Bacillus anthracis-derived edema toxin (ET) counter-regulates movement of neutrophils and macromolecules through the endothelial paracellular pathway
1 Southern Arizona Veterans Affairs Health Care Systems, 3601 S 6th Ave, Mail Code 111-1, Building 2, 4th floor, Tucson AZ 85723, USA
2 Center for Vaccine Development, University of Maryland School of Medicine, 685 West Baltimore St, Health Science Facility 1, Rm 480, Baltimore, Maryland 21201, USA
3 Department of Epidemiology and Public Health, University of Maryland School of Medicine, 660 West Redwood St, Howard Hall, Rm 114A, Baltimore, Maryland 21201, USA
4 Mucosal Biology Research Center, University of Maryland School of Medicine, Health Science Facility 2, Room 303D, Baltimore, Maryland 21201, USA
BMC Microbiology 2012, 12:2 doi:10.1186/1471-2180-12-2Published: 9 January 2012
A common finding amongst patients with inhalational anthrax is a paucity of polymorphonuclear leukocytes (PMNs) in infected tissues in the face of abundant circulating PMNs. A major virulence determinant of anthrax is edema toxin (ET), which is formed by the combination of two proteins produced by the organism, edema factor (EF), which is an adenyl cyclase, and protective antigen (PA). Since cAMP, a product of adenyl cyclase, is known to enhance endothelial barrier integrity, we asked whether ET might decrease extravasation of PMNs into tissues through closure of the paracellular pathway through which PMNs traverse.
Pretreatment of human microvascular endothelial cell(EC)s of the lung (HMVEC-L) with ET decreased interleukin (IL)-8-driven transendothelial migration (TEM) of PMNs with a maximal reduction of nearly 60%. This effect required the presence of both EF and PA. Conversely, ET did not diminish PMN chemotaxis in an EC-free system. Pretreatment of subconfluent HMVEC-Ls decreased transendothelial 14 C-albumin flux by ~ 50% compared to medium controls. Coadministration of ET with either tumor necrosis factor-α or bacterial lipopolysaccharide, each at 100 ng/mL, attenuated the increase of transendothelial 14 C-albumin flux caused by either agent alone. The inhibitory effect of ET on TEM paralleled increases in protein kinase A (PKA) activity, but could not be blocked by inhibition of PKA with either H-89 or KT-5720. Finally, we were unable to replicate the ET effect with either forskolin or 3-isobutyl-1-methylxanthine, two agents known to increase cAMP.
We conclude that ET decreases IL-8-driven TEM of PMNs across HMVEC-L monolayers independent of cAMP/PKA activity.