Establishment of a human microbiome- and immune system-reconstituted dual-humanized mouse model

Humanized mice are widely used to study the human immune system in vivo and investigate therapeutic targets for various human diseases. Immunodeficient NOD/Shi-scid-IL2rγnull (NOG) mice transferred with human hematopoietic stem cells are a useful model for studying human immune systems and analyzing engrafted human immune cells. The gut microbiota plays a significant role in the development and function of immune cells and the maintenance of immune homeostasis; however, there is currently no available animal model that has been reconstituted with human gut microbiota and immune systems in vivo. In this study, we established a new model of CD34+ cell-transferred humanized germ-free NOG mice using an aseptic method. Flow cytometric analysis revealed that the germ-free humanized mice exhibited a lower level of human CD3+ T cells than the SPF humanized mice. Additionally, we found that the human CD3+ T cells slightly increased after transplanting human gut microbiota into the germ-free humanized mice, suggesting that the human microbiota supports T cell proliferation or maintenance in humanized mice colonized by the gut microbiota. Consequently, the dual-humanized mice may be useful for investigating the physiological role of the gut microbiota in human immunity in vivo and for application as a new humanized mouse model in cancer immunology.

Creation of an experimental rearing environment for microbiome animal research using an individually ventilated cage system and bioBUBBLE enclosure

To avoid microbial contamination risk, vinyl film isolators are generally used in animal microbiome experiments involving germ-free (GF) mice and/or gnotobiotic (GB) mice. However, it can take several months to gain expertise in operating the isolator competently. Furthermore, sterilization and sterility testing, which are essential for isolator preparation, can take more than 20 days. Hence, we built an experimental rearing environment that combines an individual ventilation cage system and a bioBUBBLE clean room enclosure to easily set up an experimental animal microbiome environment for animal facilities. In this work, a three-step evaluation was conducted. First, we examined whether GF mice can be maintained in this rearing environment without bacterial contamination. Next, we examined whether GF and GB mice can be maintained without cross-contamination in one individual ventilation cage rack. Finally, we tested whether GF mice can be maintained in a biological safety cabinet controlled by negative pressure. In our series of experiments, no microbial contamination occurred over more than 3 months. These results indicated that our rearing system that combines the individual ventilation cage and bioBUBBLE systems can be used not only for experiments with GF mice but also for Biosafety Level 2 experiments that handle bacteria. Our system can mitigate various disadvantages of using vinyl film isolators. In conclusion, we established an experimental method with improved working time and efficiency compared with those of the previous vinyl isolator method.

Water avoidance stress induces visceral hyposensitivity through peripheral corticotropin releasing factor receptor type 2 and central dopamine D2 receptor in rats

BACKGROUND

Water avoidance stress (WAS) is reported to induce functional changes in visceral sensory function in rodents, but the results which have been demonstrated so far are not consistent, i.e., hypersensitivity or hyposensitivity. We determined the effect of WAS on visceral sensation and evaluated the mechanisms of the action.

METHODS

Visceral sensation was assessed by abdominal muscle contractions induced by colonic balloon distention, i.e., visceromotor response (VMR), measured electrophysiologically in conscious rats. The electromyogram electrodes were acutely implanted under anesthesia on the day of the experiment. The threshold of VMR was measured before and after WAS for 1 h. To explore the mechanisms of WAS-induced response, drugs were administered 10 min prior to the initiation of WAS.

KEY RESULTS

WAS significantly increased the threshold of VMR, and this effect was no longer detected at 24 h after. Intraperitoneal injection of astressin2 -B (200 μg/kg), a corticotropin releasing factor (CRF) receptor type 2 antagonist abolished the response by WAS. Subcutaneous (sc) injection of sulpiride (200 mg/kg), a dopamine D2 receptor antagonist blocked the response, while sc domperidone (10 mg/kg), a peripheral dopamine D2 receptor antagonist did not alter it. Naloxone (1 mg/kg, sc), an opioid antagonist did not modify it either.

CONCLUSIONS & INFERENCES

WAS induced visceral hyposensitivity through peripheral CRF receptor type 2 and central dopamine D2 receptor, but not through opioid pathways. As altered pain inhibitory system was reported to be observed in the patients with irritable bowel syndrome, CRF and dopamine signaling might contribute to the pathophysiology.

Composition of fecal microbiota of laboratory mice derived from Japanese commercial breeders using 16S rRNA gene clone libraries

The fecal microbiota of six mice derived from three Japanese commercial breeders was analyzed by using 16S rRNA gene clone libraries to construct a database for analyzing the gut microbiota of laboratory mice. The 566 clones were obtained from the clone libraries generated from the fecal DNA samples derived from BALB/c, C57BL/6N, DBA/2 and ICR mice. Among these 566 clones, there were 446 unique 16S rRNA gene sequences. When grouped at the 98% similarity level, the 446 unique sequences consisted of 103 Clostridiales, 43 Bacteroidales, 5 Lactobacillus and 3 Erysipelotricaceae, as well as sequences from 11 other phyla.

Effect of hypochlorous acid solution on the eradication and prevention of Pseudomonas aeruginosa infection, serum biochemical variables, and cecum microbiota in rats

In this study, hypochlorous acid solution, a weak acid, provided as drinking water to rats, was evaluated for its ability to eradicate and prevent Pseudomonas aeruginosa infection, while monitoring its simultaneous effect on serum biochemical variables and microbiota in the rat cecum. The results suggest that the solution could not eliminate the bacteria in the experimentally infected rats; however, the administration of a 10-parts-per-million (ppm) hypochlorous acid solution as drinking water was effective in inhibiting horizontal spread of P. aeruginosa infection among cage mates. Additionally, exposure to hypochlorous solution did not have any effect on serum biochemical variables of the rat including levels of total cholesterol, aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), albumin, total bilirubin, lipase, amylase, urea nitrogen, total protein, calcium (Ca), phosphorus (P), sodium (Na), chlorine (Cl), except for potassium (K) levels. The most frequently isolated bacteria in the rat cecum included species belonging to Bacteroidales, Lactobacillus, Clostridiales, Erysipelotrichaceae, Akkermansia, Coriobacteriales, and Firmicutes. The ratio of the terminal restriction fragment length polymorphism (T-RFLP) peaks did not differ across rats administered with 5 and 10 ppm weak acid solution as compared to the control group for any of the bacteria, except for Erysipelotrichaceae and Firmicutes, where the ratio of T-RFLP peaks was higher in the 5 ppm group for Erysipelotrichaceae and in the 10 ppm group for Firmicutes than that in the control group (P<0.01). The results suggest that the weak acid hypochlorous solution could not eradicate P. aeruginosa completely from rats. The solution was effective in preventing infection without affecting serum biochemical variables; however, some of bacterial microbiota may have changed due to administration of the solution.

Elimination of Pasteurella pneumotropica from a contaminated mouse colony by oral administration of Enrofloxacin

Enrofloxacin, a fluoroquinolone bactericidal antibiotic, was administered in an attempt to eradicate Pasteurella pneumotropica (P. pneumotropica) from a contaminated mouse colony. Contaminated mice, maintained within 4 animal rooms, were administered Enrofloxacin in drinking water at a daily dosage of 25.5 mg/kg for 2 weeks. Following one week of Enrofloxacin treatment, mice were selected randomly from each room and examined for P. pneumotropica. This procedure was repeated two or three times until all mice examined tested negative for the Pasteurella strain. With the exception of one room, treated mice consistently tested negative for P. pneumotropica for up to 45 weeks following completion of Enrofloxacin treatment. Thus, oral administration of Enrofloxacin significantly eliminated P. pneumotropica from a contaminated mouse colony.

Comparison of bacteriological, genetic and pathological characters between Escherichia coli O115a,c:K(B) and Citrobacter rodentium

Murine pathogenic Escherichia coli O115a,c:K(B) (MPEC) is the causative agent of mouse megaenteron, the pathology of which resembles that of transmissible murine colonic hyperplasia caused by Citrobacter rodentium. We compared their genetic and pathological features to reveal the relationship between these two bacteria. To evaluate the genetic distances, 16S rDNA genes were sequenced and biochemical reactions were tested. Mouse strain susceptibility tests, using CF1 MPEC-susceptible germfree mice and BALB/cA(Jic) resistant mice were performed. MPEC strains and C. rodentium showed more than 99.6% identity by comparison of 16S rDNA gene sequences. All results from biochemical reactions and the mouse strain susceptibility tests were identical. It is proposed that MPEC should be reclassified as C. rodentium.

Prophylactic effect of FK463, a novel antifungal lipopeptide, against Pneumocystis carinii infection in mice

The prophylactic effect of FK463, a new water-soluble echinocandin-like lipopeptide with inhibitory activity against 1, 3-beta-D-glucan synthase, against Pneumocystis carinii infection was investigated with the severe combined immunodeficient (SCID) mouse model. Treatment with FK463, pentamidine, and saline only was performed for 6 weeks from the day after the SCID mice were inoculated intranasally with infected lung homogenates. FK463 at 0.2 or 1.0 mg/kg of body weight, pentamidine at 4 mg/kg, or saline was subcutaneously administered daily into the backs of the SCID mice. The effects of the drugs were evaluated by detection of P. carinii cysts in mouse lung homogenates by toluidine blue O staining, lung histology, and PCR amplification of a P. carinii-specific DNA fragment from the lungs. P. carinii cysts were detected in the lungs of all mice administered saline. In contrast, no cysts were detected in mice administered both doses of FK463 and pentamidine. A specific DNA fragment was amplified from all mice administered saline and at least half or more of the mice administered FK463 and pentamidine. These results indicate that FK463 acts on cyst wall formation but not on trophozoite proliferation and is extremely effective in preventing P. carinii-associated pneumonia. These results suggest that FK463 is potentially useful as a prophylactic agent against P. carinii infection.

Evaluation of PCR as a means of identification of Pasteurella pneumotropica

A polymerase chain reaction with new primers (new PCR) designed from Pasteurella pneumotropica 16S rDNA as an identification system for this organism was compared with the PCR reported by Wang et al. (Wang's PCR) by using 15 bacterial reference species and 70 clinical isolates with the conventional identification system. For the 15 reference strains, both PCRs were identical. For the 70 clinical isolates, the new PCR and Wang's PCR showed consistency with the conventional system in 62.9% (44/70) and 51.4% (36/70), respectively. Twenty-six isolates were inconsistent with the conventional system and the new PCR with respect to morphology and serology. These findings suggested that the new PCR was more sensitive than Wang's PCR, and the new PCR in combination with morphology and serology is useful for P. pneumotropica identification.

Detection of cilia-associated respiratory bacillus in experimentally and naturally infected mice and rats by the polymerase chain reaction

Cilia-associated respiratory (CAR) bacillus was detected by means of the reverse transcription (RT)-polymerase chain reaction (PCR), and the results were compared with those of indirect immunofluorescence test (IFAT) for the detection of the organism. In the experimental infections, 15 mice were in contact with mice previously inoculated with CAR bacillus. Three mice each were tested at days 3, 5, 7, 12 and 20 postexposure. On day 3 postexposure, CAR bacillus was detected in oral swab samples from all 3 mice by RT-PCR, but was not detected in any sampling sites from the mice by IFAT. Total numbers of positive samples from nasal, oral and tracheal swabs obtained through the test were 6/15, 14/15 and 8/15, respectively, by RT-PCR, and 2/15, 6/15 and 3/15, respectively by IFAT. For the detection of CAR bacillus in samples from 52 rats, 34 serum antibody negative rats by enzyme-linked immunosorbent assay were also negative by RT-PCR and IFAT except for one sample from the oral cavity, and all serum antibody positive rats were positive for the organism by RT-PCR but it could not be detected in five of them by IFAT. By means of RT-PCR, no differences in the positive rates depending on sampling sites were observed except in one rat. The RT-PCR was found to be a specific, highly sensitive and reliable procedure for detecting CAR bacillus in mice and rats. The oral cavity was the most suitable site for the diagnosis of the early stage of this infection by RT-PCR.

Genotyping of mouse hepatitis virus strains by restriction endonuclease analysis of amplified nucleocapsid protein genes

Restriction endonuclease analysis of amplified nucleocapsid protein genes from mouse hepatitis virus (MHV) was used to differentiate 12 strains isolated from mouse liver or transplantable tumors from five facilities, and the restriction patterns of the isolates were compared with those of five well-defined MHV strains, A59, JHM, 2, S and Nu-67. The patterns of 10 isolates from three facilities were the same as that of Nu-67. The remaining two isolates revealed different patterns from the five reference strains. This study showed that reverse transcription and the polymerase chain reaction assay based restriction analysis are feasible for the detection and genotyping of MHV, and the Nu-67 related strain was the most prevalent type found in the clinical samples.