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NK Cell-Mediated Regulation of Protective Memory Responses against Intracellular Ehrlichial Pathogens.

Habib S, El Andaloussi A, Hisham A, Ismail N - PLoS ONE (2016)

Bottom Line: Ehrlichiae are gram-negative obligate intracellular bacteria that cause potentially fatal human monocytic ehrlichiosis.However, the contribution of NK cells to the memory response against Ehrlichia remains elusive.Together, these data suggest that E. muris-induced memory-like NK cells, which contribute to the protective, recall response against Ehrlichia.

View Article: PubMed Central - PubMed

Affiliation: Department of Obstetrics and Gynecology, Medical College of Georgia, Augusta University, Augusta, Georgia, United States of America.

ABSTRACT
Ehrlichiae are gram-negative obligate intracellular bacteria that cause potentially fatal human monocytic ehrlichiosis. We previously showed that natural killer (NK) cells play a critical role in host defense against Ehrlichia during primary infection. However, the contribution of NK cells to the memory response against Ehrlichia remains elusive. Primary infection of C57BL/6 mice with Ehrlichia muris provides long-term protection against a second challenge with the highly virulent Ixodes ovatus Ehrlichia (IOE), which ordinarily causes fatal disease in naïve mice. Here, we show that the depletion of NK cells in E. muris-primed mice abrogates the protective memory response against IOE. Approximately, 80% of NK cell-depleted E. muris-primed mice succumbed to lethal IOE infection on days 8-10 after IOE infection, similar to naïve mice infected with the same dose of IOE. The lack of a recall response in NK cell-depleted mice correlated with an increased bacterial burden, extensive liver injury, decreased frequency of Ehrlichia-specific IFN-γ-producing memory CD4+ and CD8+ T-cells, and a low titer of Ehrlichia-specific antibodies. Intraperitoneal infection of mice with E. muris resulted in the production of IL-15, IL-12, and IFN-γ as well as an expansion of activated NKG2D+ NK cells. The adoptive transfer of purified E. muris-primed hepatic and splenic NK cells into Rag2-/-Il2rg-/- recipient mice provided protective immunity against challenge with E. muris. Together, these data suggest that E. muris-induced memory-like NK cells, which contribute to the protective, recall response against Ehrlichia.

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NK cell depletion negatively affects antibody production and B cell expansion during memory response to Ehrlichia.Splenocytes were harvested from uninfected mice, IOE-infected mice, NK-/-EM/IOE-mice, and NK+/+EM/IOE mice on day 7 after IOE infection. Splenocytes from all groups were stimulated in vitro with IOE Ags. (A) Shows gating strategy on negative controls (naïve splenocytes that are not stimulated in vitro with Ags). Splenic mononuclear cells were gated based on forward and side scatter and then further analyzed for the expression of CD11c and B220. B220+CD11c+ and B220+ CD11c+cells were further analyzed for the expression of CD11b to define two cellular subsets; Plasmablasts (B220+CD11c+CD11b-) and B cells (B220+CD11c+ CD11b-). The percentages (B) and absolute numbers (C) of CD11b-CD11c+B220+ plasmablasts in NK-/-EM/IOE mice were significantly higher than the other groups of mice. The percentages (B) and absolute numbers (D) of CD11b-CD11c-B220+ B cells in NK-/-EM/IOE mice were significantly lower than the numbers of B cells in NK+/+EM/IOE but similar to those detected in unprimed mice infected with IOE. * and ** indicate P < 0.05 and P < 0.01, respectively. Data are presented as the means and SD of three mice per group and are representative of two independent experiments.
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pone.0153223.g011: NK cell depletion negatively affects antibody production and B cell expansion during memory response to Ehrlichia.Splenocytes were harvested from uninfected mice, IOE-infected mice, NK-/-EM/IOE-mice, and NK+/+EM/IOE mice on day 7 after IOE infection. Splenocytes from all groups were stimulated in vitro with IOE Ags. (A) Shows gating strategy on negative controls (naïve splenocytes that are not stimulated in vitro with Ags). Splenic mononuclear cells were gated based on forward and side scatter and then further analyzed for the expression of CD11c and B220. B220+CD11c+ and B220+ CD11c+cells were further analyzed for the expression of CD11b to define two cellular subsets; Plasmablasts (B220+CD11c+CD11b-) and B cells (B220+CD11c+ CD11b-). The percentages (B) and absolute numbers (C) of CD11b-CD11c+B220+ plasmablasts in NK-/-EM/IOE mice were significantly higher than the other groups of mice. The percentages (B) and absolute numbers (D) of CD11b-CD11c-B220+ B cells in NK-/-EM/IOE mice were significantly lower than the numbers of B cells in NK+/+EM/IOE but similar to those detected in unprimed mice infected with IOE. * and ** indicate P < 0.05 and P < 0.01, respectively. Data are presented as the means and SD of three mice per group and are representative of two independent experiments.

Mentions: Studies conducted by Winslow et al. have shown that chronic E. muris infection elicits a protective IgM response derived from extrafollicular CD11b-CD11c+B220+ plasmablasts. We found that primary or secondary IOE infection in naïve or E. muris–primed mice induced similar antigen-dependent expansion of CD11b-CD11c+B220+ plasmablasts in the spleen on day 7 after IOE infection when compared to in vitro Ag-stimulated splenocytes from naïve mice Fig 11A–11C. Interestingly, depletion of NK cells in NK-/- EM/IOE-infected mice significantly increased the frequency of these plasmablasts compared with NK+/+ EM/IOE-infected mice Fig 11A–11C. On the other hand, decreased antibody productions in NK-/- EM/IOE mice were associated with decreased percentage Fig 11A and 11B as well as absolute number Fig 11D of antigen-specific CD11b-CD11c-B220+ mature B cells. These data further suggest that chronic E. muris infection elicits NK cells that regulate antigen-specific T and B cell responses against Ehrlichia.


NK Cell-Mediated Regulation of Protective Memory Responses against Intracellular Ehrlichial Pathogens.

Habib S, El Andaloussi A, Hisham A, Ismail N - PLoS ONE (2016)

NK cell depletion negatively affects antibody production and B cell expansion during memory response to Ehrlichia.Splenocytes were harvested from uninfected mice, IOE-infected mice, NK-/-EM/IOE-mice, and NK+/+EM/IOE mice on day 7 after IOE infection. Splenocytes from all groups were stimulated in vitro with IOE Ags. (A) Shows gating strategy on negative controls (naïve splenocytes that are not stimulated in vitro with Ags). Splenic mononuclear cells were gated based on forward and side scatter and then further analyzed for the expression of CD11c and B220. B220+CD11c+ and B220+ CD11c+cells were further analyzed for the expression of CD11b to define two cellular subsets; Plasmablasts (B220+CD11c+CD11b-) and B cells (B220+CD11c+ CD11b-). The percentages (B) and absolute numbers (C) of CD11b-CD11c+B220+ plasmablasts in NK-/-EM/IOE mice were significantly higher than the other groups of mice. The percentages (B) and absolute numbers (D) of CD11b-CD11c-B220+ B cells in NK-/-EM/IOE mice were significantly lower than the numbers of B cells in NK+/+EM/IOE but similar to those detected in unprimed mice infected with IOE. * and ** indicate P < 0.05 and P < 0.01, respectively. Data are presented as the means and SD of three mice per group and are representative of two independent experiments.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4836677&req=5

pone.0153223.g011: NK cell depletion negatively affects antibody production and B cell expansion during memory response to Ehrlichia.Splenocytes were harvested from uninfected mice, IOE-infected mice, NK-/-EM/IOE-mice, and NK+/+EM/IOE mice on day 7 after IOE infection. Splenocytes from all groups were stimulated in vitro with IOE Ags. (A) Shows gating strategy on negative controls (naïve splenocytes that are not stimulated in vitro with Ags). Splenic mononuclear cells were gated based on forward and side scatter and then further analyzed for the expression of CD11c and B220. B220+CD11c+ and B220+ CD11c+cells were further analyzed for the expression of CD11b to define two cellular subsets; Plasmablasts (B220+CD11c+CD11b-) and B cells (B220+CD11c+ CD11b-). The percentages (B) and absolute numbers (C) of CD11b-CD11c+B220+ plasmablasts in NK-/-EM/IOE mice were significantly higher than the other groups of mice. The percentages (B) and absolute numbers (D) of CD11b-CD11c-B220+ B cells in NK-/-EM/IOE mice were significantly lower than the numbers of B cells in NK+/+EM/IOE but similar to those detected in unprimed mice infected with IOE. * and ** indicate P < 0.05 and P < 0.01, respectively. Data are presented as the means and SD of three mice per group and are representative of two independent experiments.
Mentions: Studies conducted by Winslow et al. have shown that chronic E. muris infection elicits a protective IgM response derived from extrafollicular CD11b-CD11c+B220+ plasmablasts. We found that primary or secondary IOE infection in naïve or E. muris–primed mice induced similar antigen-dependent expansion of CD11b-CD11c+B220+ plasmablasts in the spleen on day 7 after IOE infection when compared to in vitro Ag-stimulated splenocytes from naïve mice Fig 11A–11C. Interestingly, depletion of NK cells in NK-/- EM/IOE-infected mice significantly increased the frequency of these plasmablasts compared with NK+/+ EM/IOE-infected mice Fig 11A–11C. On the other hand, decreased antibody productions in NK-/- EM/IOE mice were associated with decreased percentage Fig 11A and 11B as well as absolute number Fig 11D of antigen-specific CD11b-CD11c-B220+ mature B cells. These data further suggest that chronic E. muris infection elicits NK cells that regulate antigen-specific T and B cell responses against Ehrlichia.

Bottom Line: Ehrlichiae are gram-negative obligate intracellular bacteria that cause potentially fatal human monocytic ehrlichiosis.However, the contribution of NK cells to the memory response against Ehrlichia remains elusive.Together, these data suggest that E. muris-induced memory-like NK cells, which contribute to the protective, recall response against Ehrlichia.

View Article: PubMed Central - PubMed

Affiliation: Department of Obstetrics and Gynecology, Medical College of Georgia, Augusta University, Augusta, Georgia, United States of America.

ABSTRACT
Ehrlichiae are gram-negative obligate intracellular bacteria that cause potentially fatal human monocytic ehrlichiosis. We previously showed that natural killer (NK) cells play a critical role in host defense against Ehrlichia during primary infection. However, the contribution of NK cells to the memory response against Ehrlichia remains elusive. Primary infection of C57BL/6 mice with Ehrlichia muris provides long-term protection against a second challenge with the highly virulent Ixodes ovatus Ehrlichia (IOE), which ordinarily causes fatal disease in naïve mice. Here, we show that the depletion of NK cells in E. muris-primed mice abrogates the protective memory response against IOE. Approximately, 80% of NK cell-depleted E. muris-primed mice succumbed to lethal IOE infection on days 8-10 after IOE infection, similar to naïve mice infected with the same dose of IOE. The lack of a recall response in NK cell-depleted mice correlated with an increased bacterial burden, extensive liver injury, decreased frequency of Ehrlichia-specific IFN-γ-producing memory CD4+ and CD8+ T-cells, and a low titer of Ehrlichia-specific antibodies. Intraperitoneal infection of mice with E. muris resulted in the production of IL-15, IL-12, and IFN-γ as well as an expansion of activated NKG2D+ NK cells. The adoptive transfer of purified E. muris-primed hepatic and splenic NK cells into Rag2-/-Il2rg-/- recipient mice provided protective immunity against challenge with E. muris. Together, these data suggest that E. muris-induced memory-like NK cells, which contribute to the protective, recall response against Ehrlichia.

Show MeSH
Related in: MedlinePlus