Lactosylceramide (LacCer) is an endogenous bioactive sphingolipid. It is expressed on the plasma membrane of human phagocytes and mediates phagocytosis, chemotaxis, and superoxide generation. LacCer forms membrane microdomains with Lyn kinase and the αi subunits of inhibitory G protein-coupled receptors, suggesting a role in cell signaling. Elevated LacCer levels in kidney cortex homogenates and urine are directly correlated with hyperglycemia, insulin resistance, and obesity in db/db transgenic diabetic mice. It promotes recruitment of CNS-infiltrating monocytes and microglia and enhances neurodegeneration in mice with chronic experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis (MS). Increased levels of LacCer in atherosclerotic plaques are correlated with increased levels of the pro-inflammatory cytokines IL-6, monocyte chemoattractant protein-1 (MCP-1), and macrophage inflammatory protein 1β (MIP-1β), as well as lipids and macrophages. LacCer is also upregulated during the secretory phase of the menstrual cycle. This product is a mixture of LacCers isolated from bovine buttermilk with variable N-acyl chain lengths.