Detection of M. tuberculosis DNA in sarcoidosis: correlation with T-cell response

The pathogenetic role of Mycobacterium tuberculosis (M. tuberculosis) in tuberculosis is well defined, whereas its role in sarcoidosis is controversial. In sarcoidosis, activation of T-helper cells is observed, which is comparable to tuberculosis. The aim of this study was first to investigate whether M. tuberculosis DNA could be retrospectively detected in samples of patients with clinically verified sarcoidosis by polymerase chain reaction (PCR) and second, to analyze the relationship between M. tuberculosis DNA positive samples and T-cell response in sarcoidosis patients. Formalin fixed paraffin-embedded lung tissues or cell sediments of bronchoalveolar lavage, respectively, from 65 patients with sarcoidosis and lung tissues from 40 tuberculosis patients were investigated by means of different PCR assays in comparison to control samples. The primers used were derived from insertion sequence IS 986/6110 specific for the M. tuberculosis complex (123 bp PCR) and from the gene encoding the 38 kDa protein antigen b (419 bp PCR). The 123 bp assay yielded a specificity of 97% and a sensitivity of 95%. In contrast, the 419 bp PCR method showed a lower sensitivity of only 8% likely because of possible DNA degradation during fixation and embedding procedures of the tissue and the fact that this PCR uses a single copy element as target. We amplified the M. tuberculosis complex specific 123 bp fragment in 64% of samples from sarcoidosis patients. The specificity of PCR products in these cases was confirmed by DNA sequencing. Interestingly in the M. tuberculosis positive sarcoidoses, we found increased serum levels of soluble interleukin-2 receptor in correlation to the sarcoidosis stages (p < 0.05). In conclusion, the determination of M. tuberculosis by PCR alone does not permit a differentiation between sarcoidosis and tuberculosis. However these results support the contention that M. tuberculosis may play a pathogenetic role at least in the part of sarcoidosis patients with elevated interleukin-2 receptor values.