The objective of the present study was to evaluate the effect of immunomodulatory therapy (glucocorticoids (GC) and mycobacterium cell wall extract (MCWE)) on the endometrial gene expression of inflammatory cytokines in susceptible mares with induced infectious endometritis. Endometrial gene expression of pro- and anti-inflammatory cytokines; interleukin (IL)-1ß, IL-6, IL-8, IL-10, tumor necrosis factor (TNF)-a, IL-1 receptor antagonist (ra), acute phase protein (APP) serum amyloid A (SAA) and clinical parameters were evaluated. Five mares were classified as susceptible to persistent endometritis based on their endometrial histopathology and ability to clear an induced uterine inflammation. To investigate the effect of immunomodulatory therapy, the mares were inoculated with 10(5) colony forming units (CFU) Escherichia coli in three consecutive estrus cycles in a modified cross-over study design. Thus, each mare served as its own control and the treatment type was performed in randomized order. The effect of treatment with MCWE (1.5 mg Settle IV), dexamethasone (0.1 mg per kg IV) or no treatment was investigated. All mares were free from uterine inflammation before each E. coli inoculation. Endometrial biopsies were recovered 3, 24 and 72 h post inoculation. Relative gene-expression analyses were performed by quantitative reverse transcriptase PCR (qRT-PCR). Endometrial gene expression of inflammatory cytokines was modulated by administration of GC. Expression of proinflammatory cytokines (IL-1ß, IL-6, IL-8) and SAA was significantly lower in the GC treated group late in the study period (72 h) compared to "no treatment" and MCWE treatment. Increased expression of the anti-inflammatory cytokine IL-10 was observed 3 and 24 h after E. coli infusion and GC treatment. A significant decrease of SAA expression was observed after MCWE treatment compared to "no treatment". MCWE and GC treatment had a significant effect on the clearance of uterine pathogens and number of mares retaining fluid after E. coli infusion. The results of the current investigation suggest that GC is capable of effectively modulating the innate immune response to induced infectious endometritis in susceptible mares.