Few data are available on the relationship between immune response and the infection caused by gut mucosal barrier dysfunction in patients with severe acute pancreatitis (SAP). The aim of this study was to investigate the immune response to gut mucosal barrier dysfunction in patients with early SAP. The results showed that the levels of endotoxin, the lactulose/mannitol (L/M) ratio, the D(-)-lactate concentration, the proportion of HLA-DR-positive monocytes, and the expression levels of TNF-α, IL-6 and IL-10 all decreased from a high level while the frequency of Tregs increased during the first 14 days. The Th1/Th2 ratio was decreased, with a decreased Th1 and an increased Th2 profile, in the beginning, but it was subsequently increased, with an increased Th1 profile. The data from this study showed that immunosuppression, the shift of the Th1/Th2 balance toward a Th2 response, increased Tregs, and related inflammatory cytokines are involved in the complex process of inflammation and infection caused by gut mucosal barrier dysfunction in patients with early SAP.