Susceptibility to SecondaryFrancisella tularensisLive Vaccine Strain Infection in B-Cell-Deficient Mice Is Associated with Neutrophilia but Not with Defects in Specific T-Cell-Mediated Immunity

Abstract

Previous studies have demonstrated a role for B cells, not associated with antibody production, in protection against lethal secondary infection of mice with Francisella tularensis live vaccine strain (LVS). However, the mechanism by which B cells contribute to this protection is not known. To study the specific role of B cells during secondary LVS infection, we developed an in vitro culture system that mimics many of the same characteristics of in vivo infection. Using this culture system, we showed that B cells do not directly control LVS infection but that control of LVS growth is mediated primarily by LVS-primed T cells. Importantly, B cells were not required for the generation of effective memory T cells since LVS-primed, B-cell-deficient (BKO) mice generated CD4؉ and CD8 ؉ T cells that controlled LVS infection similarly to LVS-primed CD4 ؉ and CD8 ؉ T cells from wild-type mice. The control of LVS growth appeared to depend primarily on gamma interferon and nitric oxide and was similar in wild-type and BKO mice. Rather, the inability of BKO mice to survive secondary LVS infection was associated with marked neutrophil influx into the spleen very early after challenge. The neutrophilia was directly associated with B cells, since BKO mice reconstituted with naive B cells prior to a secondary challenge with LVS had decreased bacterial loads and neutrophils in the spleen and survived.

Francisella tularensis LVS grown in macrophages has reduced ability to stimulate the secretion of inflammatory cytokines by macrophages in vitro

“…Secretion of inflammatory cytokines by macrophages is an important mechanism for controlling the proliferation of F. tularensis (3,5,22,25). Since F. tularensis that has grown in macrophages infects bystander cells, we compared F. tularensis grown in macrophages (FtMac) with bacteria grown in broth (FtB) for the ability to stimulate the secretion of inflammatory cytokines by macrophages.…”

“…Interleukin-12 (IL-12), which is primarily produced by macrophages, stimulates the secretion of IFN-γ by T cells. Infection of naive macrophages with F. tularensis stimulates low levels of IL-12 and TNF-α secretion, however, exposure to IFN-γ greatly increases the production of these cytokines and nitric oxide (5,22,25). Thus, the acute production of inflammatory cytokines such as TNF-α and IL-12 by macrophages may be important in controlling F. tularensis infections.…”

Direct and Indirect Impairment of Human Dendritic Cell Function by VirulentFrancisella tularensisSchu S4

“…Schu S4 was cultured in modified Mueller-Hinton broth ( [MMH] Mueller-Hinton broth supplemented with CaCl 2 , MgCl, 0.1% glucose, 0.025% ferric pyrophosphate and 2% Isovitalex) at 37°C with constant shaking overnight, aliquoted into 1-ml samples, frozen at Ϫ80°C, and thawed just prior to use, as previously described (7). Titers were determined in frozen stocks by enumerating viable bacteria from serial dilutions plated on MMH agar as previously described (9,19). The number of viable bacteria in frozen stock vials varied less than 5% over a 10-month period.…”

Genetic architecture of tuberculosis resistance in a mouse model of infection

“…B lymphocytes have been recently shown to play a role in resistance to intracellular pathogens that is distinct from their antibody-producing function. 23,27 Previously, the IgH b allotype has been associated with anergy and pulmonary granulomatous inflammation early after systemic injection of M. bovis BCG. 28,29 To start addressing B cell function in our model, we compared B lymphocytes in tuberculosis lung lesions in the parental B6 and C3H.B6-sst1 mice.…”