PROBLEM: Neonatal mice nursed by dams lacking immunoglobulins (Igs) may often suffer from lethal runting if raised under conventional conditions. The present study was performed in order to clarify a) the cause of the wasting syndrome and b) the protective role of antigen-specific milk antibodies.
METHOD: Ig-deficient mouse embryos in a conventional environment were embryo-transferred to specified pathogen free (SPF) dams. Neonatal growth, mortality, and health status of mice from both environments was recorded. Suspected presence of mouse hepatitis virus (MHV) was tested by RT-PCR. Protective effects on neonatal mortality of milk containing different titers of anti-MHV antibodies were investigated in cross-fostering experiments.
RESULTS: The SPF colony of Ig-deficient mice exhibited no breeding problems, whereas Ig-deficient neonates in the conventional environment suffered from lethal wasting syndrome. Serological screening of the mice kept in the two environments revealed that mice in the conventional room had high titers of antibodies against mouse hepatitis virus. Presence of MHV in runting neonates was confirmed by pathological examinations and RT-nested-PCR using MHV genome specific primers. Milk containing high titers of anti-MHV antibodies, when provided for 8 days or more, completely prevented Ig-deficient neonates from developing wasting syndrome in the conventional environment.
CONCLUSION: These findings show that the neonatal wasting syndrome is associated with the presence of MHV and that neonates are efficiently protected by MHV-specific antibodies in the milk.