A simple cage-autonomous method for the maintenance of the barrier status of germ-free mice during experimentation

The use of germ-free (GF) isolators for microbiome-related research is exponentially increasing, yet limited by its cost, isolator size and potential for trans-contamination. As such, current isolator technology is highly limiting to researchers engaged in short period experiments involving multiple mouse strains and employing a variety of mono-inoculated microorganisms. In this study, we evaluate the use of positive pressure Isocages as a solution for short period studies (days to 2–3 weeks) of experimentation with GF mice at multiple simultaneous conditions. We demonstrate that this new Isocage technology is cost-effective and room-sparing, and enables maintenance of multiple simultaneous groups of GF mice. Using this technology, transferring GF mice from isolators to Isocage racks for experimentation, where they are kept under fully germ-free conditions, enables parallel inoculation with different bacterial strains and simultaneous experimentation with multiple research conditions. Altogether, the new GF Isocage technology enables the expansion of GF capabilities in a safe and cost-effective manner that can facilitate the growth, elaboration and flexibility of microbiome research.

Mouse platelet-derived growth factor alpha receptor: sequence, tissue-specific expression and correlation with metastatic phenotype

High- and low-metastatic cells derived from metastatic murine tumors were screened for the differential expression of proto-oncogenes which may code for cell-surface receptors to growth factors. We found that metastatic clones of 3LL carcinoma and T10 sarcoma but not non-metastatic clones of these tumors express a 6.5-kb mRNA that is recognized by a v-fms probe containing a tyrosine kinase domain. The cloning and sequence analysis of a full-length cDNA clone corresponding to the v-fms-related 6.5-kb transcript showed that this transcript is the murine homolog of platelet-derived growth factor alpha (PDGF-alpha) receptor. The cDNA contains an open reading frame that predicts a 1089 amino acid protein. Comparison with the human and rat PDGF-alpha receptor reveals an overall amino acid sequence identity of 91% and 94% respectively. Northern blot analysis shows that this gene is preferentially expressed in the high-metastatic clones and is also selectively expressed in normal mouse tissues. Immunoprecipitation using anti-PDGF-alpha receptor serum shows that 185-kDa and 170-kDa proteins were specifically precipitated from cells of the high-metastatic D122 but not from the low-metastatic A9 cells. The possibility that overexpression of PDGF-alpha receptor in high-metastatic clones may contribute to an increase in the capacity of tumor cells to generate metastases in the lung is discussed.

The differential expression of H-2K versus H-2D antigens, distinguishing high-metastatic from low-metastatic clones, is correlated with the immunogenic properties of the tumor cells

Two clones of the 3LL Lewis lung carcinoma, a low-metastatic clone A9 and a high-metastatic clone D122, were studied for MHC expression and immunogenic properties. Using monoclonal antibodies, we demonstrated that the A9 clone expresses both the H-2Kb and the H-2Db, whereas the D122 expresses only the H-2Db, and lacks the expression of the H-2Kb encoded molecules. Cells of the low-metastatic clone A9 grew progressively in syngeneic (C57BL/6J) or in F1 mice, but were rejected in allogeneic recipients. The high-metastatic D122 grew progressively in all mouse strains tested, yet metastases were formed only in syngeneic recipients. When H-2 recombinant mice were used, the A9 again manifested a significantly greater immunogenic potency than the metastatic D122, which grew in all 4 recombinants tested. Metastases, however, were formed in B10HTG and to a lesser extent in B10A(4R), thus indicating that metastasis formation is restricted by both C57BL background and H-2Db sub region. We subsequently tested whether the higher immunogenicity of the H-2Kb-positive A9 cells is expressed also in syngeneic mice, to examine whether this could account for its low metastatic phenotype. We found that immunization by A9 cells significantly inhibited the growth of a subsequent A9 graft and even of D122, yet D122 did not retard the growth of secondary D122 or A9 cells. The increased immunogenic effect was expressed also in the generation of syngeneic cytotoxic lymphocytes by A9 but not by D122 cells. We suggest that expression of H-2K molecules on the 3LL clones, immunogenicity and the metastatic phenotype are causally related in this system.