Research

Superoxide dismutase A antigens derived from molecular analysis of sarcoidosis granulomas elicit systemic Th-1 immune responses

Shannon S Allen^{* 1} , Whitney Evans^{* 1} , James Carlisle¹ , Rana Hajizadeh¹ , Michele Nadaf¹ , Bryan E Shepherd² , David T Pride³ , Joyce E Johnson⁴ and Wonder P Drake^1,5

¹Department of Medicine, Division of Infectious Diseases, Vanderbilt University School of Medicine, Nashville, TN, USA

²Department of Biostatistics, Vanderbilt University School of Medicine, Nashville, TN, USA

³Department of Medicine, Division of Infectious Diseases, Stanford School of Medicine, Palo Alto, CA, USA

⁴Department of Pathology, Vanderbilt University School of Medicine, Nashville, TN, USA

⁵Department of Microbiology and Immunology, Vanderbilt University School of Medicine, Nashville, TN, USA

author email corresponding author email* Contributed equally

Respiratory Research 2008, 9:36doi:10.1186/1465-9921-9-36

Published:	25 April 2008

Abstract

Background

Sarcoidosis is an idiopathic granulomatous disease with pathologic and immunologic features similar to tuberculosis. Routine histologic staining and culture fail to identify infectious agents. An alternative means for investigating a role of infectious agents in human pathogenesis involves molecular analysis of pathologic tissues for microbial nucleic acids, as well as recognition of microbial antigens by the host immune system. Molecular analysis for superoxide dismutase A (sodA) allows speciation of mycobacteria. SodA is an abundantly secreted virulence factor that generates cellular immune responses in infected hosts. The purpose of this study is to investigate if target antigens of the sarcoidosis immune response can be identified by molecular analysis of sarcoidosis granulomas.

Methods

We detected sodA amplicons in 12 of 17 sarcoidosis specimens, compared to 2 of 16 controls (p = 0.001, two-tailed Fisher's exact test), and 3 of 3 tuberculosis specimens (p = 0.54). Analysis of the amplicons revealed sequences identical to M. tuberculosis (MTB) complex, as well as sequences which were genetically divergent. Using peripheral blood mononuclear cells (PBMC) from 12 of the 17 sarcoidosis subjects, we performed enzyme-linked immunospot assay (ELISPOT) to assess for immune recognition of MTB sodA peptides, along with PBMC from 26 PPD- healthy volunteers, and 11 latent tuberculosis subjects.

Results

Six of 12 sarcoidosis subjects recognized the sodA peptides, compared to one of 26 PPD- controls (p = 0.002), and 6/11 PPD+ subjects (p = .68). Overall, 10 of the 12 sarcoidosis subjects from whom we obtained PBMC and archival tissue possessed molecular or immunologic evidence for sodA.

Conclusion

Dual molecular and immunologic analysis increases the ability to find infectious antigens. The detection of Th-1 immune responses to sodA peptides derived from molecular analysis of sarcoidosis granulomas reveals that these are among the target antigens contributing to sarcoidosis granulomatous inflammation.