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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 in EM/IOE-infected mice impairs expansion of effector memory CD4+ T cells.Splenocytes harvested on day 7 after IOE infection from NK-/-EM/IOE and NK+/+EM/IOE-mice were stimulated in vitro with IOE antigens and the frequency of antigen-specific activated/effector memory T cells were determined by flow cytometry. Naïve cells were stimulated in vitro with IOE antigens. Gating on splenocytes and T cells was shown in (A). The spleens of NK-/-EM/IOE-mice contained lower percentages (B) and absolute numbers (C) of CD62L+CD4+ T cells compared to that detected in the spleens of NK+/+EM/IOE-infected mice on day 7 post-IOE infection. Data are presented as the means ± SD of four mice per group from two independent experiments. ** indicates P < 0.01.
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pone.0153223.g005: NK cell depletion in EM/IOE-infected mice impairs expansion of effector memory CD4+ T cells.Splenocytes harvested on day 7 after IOE infection from NK-/-EM/IOE and NK+/+EM/IOE-mice were stimulated in vitro with IOE antigens and the frequency of antigen-specific activated/effector memory T cells were determined by flow cytometry. Naïve cells were stimulated in vitro with IOE antigens. Gating on splenocytes and T cells was shown in (A). The spleens of NK-/-EM/IOE-mice contained lower percentages (B) and absolute numbers (C) of CD62L+CD4+ T cells compared to that detected in the spleens of NK+/+EM/IOE-infected mice on day 7 post-IOE infection. Data are presented as the means ± SD of four mice per group from two independent experiments. ** indicates P < 0.01.

Mentions: To determine the effect of NK cell depletion on the frequency of activated/effector memory CD4+ T cells following secondary IOE infection, we measured the expression of CD62L and CD44 on T cells in the spleen of NK-/-EM/IOE and NK+/+EM/IOE mice 7 DPI after IOE infection. Following in vitro stimulation with IOE antigens, we detected lower a percentage and absolute number of activated CD62L+ and effector/effector memory CD44+CD4+T cells in the spleen of NK-/-EM/IOE mice than that detected in the spleen of NK+/+EM/IOE mice Fig 5A–5C. NK cell depletion also significantly decreased the percentage and absolute number Fig 6A–6C of effector/effector memory CD44+CD8+ T cells, but not CD62L+CD8+ T cells, in NK-/-EM/IOE mice when compared to NK+/+EM/IOE mice. In vitro stimulation of naïve splenocytes with IOE or E. muris (data not shown) did not elicit significant activation of CD4+ T cells or naïve CD8+ T cells as compared to primed mice. Together, these data suggest that NK cells promote expansion of effector/effector memory CD4+ T cells and CD8+ T cells following primary and secondary Ehrlichia infection.


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 in EM/IOE-infected mice impairs expansion of effector memory CD4+ T cells.Splenocytes harvested on day 7 after IOE infection from NK-/-EM/IOE and NK+/+EM/IOE-mice were stimulated in vitro with IOE antigens and the frequency of antigen-specific activated/effector memory T cells were determined by flow cytometry. Naïve cells were stimulated in vitro with IOE antigens. Gating on splenocytes and T cells was shown in (A). The spleens of NK-/-EM/IOE-mice contained lower percentages (B) and absolute numbers (C) of CD62L+CD4+ T cells compared to that detected in the spleens of NK+/+EM/IOE-infected mice on day 7 post-IOE infection. Data are presented as the means ± SD of four mice per group from two independent experiments. ** indicates P < 0.01.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0153223.g005: NK cell depletion in EM/IOE-infected mice impairs expansion of effector memory CD4+ T cells.Splenocytes harvested on day 7 after IOE infection from NK-/-EM/IOE and NK+/+EM/IOE-mice were stimulated in vitro with IOE antigens and the frequency of antigen-specific activated/effector memory T cells were determined by flow cytometry. Naïve cells were stimulated in vitro with IOE antigens. Gating on splenocytes and T cells was shown in (A). The spleens of NK-/-EM/IOE-mice contained lower percentages (B) and absolute numbers (C) of CD62L+CD4+ T cells compared to that detected in the spleens of NK+/+EM/IOE-infected mice on day 7 post-IOE infection. Data are presented as the means ± SD of four mice per group from two independent experiments. ** indicates P < 0.01.
Mentions: To determine the effect of NK cell depletion on the frequency of activated/effector memory CD4+ T cells following secondary IOE infection, we measured the expression of CD62L and CD44 on T cells in the spleen of NK-/-EM/IOE and NK+/+EM/IOE mice 7 DPI after IOE infection. Following in vitro stimulation with IOE antigens, we detected lower a percentage and absolute number of activated CD62L+ and effector/effector memory CD44+CD4+T cells in the spleen of NK-/-EM/IOE mice than that detected in the spleen of NK+/+EM/IOE mice Fig 5A–5C. NK cell depletion also significantly decreased the percentage and absolute number Fig 6A–6C of effector/effector memory CD44+CD8+ T cells, but not CD62L+CD8+ T cells, in NK-/-EM/IOE mice when compared to NK+/+EM/IOE mice. In vitro stimulation of naïve splenocytes with IOE or E. muris (data not shown) did not elicit significant activation of CD4+ T cells or naïve CD8+ T cells as compared to primed mice. Together, these data suggest that NK cells promote expansion of effector/effector memory CD4+ T cells and CD8+ T cells following primary and secondary Ehrlichia infection.

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