It has been discovered that administering therapeutically effective amounts of an antibiotic that kills Gram-negative bacteria, together with an anti-ceramide antibody or anti-ceramide mimetic, treats and prevents an array of diseases mediated by cytolytic T lymphocyte (CTL)-induced killing and/or by damage to endothelial microvasculature, including Radiation GI syndrome, GvHD disease, inflammatory diseases and autoimmune diseases.
