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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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E. muris induces an optimal cytokine environment that promotes induction and maintenance of memory-like NK cells.Cultured supernatants of liver mononuclear cells (LMNCs) harvested 3, 5, 7 and 14 DPI from E. muris-primed mice and stimulated in vitro with E. muris Ag contained significantly higher levels of IL-12 (A), IL-15 (B) and IFN-γ (C) compared to LMNCs from naïve mice and IOE-primed mice. On the other hand, LMNC culture supernatant from IOE-primed mice contained higher levels of IL-10 as compared to naïve mice and E. muris-primed mice (D). *, ** indicate P < 0.05 and P < 0.01, respectively. Data are presented as the means ± SD of 3 mice/ group and are representative of two independent experiments.
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pone.0153223.g013: E. muris induces an optimal cytokine environment that promotes induction and maintenance of memory-like NK cells.Cultured supernatants of liver mononuclear cells (LMNCs) harvested 3, 5, 7 and 14 DPI from E. muris-primed mice and stimulated in vitro with E. muris Ag contained significantly higher levels of IL-12 (A), IL-15 (B) and IFN-γ (C) compared to LMNCs from naïve mice and IOE-primed mice. On the other hand, LMNC culture supernatant from IOE-primed mice contained higher levels of IL-10 as compared to naïve mice and E. muris-primed mice (D). *, ** indicate P < 0.05 and P < 0.01, respectively. Data are presented as the means ± SD of 3 mice/ group and are representative of two independent experiments.

Mentions: Recent studies have suggested that NK cells previously activated by cytokines or by ligation of their activating NK receptors (including FcR) display memory-like phenotypes, which cause them to respond more robustly to reactivation [29]. Because primary infection with a low dose of IOE does not confer a protective memory response, we hypothesized that E. muris infection may differentially activate innate immune cells and induce a different cytokine environment that promotes the differentiation of NK cells into a memory phenotype. Thus, we examined the levels of cytokines that are known to promote the survival, proliferation, IFN-γ production and cytotoxicity of NK cells, namely IL-12, IL-15, and IL-18, in the liver of infected mice. We also measured the level of IL-10 in these mice, which is known to impair protective primary and memory immune responses against Ehrlichia [26,30]. LMNCs from E. muris-infected mice were harvested 3, 5, 7 and 14 DPI and cells were stimulated with E. muris Ags. Compared with IOE-infected mice, LMNCs from E. muris-infected mice secreted higher levels of IL-12 and IFN-γ at 7 and 14 DPI and a higher level of IL-15 at 14 DPI. Fig 13A–13C. In contrast, we detected higher production of IL-10 by LMNCs from IOE-infected mice at 7 and 14 DPI as compared with E. muris-infected mice Fig 13D.


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

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

E. muris induces an optimal cytokine environment that promotes induction and maintenance of memory-like NK cells.Cultured supernatants of liver mononuclear cells (LMNCs) harvested 3, 5, 7 and 14 DPI from E. muris-primed mice and stimulated in vitro with E. muris Ag contained significantly higher levels of IL-12 (A), IL-15 (B) and IFN-γ (C) compared to LMNCs from naïve mice and IOE-primed mice. On the other hand, LMNC culture supernatant from IOE-primed mice contained higher levels of IL-10 as compared to naïve mice and E. muris-primed mice (D). *, ** indicate P < 0.05 and P < 0.01, respectively. Data are presented as the means ± SD of 3 mice/ group and are representative of two independent experiments.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0153223.g013: E. muris induces an optimal cytokine environment that promotes induction and maintenance of memory-like NK cells.Cultured supernatants of liver mononuclear cells (LMNCs) harvested 3, 5, 7 and 14 DPI from E. muris-primed mice and stimulated in vitro with E. muris Ag contained significantly higher levels of IL-12 (A), IL-15 (B) and IFN-γ (C) compared to LMNCs from naïve mice and IOE-primed mice. On the other hand, LMNC culture supernatant from IOE-primed mice contained higher levels of IL-10 as compared to naïve mice and E. muris-primed mice (D). *, ** indicate P < 0.05 and P < 0.01, respectively. Data are presented as the means ± SD of 3 mice/ group and are representative of two independent experiments.
Mentions: Recent studies have suggested that NK cells previously activated by cytokines or by ligation of their activating NK receptors (including FcR) display memory-like phenotypes, which cause them to respond more robustly to reactivation [29]. Because primary infection with a low dose of IOE does not confer a protective memory response, we hypothesized that E. muris infection may differentially activate innate immune cells and induce a different cytokine environment that promotes the differentiation of NK cells into a memory phenotype. Thus, we examined the levels of cytokines that are known to promote the survival, proliferation, IFN-γ production and cytotoxicity of NK cells, namely IL-12, IL-15, and IL-18, in the liver of infected mice. We also measured the level of IL-10 in these mice, which is known to impair protective primary and memory immune responses against Ehrlichia [26,30]. LMNCs from E. muris-infected mice were harvested 3, 5, 7 and 14 DPI and cells were stimulated with E. muris Ags. Compared with IOE-infected mice, LMNCs from E. muris-infected mice secreted higher levels of IL-12 and IFN-γ at 7 and 14 DPI and a higher level of IL-15 at 14 DPI. Fig 13A–13C. In contrast, we detected higher production of IL-10 by LMNCs from IOE-infected mice at 7 and 14 DPI as compared with E. muris-infected mice Fig 13D.

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