In addition to acting as a regulator of food intake and energy expenditure, leptin can also modulate immune and inflammatory responses. The role of leptin in intestinal inflammation is the focus of the present study.

Acute and chronic colitis were induced in leptin-deficient ob/ob or wild-type (WT) mice using dextran sulfate sodium (DSS) or trinitrobenzene sulfonic acid (TNBS). The severity of colitis was evaluated, and possible mechanisms were studied.

Leptin directly stimulates intraepithelial lymphocytes (IELs) and lamina propria mononuclear cells (LPMCs). In the DSS acute model, ob/ob mice exhibited a 72% reduction of colitis severity and spontaneous release of proinflammatory cytokines from the colon compared with WT mice. Replacement of leptin in ob/ob mice converted disease resistance to susceptibility, indicating that leptin deficiency, not obesity, accounts for the resistance to acute DSS-induced colitis. During chronic DSS-induced colitis and TNBS-induced colitis, in addition to reduced disease severity, ob/ob mice exhibited a significant attenuation in intestinal inflammation, accompanied by reduced production of cytokines and chemokines. When compared with WT mice, CD8⁺ IELs of ob/ob mice were reduced in number as well as in their ability to synthesize interferon gamma. In addition, LPMCs of ob/ob mice showed increased apoptosis in untreated as well as DSS- or TNBS-treated mice. Phosphorylation of signal transducer and activator of transcription 3 and induction of cyclooxygenase 2 were absent in the colon of DSS-fed ob/ob mice.

These results show that leptin represents a functional link between the endocrine and immune systems.