ADHERENCE OF HAEMOPHILUS-SOMNUS TO TUMOR NECROSIS FACTOR-ALPHA-STIMULATED BOVINE ENDOTHELIAL-CELLS IN CULTURE

Vascular thrombosis and tissue infarction is a principal lesion in Hae mophilus somnus septicemia known also as thrombotic meningoencephaliti s. This study was undertaken to examine whether tumor necrosis factor- alpha (TNF-alpha) can influence the adherence of H. somnus to cultured bovine aortic endothelial cells (BAEC). Confluent BAEC were exposed t o 0-100 nM of human recombinant TNF-alpha for 12-48 h. Suspensions of different strains of H. somnus (approximately 1.5-3 x 10(8)) labelled with [methyl-H-3]-thymidine, were added to BAEC and incubated for 1.5 h, Initial studies with one pathogenic (P) strain and one nonpathogeni c (NP) strain revealed that both strains adhered to normal endothelial cells but minimally to subendothelial matrix remaining after removal of BAEC. Adherence to BAEC was reduced by an excess of unlabelled H. s omnus of the same strain. Adherence was enhanced for both strains by e xposure of BAEC to TNF-alpha in a manner that increased with TNF-alpha concentration and with duration of exposure to TNF-alpha prior to add ition of bacteria. A survey of adherence of six live P strains and six NP strains demonstrated considerable variation but no difference in a dherence between P and NP strains to normal or to TNF-alpha-stimulated BAEC. However, TNF-alpha consistently increased adhesion of each stra in to BAEC. Both P and NP strains caused more severe cytotoxic changes in TNF-alpha-treated BAEC. Tumor necrosis factor-alpha also increased adhesion of formalin-killed bacteria of P and NP strains, Killed bact eria did not cause cytotoxic changes in BAEC. These studies demonstrat e that various strains of H. somnus adhere to BAEC in culture and that adherence is enhanced by exposure of BAEC to TNF-alpha, but adherence does not correlate with pathogenicity. These studies suggest that int rinsic adhesive properties of H. somnus to BAEC do not explain clinica l pathogenicity, but provide evidence that TNF-alpha might enhance bac terial adhesion to vascular endothelium if infection is established.