Genetic Differences Between N and J Sub-Strains of C57BL/6 Mice Critically Affect Multiple Immune Responses and Their Microbiota.

Background: Within decades of breeding, the common laboratory mouse strain C57BL/6 (B6) divided into various sub-strains with B6J and B6N being most frequently used. Recent studies showed significant genetic differences affecting several physiological, biochemical, and behavioral properties. In the immunology field, however, differences between these strains have barely been characterized and the necessity to use the adequate B6 sub-strain as experimental control appears largely unrecognized.

Methods: B6J and B6N mice were tested for a potential impact of their genetic background in various immunological models including experimental antibody-mediated immune-thrombocytopenia (ITP), B-cell depletion, K/BxN arthritis model, models of acute pneumonia, and dextran sulfate sodium (DSS)-induced colitis. Additionally, gut microbiota composition was analyzed in both healthy animals and in the context of DSS colitis.

Results: B6J and B6N mice performed equally in experimental antibody-mediated immune-thrombocytopenia and B-cell depletion. However, they revealed pronounced differences in the K/BxN arthritis model as well as in models of acute pneumonia and DSS-induced colitis. Furthermore, the B6 sub-strains demonstrated remarkable differences in gut microbiota composition that were detectable already in healthy animals and became augmented in the context of DSS colitis.

Conclusion: These findings mandate that researchers must specify and match B6 sub-strain backgrounds in immunological studies to ensure reproducibility and avoid misinterpretation of genetic modifications' effects.