Challenges to Probiotic-Based Therapies
However, recently Lactobacillus salivarius and L fermentum strains were shown to enhance both natural and acquired immune responses, as evidenced by activation of NK cells and the expansion of Tregs, whereas Bifidobacterium infantis can induce Foxp3+ T cells that protect mice against Salmonella typhimurium infection. Therefore, it is likely both branches of the immune system contribute to LAB-induced protection against respiratory and Viagra online pathogens. In addition, a number of LAB can produce antibacterial compounds, including Lactobacillus plantarum, which can inhibit the induction of virulence factors and thus the pathogenicity of P aerogenosa, suggesting that intrinsic antibacterial effects of LAB could contribute to protection against respiratory pathogens if administered directly to the site of infection. 
Challenges to Probiotic-Based Therapies
It is likely that the antiinflammatory efficacy of a probiotic results from a combination of signaling pathways activated as a result of a specific pattern of microbe-derived ligands interacting with the corresponding receptors on host cells (Fig 2). Little is known, however, concerning the nature of the probiotic-host cell interactions, or how these interactions could be manipulated to obtain stronger regulatory responses. Factors to be considered include localization of particular bacteria in the GI tract and strain-specific cell wall components and metabolic products.
Although animal studies have provided clear evidence that certain LAB can have profound immu-noregulatory effects and regulate immune responses beyond the GI tract, the fact remains that the results of clinical trials have been highly variable. With particular regard to asthma there have been no beneficial effects reported. It is clear that candidate probiotic strains display a range of immune effects and therapeutic efficacies in specific disease states or model systems. However, strain differences are unlikely to explain all of the observed variability, as in clinical tests the same strains have produced conflicting results.
