Abstract
Our results do not suggest a link between mycobacteria and pulmonary MALT lymphoma: high-speed sequencing is needed http://ow.ly/xXXm301AQ6r
To the Editor:
We read with great interest the review of Borie et al. [1] on pulmonary lymphoma of the mucosa-associated lymphoid tissue (MALT). We agree with the hypothesis that chronic antigen stimulation of microbial origin may lead to the development of pulmonary MALT lymphoma. Indeed, MALT lymphoma has been associated with various chronic infections in extrapulmonary localisations. This link has previously been demonstrated between Helicobacter pylori infection and gastric MALT lymphoma, and suggested with Campylobacter jejuni, Chlamydia psittaci and Borrelia burgdorferi with small intestine lymphoma, ocular annexa lymphoma and cutaneous lymphoma, respectively. Similarly a link has recently been suggested between infection with Achromobacter xylosoxidans and pulmonary MALT lymphoma [2].
Only a minority of pathogens have the ability to persist in the lung for a long period of time. Our group has investigated a link between pulmonary MALT lymphoma and mycobacterial infection for three reasons. Persistence of M. avium complex has been observed in diverse organs without clinical disease in HIV infection as in animal models [3, 4]. M. tuberculosis DNA has been found by in situ PCR within the normal lung of individuals that have died from causes other than tuberculosis [5, 6]. A previously reported case suggested a temporal link between the occurrence of MALT lymphoma and mycobacterial pulmonary infection, and an improvement of a pulmonary MALT lymphoma after an anti-tuberculous therapy regimen for concomitant pulmonary tuberculosis [7]. In addition, two patients with pulmonary MALT lymphoma have been successfully treated with prolonged clarithromycin therapy [8].
We performed conventional PCR on DNA extracted from frozen or paraffin-embedded lung tissue obtained by surgical biopsies in eight cases of primary MALT pulmonary lymphoma and two controls with lung cancer (involving the lesion in MALT cases and normal parenchyma in controls). We used two couples of primers: one targeting the IS6110 gene of M. tuberculosis and one targeting the hsp65 gene of mycobacteria genera. We also carried out a universal bacterial PCR amplifying the gene encoding for ribosomal 16S RNA.
No mycobacterial DNA was detected. 16S rDNA PCR was positive in one patient and one control. The sequence of the amplified products gave a mix of bacteria. These PCR products were then cloned and sequenced (six clones/PCR products). The results of the sequences showed the identification of environmental species (five clones in lymphoma patients and four clones in the control cases) and Propionibacterium acnes (one clone in the patients and two clones in the control cases).
Hence, our results do not suggest a link between chronic mycobacterial infection and the occurrence of pulmonary MALT lymphoma. However, bacteria may be difficult to identify in tissue by PCR because of the small amount of microbial DNA in the samples used. Sensitivity varies according to the target gene and the modality of PCR [9]. More recently, new generations of PCR have been developed. High-throughput sequencing allows the detection of any pathogen, bacterial, fungal or viral, in frozen tissue without the necessity for a defined target sequence [10]. We agree with Borie et al. [1] that a non-targeted approach now has to be performed in order to detect whether pulmonary MALT lymphoma is associated with specific pathogens.
Footnotes
Conflict of interest: None declared.
- Received May 5, 2016.
- Accepted June 4, 2016.
- Copyright ©ERS 2016