In addition to established hallmarks of GS in macaques such as AGA and TG2 serum antibodies, chronic diarrhea, enteritis, compromised epithelial integrity (measured by ZO-1 tight junction protein expression), and/or GSE, as well as increased expression of IFN-γ by peripheral and/or intestinal lymphocytes, the following measurements were examined in this study: (1) Quantitative analysis of enteric (small intestine) apoptosis; and (2) Qualitative evaluation of IL-15 production in small intestine. Here, IL15 is linked to chronic diarrheal disease.