Upregulation of macrophage migration inhibitory factor (MIF) and CD74, receptor for MIF, in rat bladder during persistent cyclophosphamide-induced inflammation

The objective of this study was to determine if macrophage migration inhibitory factor (MIF) is upregulated in the bladder during persistent cystitis. MIF is a pro-inflammatory cytokine found pre-formed in the urothelium. Previous findings showed that acute bladder inflammation increased MIF release into the bladder lumen while upregulating MIF and CD74 (MIF receptor) in the bladder. Because the effects of persistent cystitis on MIF and CD74 are not known, MIF and CD74 changes in the bladder were examined after short-term (1-day) or persistent (8-day) cyclophosphamide (CYP)-induced bladder inflammation. Anesthetized male Sprague-Dawley rats received either a single CYP treatment (150 mg/kg, ip; saline, control) and examined 1 day after treatment (short-term), or repeated CYP doses (20-75 mg/ kg, ip; saline, control; every third day for 8 days) and examined after 8 days of treatment (persistent). MIF protein levels in urine and bladder were determined. In addition, Mif, CD74, and cox-2 expression in the bladder was determined. Histology verified cystitis and MIF and CD74 immunoreactivity in the bladder. Repeated CYP doses were decreased to avoid toxicity. Short-term or repeated low CYP doses (40 mg/kg; 8 days) increased urinary MIF and decreased bladder MIF amounts while upregulating bladder Mif and CD74 mRNA expression. Persistent CYP-induced bladder inflammation (even at 40 mg/kg; 8-day treatment) also upregulated other inflammatory cytokines (CCL5, IL-11, iNOS) in the bladder. Short-term and persistent (low dose) CYP cystitis are associated with markedly increased MIF release into the urine and upregulation of Mif and CD74 in bladder. This supports the hypothesis that MIF and CD74 play a significant role in both acute and persistent stages of bladder inflammation.