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Microbiology (Reading, England)2010; 156(Pt 6); 1836-1847; doi: 10.1099/mic.0.035915-0

Identification of Rhodococcus equi lipids recognized by host cytotoxic T lymphocytes.

Abstract: Immune adult horses have CD8(+) cytotoxic T lymphocytes (CTLs) that recognize and lyse Rhodococcus equi-infected cells in an equine lymphocyte alloantigen (ELA)-A [classical major histocompatibility complex (MHC) class I]-unrestricted fashion. As protein antigens are MHC class I-restricted, the lack of restriction suggests that the bacterial antigens being recognized by the host are not proteins. The goals of this study were to test the hypothesis that these CTLs recognize unique R. equi cell-wall lipids related to mycobacterial lipids. Initial experiments showed that treatment of soluble R. equi antigen with broadly reactive proteases did not significantly diminish the ability of the antigen to stimulate R. equi-specific CTLs. R. equi-specific CTLs were also shown to lyse target cells (equine macrophages) pulsed with an R. equi lipid extract. Analysis of the R. equi lipid by TLC and MS (MALDI-TOF and ES) indicated that the extracted antigen consisted of three primary fractions: trehalose monomycolate (TMM), trehalose dimycolate (TDM) and cardiolipin (CL). ELA-A-mismatched cells pulsed with purified TMM and CL, but not the TDM fraction, were recognized and lysed by R. equi-specific CTLs. Because of their role in immune clearance and pathogenesis, transcription of the cytokines gamma interferon (IFN-gamma) and interleukin-4 (IL-4) was also measured in response to R. equi lipids by using real-time PCR; elevated IFN-gamma, but not IL-4, was associated with host clearance of the bacteria. The whole-cell R. equi lipid and all three R. equi lipid fractions resulted in marked increases in IFN-gamma transcription, but no increase in IL-4 transcription. Together, these data support the hypothesis that immune recognition of unique lipids in the bacterial cell wall is an important component of the protective immune response to R. equi. The results also identify potential lipid antigens not previously shown to be recognized by CTLs in an important, naturally occurring actinomycete bacterial pathogen.
Publication Date: 2010-03-18 PubMed ID: 20299405PubMed Central: PMC4086205DOI: 10.1099/mic.0.035915-0Google Scholar: Lookup
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  • Journal Article
  • Research Support
  • Non-U.S. Gov't

Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

The researchers investigated the immune response of adult horses to Rhodococcus equi, a type of bacteria, with a focus on identifying the bacterial lipids that cytotoxic T lymphocytes (immune system cells) recognize. Results showed the immune system recognition of unique lipids present within the bacterial cell wall, particularly trehalose monomycolate and cardiolipin, plays a key role in effective immune responses.

Research Objectives and Hypothesis

  • The primary aim of the research was to establish whether cytotoxic T lymphocytes recognize unique cell-wall lipids in Rhodococcus equi, which relate to mycobacterial lipids, based on the fact that the immune response was not restricted in the way it typically is for protein antigens.

Methodology

  • Initial experiments involved treating soluble R. equi antigens with proteases to see if the immune response would weaken. This was not the case, which suggested that proteins were not the antigens triggering the response.
  • Researchers extracted the lipid from R. equi and exposed it to T lymphocytes, and revealed that the lymphocytes were able to destroy target cells (macrophages) pulsed with the lipid.
  • The team used thin-layer chromatography and mass spectroscopy to further analyze the lipid, finding it contained mainly trehalose monomycolate (TMM), trehalose dimycolate (TDM) and cardiolipin (CL).
  • Cells exposed to TMM and CL were recognized and destroyed by the T lymphocytes, but those exposed to TDM were not.
  • The researchers also measured cytokine (a type of immune response protein) transcription in response to the R. equi lipids. The study showed increased transcription of interferon-gamma but not interleukin-4, the former being associated with bacterial clearance.

Findings and Conclusion

  • The results pointed to the immune system’s recognition of these unique bacterial cell wall lipids as a significant part of the protective response against R. equi.
  • The findings also identified potential lipid antigens that have not previously been recognized as key elements in the immune response to this bacterial pathogen. The two isolated lipid fractions, TMM and CL, were shown to trigger the response of cytotoxic T lymphocytes without any restriction, leading to the destruction of infected cells.

These results help broaden the overall understanding of how the immune systems of horses (and potentially other organisms) combat bacterial infections on the cellular level. This could lead to improved treatment strategies for diseases caused by similar bacteria.

Cite This Article

APA
Harris SP, Fujiwara N, Mealey RH, Alperin DC, Naka T, Goda R, Hines SA. (2010). Identification of Rhodococcus equi lipids recognized by host cytotoxic T lymphocytes. Microbiology (Reading), 156(Pt 6), 1836-1847. https://doi.org/10.1099/mic.0.035915-0

Publication

ISSN: 1465-2080
NlmUniqueID: 9430468
Country: England
Language: English
Volume: 156
Issue: Pt 6
Pages: 1836-1847

Researcher Affiliations

Harris, Seth P
  • Department of Veterinary Microbiology and Pathology, Washington State University, College of Veterinary Medicine, PO Box 647040, Pullman, WA 99164-7040, USA.
Fujiwara, Nagatoshi
  • Department of Bacteriology, Osaka City University, Graduate School of Medicine, 1-4-3 Asahi-machi, Abeno-Ku, Osaka 545-8585, Japan.
Mealey, Robert H
  • Department of Veterinary Microbiology and Pathology, Washington State University, College of Veterinary Medicine, PO Box 647040, Pullman, WA 99164-7040, USA.
Alperin, Debra C
  • Department of Veterinary Microbiology and Pathology, Washington State University, College of Veterinary Medicine, PO Box 647040, Pullman, WA 99164-7040, USA.
Naka, Takashi
  • Department of Bacteriology, Osaka City University, Graduate School of Medicine, 1-4-3 Asahi-machi, Abeno-Ku, Osaka 545-8585, Japan.
Goda, Reina
  • Department of Bacteriology, Osaka City University, Graduate School of Medicine, 1-4-3 Asahi-machi, Abeno-Ku, Osaka 545-8585, Japan.
Hines, Stephen A
  • Department of Veterinary Microbiology and Pathology, Washington State University, College of Veterinary Medicine, PO Box 647040, Pullman, WA 99164-7040, USA.

MeSH Terms

  • Animals
  • Antigens, Bacterial / immunology
  • Cell Wall / immunology
  • Horses / immunology
  • Horses / microbiology
  • Interferon-gamma / immunology
  • Interleukin-4 / genetics
  • Interleukin-4 / immunology
  • Leukocytes, Mononuclear / immunology
  • Lipids / immunology
  • Rhodococcus equi / cytology
  • Rhodococcus equi / immunology
  • T-Lymphocytes, Cytotoxic / immunology

Grant Funding

  • T32 AI007025 / NIAID NIH HHS
  • T32 AI007025-24 / NIAID NIH HHS

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Citations

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