Pasteurella haemolytica leukotoxin induces bovine leukocytes to undergo morphologic changes consistent with apoptosis in vitro.

Infection of the bovine lung with Pasteurella haemolytica results in an acute respiratory disorder known as pneumonic pasteurellosis. One of the key virulence determinants used by this bacterium is secretion of an exotoxin that is specific for ruminant leukocytes (leukotoxin). At low concentrations, the leukotoxin can activate ruminant leukocytes, whereas at higher concentrations, it inhibits leukocyte functions and is cytolytic, presumably as a result of pore formation and subsequent membrane permeabilization. We have investigated the possibility that the activation-inhibition paradox is explained in part by leukotoxin-mediated apoptosis (i.e., activation-induced cell death) of bovine leukocytes. Incubation of bovine leukocytes with P. haemolytica leukotoxin caused marked cytoplasmic membrane blebbing (zeiosis) and chromatin condensation and margination, both of which are hallmarks of apoptosis. The observed morphologic changes in bovine leukocytes were leukotoxin dependent, because they were significantly diminished in the presence of an anti-leukotoxin monoclonal antibody. In addition, bovine leukocytes incubated with culture supernatant from a mutant strain of P. haemolytica that does not produce any detectable leukotoxin failed to exhibit the morphologic changes characteristic of cells undergoing apoptosis. These observations may represent an important mechanism by which P. haemolytica overwhelms host defenses, contributing to the fibrinous pleuropneumonia characteristic of bovine pasteurellosis.

A comparison of the SSW and language test results.

The purpose of this paper is to determine the relationship between the SSW and a battery of auditory-language tests in a group of children suspected of auditory processing problems. Thirty-one children between the ages of 6.2 and 10.4 were referred by their classroom teachers. All children were administered a pure tone and an acoustic immittance battery, the SSW test, selected subtests of the Clinical Evaluation of Language Functions, the Goldman-Fristoe-Woodcock Auditory Skills Battery, an elicited language sample, and the Observational Profile of Classroom Communication. No significant correlations were found between the SSW right competing and left competing conditions and the auditory-language test battery. The findings suggest that these two test approaches measure different aspects of auditory processing abilities in children, and both are required to adequately describe auditory processing abilities at all levels.