverse primers, 1 μl dNTP mix, 1 μl MgCl2 and 13.375 μl of H2O was used. The first PCR in each case was for β-actin, and the amount of cDNA used in each sample was titrated (between 1 and 3 μl) to give a constant product yield. The same amount of cDNA was then used for all subsequent immune gene PCR’s as a way of normalising the data in order to give a more quantitative result.