It has been reported that splenocytes from mice orally administered
with yogurt fermented with L. bulgaricus OLL1073R-1 and S.
thermophilus OLS3059 exhibited an increase in NK cell activity [11].
In the present study, oral administration of the yogurt and EPS augmented
NK cell activity in splenocytes from influenza virus-infected
mice. In this respect, the yogurt fermented with and EPS produced
by L. bulgaricus OLL1073R-1 might augment cellular immunity, and
protect against influenza virus infection, because NK cells are lymphocytes
of the innate immune system that play a crucial role in the
early host defense against various virus infections [15,26]. The precise
mechanism responsible for the augmentation of NK cell activity is yet
to be identified; however, we assume that the EPS are taken up by
Peyer's patches in the intestine and stimulate antigen-presenting
cells, such as dendritic cells, through toll-like receptors. This would
result in selective enhancement of T-helper 1 (Th1) cell proliferation,
and the subsequent production of IL-2 and IFN-γ, which are cytokines
that are vital for cell-mediated immune responses [27]. Effects of the
yogurt and EPS for NK cell activity in the lung of influenza virusinfected
mice will be studied in the near future.