Temporal appearance of opsonizing antibody to Francisella tularensis: detection by a radiometabolic assay

A wild and an attenuated strain of Francisella tularensis differ in susceptibility to hypochlorous acid: a possible explanation of their different handling by polymorphonuclear leukocytes

We have previously reported that a wild strain of Francisella tularensis is much less efficiently killed by human polymorphonuclear leukocytes than is an attenuated strain. In the present study, the killing of the attenuated strain was found to be strictly oxygen dependent. The wild and the attenuated strains both induced a respiratory burst in the leukocytes. The difference between the strains in susceptibility to agents produced at the burst could be explained by a difference in susceptibility to hypochlorous acid.

Phagocytosis and killing of Francisella tularensis by human polymorphonuclear leukocytes

Bacteria of a wild strain of Francisella tularensis were less efficiently killed by human polymorphonuclear leukocytes than were bacteria of an attenuated strain. This finding was explained to some extent by a less efficient phagocytosis, but bacteria of the wild strain also seemed to be more resistant to killing after ingestion.

Demonstration of opsonizing antibodies to Francisella tularensis by leukocyte chemiluminescence

Twenty-three individuals were vaccinated with a viable attenuated strain of Francisella tularensis, and blood was collected at various time intervals during 4 weeks. To demonstrate opsonizing antibodies, a mixture of serum and vaccine bacteria was incubated, whereafter the chemiluminescence response of polymorphonuclear (PMN) leukocytes to this mixture was recorded. No opsonizing antibodies against F. tularensis were found in sera obtained before vaccination. Eleven days after vaccination, sera from nine individuals, and 21 days after vaccination, sera from all 23 individuals contained antibodies. Antibodies were demonstrated earlier with the chemiluminescent technique that with the agglutination reaction. Heat treatment (56 degrees C, 30 min) or removal of complement component C3 from immune serum reduced the chemiluminescent response of the leukocytes. A high chemiluminescent response of the leukocytes was induced by immunoglobulin G (IgG)- and IgM-enriched fractions of immune serum in the presence of complement. In the absence of complement, the IgG fraction induced a low chemiluminescent response; the IgM fraction induced no response at all.

Susceptibility of mice treated with cyclophosphamide to lethal infection with Leptospira interrogans Serovar pomona

Mice not normally susceptible to infection with Leptospira interrogans serovar pomona were rendered susceptible to lethal infections by treatment with a single dose of 300 mg of cyclophosphamide (Cy) per kg administered optimally from 4 days before to 1 day after infection. Cy-treated mice with either passively or actively acquired antibody were protected from death. Blood levels of leptospires in infected untreated and in Cy-treated mice remained similar until 2 days after infection, when untreated mice cleared the leptospires. Soon afterwards, opsonizing and agglutinating antibody appeared. Cy-treated mice given spleen cells from other normal or specifically immune mice were protected from infection. An important factor in the natural resistance of mice to leptospiral infection appears to be their capacity to produce circulating antibody within 48 to 72 h. Applications are suggested for this animal model in vaccination and protection studies.

Antibody response to Rocky Mountain spotted fever

Various techniques were compared to determine the most sensitive method for detection of rocky Mountain spotted fever antibody. A radiometabolic technique for detection of Rocky Mountain spotted fever antibody is also described. In infected monkeys, the fluorescent antibody technique yielded the earliest evidence of seroconversion; with some monkeys the microagglutination procedure was equally effective. The fluorescent antibody and microagglutination measurements showed higher titers than those for complement fixation, Weil-Felix, or the radiometabolic techniques.