Ingestion and Intracellular Survival of Brucella Abortus in Human and Bovine Polymorphonuclear Leukocytes

Bovine polymorphonuclear leukocytes (PMNs) were found to be significantly more bactericidal than human PMNs against a smooth-intermediate strain of Brucella abortus (45/0), whereas there was no difference in bactericidal activity of the two kinds of PMNs against a rough strain of B. abortus (45/20). Electron microscopy of thin sections of PMNs revealed that both strains of B. abortus were readily ingested; however, the extent of degranulation was significantly less than in PMNs incubated with an extracellular parasite, Staphylococcus epidermidis. Amounts of myeloperoxidase and lactoferrin released through exocytosis by PMNs incubated with S. epidermidis were 4.7- and 1.2-fold greater, respectively, than those released from PMNs incubated with B. abortus 45/0. When azurophil and specific granules were isolated after incubation of PMNs with either B. abortus 45/0 or S. epidermidis, results showed that the extent of degranulation by both types of granules was greater in PMNs incubated with S. epidermidis than in those incubated with B. abortus 45/0. Amounts of degranulation by azurophil and specific granules were similar in PMNs incubated with either the smooth-intermediate strain 45/0 or the rough strain 45/20. Degranulation was not stimulated when glutaraldehyde-killed strain 45/0 was substituted for viable cells. These data suggest that B. abortus does not stimulate an effective level of degranulation after ingestion, as observed with extracellular parasites, and that the smooth intermediate strain 45/0 is more resistant to intraleukocytic killing system than the rough strain 45/20.