Blastocystis has at times been called a non-pathogenic yeast, so researchers at the University of Singapore put that claim to the test, by comparing the response of Blastocystis to the intestinal yeast Saccharomyces Boulardi. Their study reports that exposure of intestinal samples from mice to Blastocystis produces a significant amount of up-regulation of inflammatory chemicals, including interleukin 1β (IL-1β), IL-6, and tumor necrosis factor alpha (TNF-α). The study found that production of the inflammatory factors in macrophages was caused primarily by up-regulation of factor ERK in cells, as inhibition of ERK significantly suppressed both mRNA and protein expression of IL-6 and TNF-α and mRNA expression of IL-1β. Exposure of cells to Saccharomyces Boulardi did not produce that effect. The study also examined experimental animal infection with Blastocystis sp. subtype 7 on mice, and found increased rate of inflammation, but that was not statistically significant [in contrast to earlier study by El-Wakil]. The researchers suggested that pre-treatment of mice with Dextran Sulfate, which was intended to emphasize potential Blastocystis pathology, may have negated the effect of Blastocystis. The study was published in Infection and Immunity.