Scientific Publications by FDA Staff

Infect Immun 2008 Sep;76(9):4311-21

Diverse myeloid and lymphoid cell subpopulations produce gamma interferon during early innate immune responses to Francisella tularensis live vaccine strain.

De Pascalis R, Taylor BC, Elkins KL

De Pascalis, R, US FDA, Ctr Biol Res & Evaluat, Lab Mycobacterial Dis & Cellular Immunol, 1401 Rockville Pike,HFM 431, Rockville, MD 20852 USA. US FDA, Ctr Biol Res & Evaluat, Lab Mycobacterial Dis & Cellular Immunol, Rockville, MD 20852 USA Univ Penn, Dept Pathol, Philadelphia, PA 19104 USA

Francisella tularensis, a small gram-negative intracellular bacterium responsible for causing tularemia, is highly pathogenic and classified as a Category A agent of bioterrorism. As for other intracellular pathogens, successful protective immune responses to Francisella tularensis require rapid and efficient induction of interferon gamma (IFN-gamma) production. Studies using intracellular bacteria such as Listeria monocytogenes as well as Francisella suggest that natural killer (NK) and T cells are important sources of IFN-gamma. However, comprehensive characterization of specific sources of IFN-gamma produced during Francisella infection in vivo remains incomplete, and depletion of NK cells before infection of mice with F. tularensis Live Vaccine Strain (LVS) has little impact on the course or outcome of infection. Here, we determined the cell subpopulations that respond quickly to intradermal F. tularensis Live Vaccine Strain (LVS) infection of mice by producing IFN-gamma within hours to a few days. Splenic and liver lymphocytes were obtained from LVS-infected mice, and analyzed using RT-PCR of IFN-gamma mRNA, intracellular cytokine expression using multiparameter flow cytometry, and ex vivo production of IFN-gamma protein by ELISA. Cells producing IFN-gamma were readily detectable by day 3 after infection, and numbers progressively increased through days 5 - 7. Importantly, the cell types responsible for IFN-gamma production were much more varied than expected: these included not only NK cells and T cells, which might be predicted, but also other cells including dendritic cells, "NK DCs," NK T cells, and neutrophils. Most importantly, since RAG-1 knockout mice appeared to exhibit a frequency of IFN-gamma-producing cells comparable to that of intact wild type mice, early IFN-gamma production by innate immune cells does not depend on the presence of T or B cells.