Probiotics and infectious diseases

There is clear evidence that certain probiotic LAB strains are able to potentiate pathogen-specific antibody responses, both in animal models and in humans. Yasui et al. (1999b) have demonstrated that mice immunized with influenza vaccine and fed Bifidobacterium breve (strain YIT4064) as a probiotic developed enhanced virus-specific antibody responses and showed greater protection against respiratory challenge than non-probiotic-fed mice. In addition, some studies have confirmed an increase in innate and lymphoid cell-mediated events in pathogen-infected mice, which may contribute to enhanced disease resistance. Shu et al. (2000) have recently shown that the probiotic B. lactis HN019 could enhance pathogen-specific antibody responses in S. typhimurium-infected mice, as well as promoting increased peritoneal cell phagocytosis and splenic lympho-proliferative potential; correlation analyses indicated that elevated immune function in probiotic-fed mice corresponded with reduced pathogen translocation in these mice and promoted enhanced survival. Other strains of bifidobacteria (such as B. breve) have been shown to increase murine antibody titres in nursing dams and to provide increased protection to weanling mice against rotavirus (Yasui et al., 1995; Fukushima et al., 1999). Recent studies have confirmed this phenomenon in weanling piglets that have been fed B. lactis HN019, which exhibit enhanced cellular and humoral immunity and increased protection against naturally acquired weanling diarrhoea (Shu et al., 2001).

In human studies, the probiotic L. rhamnosus GG has been shown to promote recovery from both rotavirus and non-bloody diarrhoea in children and infants (Raza et al., 1995; Saxelin, 1997), by reducing virus shedding as well as the duration and intensity of diarrhoeal disease (Table 13.2). Two studies have demonstrated a concomitant rise in the frequency of antibody-secreting plasma cells in the circulation of probiotic-fed children, strongly suggesting that enhanced humoral immunity plays a role in reducing convalescence time by aiding viral elimination (Kaila et al., 1992; Majamaa et al., 1995). Studies using B. breve have shown that oral administration of this probiotic to hospitalized children can also support a reduction in both the incidence of diarrhoea and of viral shedding, concomitant with elevated titres of anti-rotavirus IgA antibody in the stools (Araki et al., 1999).

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