Inhibition of splenic macrophage tumor necrosis factor alpha secretion in vivo by antilipopolysaccharide monoclonal antibodies

R. J. Battafarano, R. S. Burd, K. M. Kurrelmeyer, C. A. Ratz and D. L. Dunn
Department of Surgery, University of Minnesota, Minneapolis.

OBJECTIVE: This study tried to determine whether administration of antilipopolysaccharide (LPS) murine monoclonal antibody (mAb) 2A3 to mice was associated with (1) protective capacity during experimental gram-negative bacterial sepsis, and (2) inhibition of tumor necrosis factor alpha (TNF-alpha) secretion in the systemic circulation and at the tissue level during experimental infection. DESIGN: Mice received an initial intravenous injection of either saline or 100 micrograms of anti-LPS mAb 2A3, and 1 hour later underwent intraperitoneal inoculation of viable Escherichia coli 0111:B4. Mortality was assessed daily for 7 days. Separate groups of mice were treated similarly and plasma TNF-alpha concentrations were determined from blood samples obtained at 1, 3, 6, 10, and 16 hours after infection by enzyme-linked immunosorbent assay. Concurrently, splenocytes harvested from animals 3, 10, and 16 hours after infection were incubated in culture ex vivo and supernatant TNF-alpha levels were determined. RESULTS: Pretreatment with anti-LPS mAb 2A3 prior to an intraperitoneal challenge of live E coli 0111:B4 was associated with the following: (1) significant protective capacity (100% vs 0% mortality, P < .001); (2) inhibition of plasma TNF-alpha levels 16 hours after infection (1257 +/- 323 pg/mL vs 292 +/- 254 pg/mL, P < .001); and (3) abrogation of TNF-alpha secretion derived from splenic macrophages isolated 16 hours after bacterial challenge (229 +/- 12 pg/mL vs 107 +/- 48 pg/mL, P < .05). CONCLUSIONS: These results strongly support the contention that inhibition of LPS-induced TNF-alpha secretion at both the tissue and systemic levels is a key mechanism by which anti-LPS mAbs provide protection during gram-negative bacterial peritonitis. We believe that in vivo monitoring of macrophage cytokine secretion will be critical for elucidating the precise role of a variety of mediators in the pathogenesis of gram-negative bacterial sepsis.