COMPARISON OF THE INDIGENOUS ORAL MICROBIOTA AND IMMUNOGLOBULIN RESPONSES OF ATHYMIC (NU NU) AND EUTHYMIC (NU/(+)) MICE/

The role of the immune system in the homeostasis of indigenous oral ba cterial populations is poorly understood. In this study, we compared t he evolution of the indigenous oral microbiota of specific pathogen-fr ee athymic nude (nu/nu) BALB/c mice with that of their corresponding p henotypically normal (nu/+) littermates. We also evaluated correspondi ng salivary and serum antibody activities (IgA and IgG) against the pr edominant indigenous oral bacteria. The bacterial species recovered fr om the two mouse strains were Lactobacillus murinus. Enterococcus faec alis, Streptococcus oralis and Staphylococcus epidermidis. From 27 day s of age, nu/+ and nu/nu mice had significantly different proportions of oral bacterial populations. When the microbiota stabilized (at 40 d ays of age), the total cultivable microbiota of nu/+ mice was dominate d by L. murinus (65-85%), while that of nu/nu mice was dominated by E. faecalis (40-60%). The precise factors that alter the oral resident m icrobiota in nu/nu mice are unknown. We found that total salivary IgA levels were significantly lower in nu/nu mice, but no association were observed between the level of salivary IgA antibody against indigenou s bacteria and the proportion of these indigenous bacteria in the oral microbiota. The change in the microbiota of nude mice may have been c aused by other factors such as defects in other immune functions or co ld stress.