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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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Depletion of NK cells in NK-/-EM/IOE mice decreased production of IFN-γ.The levels of IFN-γ in bulk culture of splenocytes from the indicated mice groups, harvested on day 7 after IOE infection, and stimulated in vitro with either E. muris (A) or IOE (B) Ags, were measured by ELISA. The antigen-specific IFN-γ response was calculated by subtraction of the IFN-γ concentration produced by unstimulated cells from the Ags-stimulated cells. The data show a significantly lower production of E. muris- (A) and IOE- (B) specific IFN-γ by splenocytes from NK-/-EM/IOE mice compared with similarly-stimulated cells from NK+/+EM/IOE mice. The levels of IFN-γ in NK-/-EM/IOE-mice were similar to those detected in naïve mice infected with IOE. * and ** indicate P < 0.05 and P < 0.01, respectively. Data are representative of two independent experiments with four mice per group.
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pone.0153223.g009: Depletion of NK cells in NK-/-EM/IOE mice decreased production of IFN-γ.The levels of IFN-γ in bulk culture of splenocytes from the indicated mice groups, harvested on day 7 after IOE infection, and stimulated in vitro with either E. muris (A) or IOE (B) Ags, were measured by ELISA. The antigen-specific IFN-γ response was calculated by subtraction of the IFN-γ concentration produced by unstimulated cells from the Ags-stimulated cells. The data show a significantly lower production of E. muris- (A) and IOE- (B) specific IFN-γ by splenocytes from NK-/-EM/IOE mice compared with similarly-stimulated cells from NK+/+EM/IOE mice. The levels of IFN-γ in NK-/-EM/IOE-mice were similar to those detected in naïve mice infected with IOE. * and ** indicate P < 0.05 and P < 0.01, respectively. Data are representative of two independent experiments with four mice per group.

Mentions: To determine the difference in total IFN-y production in the spleen of NK cell-depleted and undepleted primed mice, we stimulated splenocytes from all mice groups with E. muris and IOE Ags, and measured IFN-γ levels in bulk culture supernatants by ELISA. Although in vitro stimulation of immune splenocytes with either E. muris or IOE Ags induced higher IFN-γ production as compared to that produced by naïve splenocytes, the levels of IFN-γ were lower when immune splenocytes were stimulated with IOE Ags. This is not surprising since our previous studies show that IOE is a poor inducer of IFN-γ response. Nevertheless, depletion of NK cells decreased the level of E. muris- Fig 9A or IOE- Fig 9B induced IFN-γ produced in the spleen of NK+/+EM/IOE-infected mice compared to that produced by splenocytes from NK-/-EM/IOE mice. Ag-specific IFN-γ production by the spleen of NK-/-EM/IOE mice was similar to that produced in the splenocytes cultured from unprimed, IOE-infected mice, suggesting that the absence of NK cells abrogated the protective memory response 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)

Depletion of NK cells in NK-/-EM/IOE mice decreased production of IFN-γ.The levels of IFN-γ in bulk culture of splenocytes from the indicated mice groups, harvested on day 7 after IOE infection, and stimulated in vitro with either E. muris (A) or IOE (B) Ags, were measured by ELISA. The antigen-specific IFN-γ response was calculated by subtraction of the IFN-γ concentration produced by unstimulated cells from the Ags-stimulated cells. The data show a significantly lower production of E. muris- (A) and IOE- (B) specific IFN-γ by splenocytes from NK-/-EM/IOE mice compared with similarly-stimulated cells from NK+/+EM/IOE mice. The levels of IFN-γ in NK-/-EM/IOE-mice were similar to those detected in naïve mice infected with IOE. * and ** indicate P < 0.05 and P < 0.01, respectively. Data are representative of two independent experiments with four mice per group.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0153223.g009: Depletion of NK cells in NK-/-EM/IOE mice decreased production of IFN-γ.The levels of IFN-γ in bulk culture of splenocytes from the indicated mice groups, harvested on day 7 after IOE infection, and stimulated in vitro with either E. muris (A) or IOE (B) Ags, were measured by ELISA. The antigen-specific IFN-γ response was calculated by subtraction of the IFN-γ concentration produced by unstimulated cells from the Ags-stimulated cells. The data show a significantly lower production of E. muris- (A) and IOE- (B) specific IFN-γ by splenocytes from NK-/-EM/IOE mice compared with similarly-stimulated cells from NK+/+EM/IOE mice. The levels of IFN-γ in NK-/-EM/IOE-mice were similar to those detected in naïve mice infected with IOE. * and ** indicate P < 0.05 and P < 0.01, respectively. Data are representative of two independent experiments with four mice per group.
Mentions: To determine the difference in total IFN-y production in the spleen of NK cell-depleted and undepleted primed mice, we stimulated splenocytes from all mice groups with E. muris and IOE Ags, and measured IFN-γ levels in bulk culture supernatants by ELISA. Although in vitro stimulation of immune splenocytes with either E. muris or IOE Ags induced higher IFN-γ production as compared to that produced by naïve splenocytes, the levels of IFN-γ were lower when immune splenocytes were stimulated with IOE Ags. This is not surprising since our previous studies show that IOE is a poor inducer of IFN-γ response. Nevertheless, depletion of NK cells decreased the level of E. muris- Fig 9A or IOE- Fig 9B induced IFN-γ produced in the spleen of NK+/+EM/IOE-infected mice compared to that produced by splenocytes from NK-/-EM/IOE mice. Ag-specific IFN-γ production by the spleen of NK-/-EM/IOE mice was similar to that produced in the splenocytes cultured from unprimed, IOE-infected mice, suggesting that the absence of NK cells abrogated the protective memory response 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