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Different mediator systems in biphasic heterologous phase of anti-GBM nephritis in mice.

BACKGROUND
After the injection of rabbit anti-mouse glomerular basement membrane (GBM) antibody into normal C57BL/6J mice severe albuminuria develops, which reaches a peak at 24 h. This early albuminuria is dependent on polymorphonuclear granulocytes (PMN) and is completely absent in the congenic beige mutant strain (C57BL/6J, bg/bg), which is genetically deficient in leukocytic neutral proteinase activity. We now studied the development of anti-GBM nephritis in beige mice during the later heterologous phase.


METHODS
In untreated beige mice we assessed the albuminuria and glomerular lesions on days 1-5 after i.v. injection of anti-GBM antibody. Secondly, effector mechanisms involved in the later days of the heterologous phase were studied by substitution of whole anti-GBM antibodies by F(ab')2 fragments, by leukocyte depletion (total body irradiation), scavenging of reactive oxygen metabolites (dimethylsulfoxide treatment), and complement depletion (cobra venom factor treatment).


RESULTS
In the later part of the heterologous phase (days 2-5), when there is still no sign of autologous antibody formation, i.v. injection of anti-GBM antibodies in beige mice induces nephritis with gradually increasing albuminuria, that reaches levels similar to those in non-deficient, congenic controls by day 3. This late albuminuria did not occur after injection of F(ab')2 fragments of the antibody, could be prevented by leukocyte depletion, and was greatly reduced by treatment with dimethylsulfoxide, a scavenger of hydroxyl radicals. The late albuminuria was not influenced by complement depletion with cobra venom factor. Histologic and immunohistologic studies gave no indication for a role of glomerular macrophages or lymphocytes.


CONCLUSIONS
The heterologous phase in murine anti-GBM nephritis is a biphasic process, with sequential involvement of different and independent mediating systems: both phases are PMN-dependent, but only the early albuminuria depends on leukocytic neutral proteinase activity, whereas the albuminuria and the glomerular damage at later days are effected by reactive oxygen metabolites, most probably originating from PMN accumulating in the glomerulus.