Abstract
BackgroundTo initiate infection, Bacillus anthracis needs to overcome the host innate immune system. Anthrax toxin, a major virulence factor of B. anthracis, impairs both the innate and adaptive immune systems and is important in the establishment of anthrax infections.Methodology/Principal FindingsTo measure the ability of anthrax toxin to target immune cells, studies were performed using a fusion of the anthrax toxin lethal factor (LF) N-terminal domain (LFn, aa 1–254) with β-lactamase (LFnBLA). This protein reports on the ability of the anthrax toxin protective antigen (PA) to mediate LF delivery into cells. Primary immune cells prepared from mouse spleens were used in conjunction with flow cytometry to assess cleavage and resulting FRET disruption of a fluorescent β-lactamase substrate, CCF2/AM. In spleen cell suspensions, the macrophages, dendritic cells, and B cells showed about 75% FRET disruption of CCF2/AM due to cleavage by the PA–delivered LFnBLA. LFnBLA delivery into CD4+ and CD8+ T cells was lower, with 40% FRET disruption. When the analyses were done on purified samples of individual cell types, similar results were obtained, with T cells again having lower LFnBLA delivery than macrophages, dendritic cells, and B cells. Relative expression levels of the toxin receptors CMG2 and TEM8 on these cells were determined by real-time PCR. Expression of CMG2 was about 1.5-fold higher in CD8+ cells than in CD4+ and B cells, and 2.5-fold higher than in macrophages.Conclusions/SignificanceAnthrax toxin entry and activity differs among immune cells. Macrophages, dendritic cells, and B cells displayed higher LFnBLA activity than CD4+ and CD8+ T cells in both spleen cell suspension and the purified samples of individual cell types. Expression of anthrax toxin receptor CMG2 is higher in CD4+ and CD8+ T cells, which is not correlated to the intracellular LFnBLA activity.
Highlights
Bacillus anthracis is a gram-positive, spore forming bacterial pathogen
We found that 54.6+/2 10.0% of spleen cells underwent fluorescence resonance energy transfer (FRET) disruption after 1 h of LFnBLA + protective antigen (PA) treatment, compared to the untreated control cells or those treated with LFnBLA alone (Figure 2B–2D)
It is important to determine the relative activities of the toxins in various immune cell types in order to better understand the interaction of this pathogen and the immune system
Summary
Anthrax infection occurs when dormant spores enter an animal and germinate, resulting in growth and dissemination of vegetative bacteria. Anthrax infections can occur in three forms, inhalational, gastrointestinal, and cutaneous, depending on the route by which spores enter the host [1]. Histopathological studies showed that in inhalational anthrax, spores in the lungs are efficiently taken up by phagocytic cells and transported to the regional lymph nodes [2]. Some studies suggested that macrophages act as Trojan horses, allowing spores to germinate and grow into vegetative cells [3,4]. Mice depleted of macrophages are more susceptible to anthrax infection [8], supporting a protective role for these cells. Bacillus anthracis needs to overcome the host innate immune system. A major virulence factor of B. anthracis, impairs both the innate and adaptive immune systems and is important in the establishment of anthrax infections
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
