Binding and activation of host plasminogen on the surface of Francisella tularensis.

BACKGROUND: Francisella tularensis (FT) is a gram-negative facultative intracellular coccobacillus and is the causal agent of a life-threatening zoonotic disease known as tularemia. Although FT preferentially infects phagocytic cells of the host, recent evidence suggests that a significant number of bacteria can be found extracellularly in the plasma fraction of the blood during active infection. This observation suggests that the interaction between FT and host plasma components may play an important role in survival and dissemination of the bacterium during the course of infection. Plasminogen (PLG) is a protein zymogen that is found in abundance in the blood of mammalian hosts. A number of both gram-positive and gram-negative bacterial pathogens have the ability to bind to PLG, giving them a survival advantage by increasing their ability to penetrate extracellular matrices and cross tissue barriers. RESULTS: We show that PLG binds to the surface of FT and that surface-bound PLG can be activated to plasmin in the presence of tissue PLG activator in vitro. In addition, using Far-Western blotting assays coupled with proteomic analyses of FT outer membrane preparations, we have identified several putative PLG-binding proteins of FT. CONCLUSIONS: The ability of FT to acquire surface bound PLG that can be activated on its surface may be an important virulence mechanism that results in an increase in initial infectivity, survival, and/or dissemination of this bacterium in vivo.

Immunization with heat-killed Francisella tularensis LVS elicits protective antibody-mediated immunity.

Francisella tularensis (FT) has been classified by the CDC as a category A pathogen because of its high virulence and the high mortality rate associated with infection via the aerosol route. Because there is no licensed vaccine available for FT, development of prophylactic and therapeutic regimens for the prevention/treatment of infection is a high priority. In this report, heat-killed FT live vaccine strain (HKLVS) was employed as a vaccine immunogen, either alone or in combination with an adjuvant, and was found to elicit protective immunity against high-dose FT live vaccine strain (FTLVS) challenge. FT-specific antibodies produced in response to immunization with HKLVS alone were subsequently found to completely protect naive mice against high-dose FT challenge in both infection-interference and passive immunization experiments. Additional passive immunization trials employing serum collected from mice immunized with a heat-killed preparation of an O-antigen-deficient transposon mutant of FTLVS (HKLVS-OAg(neg)) yielded similar results. These findings demonstrated that FT-specific antibodies alone can confer immunity against high-dose FTLVS challenge, and they reveal that antibody-mediated protection is not dependent upon production of LPS-specific antibodies.

A comparative study of four serological tumor markers for the detection of breast cancer.

Breast cancer is currently the third most common cause of cancer in the world. Circulating tumor antigens are often used as a minimally invasive tool for noting breast cancer progression. The objective of this study was to compare four tumor antigens (CA 15-3, CA 27.29, alpha-fetoprotein [AFP], and carcinoembryonic antigen [CEA]) for their diagnostic efficacy in breast cancer patients. It was hypothesized that CA 15-3 would proved to be superior to CA 27.29, CEA, and AFP in assay performance. Tumor marker assays were performed according to the manufacturers' directions. Assays used in this study were CA 15-3 and CA 27.29 (Fujirebio Diagnostics/Centocor Inc.), AFP (Abbott Inc.), and CEA (Hybritech Inc.). A total of 554 patient samples were obtained from an area hospital, plus 200 healthy adult samples which were used for the determination of normal reference intervals. The patients included patients with no disease (184), with non-malignant disease (11), with breast cancer (87), and with other types of cancer (272). Diagnostic percent sensitivities for each marker were: CA 15-3 (63%), CA 27.29 (39%), CEA (22%), and AFP (22%). Diagnostic specificities for each marker were comparable, ranging from 80-88%. Analytical parameters were evaluated for the assays and compared favorably. We concluded that CA 15-3 was the best tumor antigen for use as a diagnostic aid and monitoring agent.