ABSTRACT
A number of reports have described the health-promoting effects of lactic acid bacteria (LAB) as probiotics, including the potential of LAB to affect the immune system and prevent or ameliorate respiratory tract infections such as infl uenza (Hori et al. 2002; Yasui et al. 2004; Maeda et al. 2009; Harata et al. 2010; Kawase et al. 2010; Izumo et al. 2010). Infl uenza is an acute respiratory tract infection of the infl uenza virus and is associated with a serious risk of morbidity and mortality for elderly individuals due to their weakened immune functions (Gavazzi et al. 2002). Therefore, as it is desirable to enhance the weakened immune functions of the elderly in daily life, probiotics have recently attracted a great deal of attention for this
purpose. In addition, their metabolites, extracellular polysaccharides (EPS) produced by LAB, have also been investigated and their immunostimulatory effects, such as antitumor activities (Oda et al. 1983), macrophage activation (Kitazawa et al. 1991), B-cell mitogenic activities (Kitazawa et al. 1993),and induction of cytokines (Kitazawa et al. 1996) have been reported. However, most of these studies have been performed in vitro and little information is available from the in vivo experiments involving oral administration. In this chapter, we shall describe the potential of EPS as immunogenics using the induction of the interferon-gamma (IFN-γ) production, the promotion of the natural killer (NK) cell activity, and the anti-infl uenza virus effect exerted by EPS produced from Lactobacillus delbrueckii ssp. bulgaricus (L. bulgaricus) OLL1073R-1 (Makino et al. 2006; Nagai et al. 2011). L. bulgaricus OLL1073R-1 originated in traditional Bulgarian yogurt and its EPS was shown to have some immunostimulatory effects in in vitro experiments (Kitazawa et al. 1998; Nishimura-Uemura et al. 2003; Makino et al. 2006). Yogurt fermented with this strain may contain immunostimulatory EPS as immunogenics and contribute to the maintenance of our health by reducing the risk of infection. Therefore, we also evaluated whether the intake of yogurt fermented with L. bulgaricus OLL1073R-1 improved the immune system parameters that contribute to biological defenses in the elderly and if a preventive effect occurred against respiratory tract infections, such as the common cold and infl uenza virus infection.
