TNF-alpha enhances colony-stimulating factor-1-induced macrophage accumulation in autoimmune renal disease

The lpr mutation on the MRL background accelerates autoimmune nephritis in which macrophage (M phi) accumulation is prominent. Renal disease is absent in other strains with lpr. TNF-alpha and CSF-1 are increased in the kidney of MRL-lpr mice with loss of renal function. We have established that CSF-1 can incite renal injury in mice with the lpr mutation, and M phi from the MRL strain hyper-respond to this growth factor. We hypothesized that TNF-alpha enhanced the M phi response to CSF-1 in MRL-lpr mice. We now report that TNF-alpha enhanced CSF-1-induced bone marrow M phi proliferation in MRL-lpr mice, and not in congenic MRL +/+, normal C3H +/+, and BALB/c, or another strain with lpr (C3H-lpr). Using a gene transfer approach to deliver CSF-1 together with TNF-alpha into the kidney, we evaluated the impact on renal injury. Tubular epithelial cells genetically modified to produce CSF-1 (CSF-1-TEC) and TNF-alpha (TNF-TEC) placed under the renal capsule caused a greater accumulation of M phi in the implant site than CSF-1-TECs alone in MRL-lpr, but not MRL +/+ mice. We noted in tissues adjacent but not distal to the implanted TECs, an increase in M phi in the interstitium and surrounding glomeruli of MRL-lpr but not MRL +/+ mice. This indicated that CSF-1 and TNF-alpha released by TECs were responsible for promoting renal pathology. Taken together, these data suggest that the simultaneous expression of TNF-alpha and CSF-1 in the MRL-lpr kidney fosters M phi accumulation. We speculate that the increase in M phi in the kidney in response to CSF-1 and TNF-alpha is responsible for the rapid tempo of autoimmune renal injury in MRL-lpr mice.