Pulmonary Mycobacterium celatum immune restoration disease: immunopathology and response to corticosteroid therapy

Antiretroviral therapy (ART) in immunodeficient HIV patients may be complicated by mycobacterial immune restoration disease (IRD) resulting from an immunopathological response to subclinical infections by non-tuberculous mycobacteria (NTM) [1]. The most common presentation is lymphadenitis associated with Mycobacterium avium complex infection. Pathogenic mechanisms in mycobacterial IRD are incompletely understood, but data accumulated thus far suggest that delayed-type hypersensitivity (DTH) responses to mycobacterial antigens are a cause of tissue inflammation [1–3]. We report a case of Mycobacterium celatum IRD, presenting with pneumonitis, and present data illustrating the immunopathological nature of this disease. A 48-year-old man with past Pneumocystis jiroveci pneumonia and disseminated cytomegalovirus infection was commenced on lopinavir/ritonavir, zidovudine and lamivudine when the CD4 T-cell count was 48 cells/μl (6%) and the plasma HIV-1-RNA level was greater than 100 000 copies/ml. He was receiving prophylactic azithromycin and maintenance valganciclovir. On day 11 of ART he developed fever, and chest radiography (previously normal) showed patchy consolidation in both lungs. A computed tomography (CT) scan of the thorax demonstrated an area of consolidation in the left upper lobe and scattered nodular opacities in the left lower lobe and right lung (Fig. 1a). Sputum collected on days 12, 13 and 14 of ART yielded M. celatum from both mycobacteria growth indicator tube media and Löwenstein–Jensen agar, confirmed by 16S ribosomal RNA gene sequencing. However, repeated culture of blood using the BACTEC 460 system did not demonstrate mycobacteremia.Fig. 1: High resolution computed tomography scan of the thorax at presentation with Mycobacterium celatum immune restoration disease (a) and 24 weeks after commencing prednisone (b). At presentation the scan demonstrates an area of consolidation in the left lung and a nodule in the right lung consistent with granulomatous inflammation. Residual cystic changes from previous Pneumocystis jiroveci pneumonia are also present.On day 27, the plasma HIV-1-RNA level had decreased to 933 copies/ml and the CD4 T-cell count had increased to 144 cells/μl (24%). DTH skin testing demonstrated an 18 mm response to tuberculin and a 10 mm response to Mycobacterium avium purified protein derivative (PPD) using antigens from the Commonwealth Serum Laboratories (Melbourne, Australia). Skin testing had not been performed before commencing ART, but anergy was likely given the severity of his immunodeficiency [4]. A punch skin biopsy was taken from the tuberculin skin test site and immunohistological examination, using murine monoclonal antibodies to CD3, CD4 and CD8 (Nova Castra, Newcastle-upon-Tyne, UK), demonstrated a lymphocytic infiltrate, which consisted predominantly of T cells with a CD4/CD8 T-cell ratio of 8: 1. Whole blood samples were tested for mycobacteria-specific T cells using IFN-γ release assays (QuantiFERON-TB or QuantiFERON-TB Gold; Cellestis, Carnegie, Victoria, Australia) according to the manufacturer's instructions [5,6]. Specific activities of 64% (reference < 15%) and 46% (reference < 20%) were obtained with tuberculin and M. avium PPD, respectively, using the QuantiFERON-TB assay, but there was no response to the ESAT-6 or CFP-10 antigens of tuberculin using the QuantiFERON-TB Gold assay. These findings suggest the presence of T cells reacting with antigens of NTM. Five years previously, when his CD4 T-cell count was 1218 cells/μl, the QuantiFERON-TB assay did not show specific activity to either tuberculin or M. avium PPD. Pentoxifylline, a tumour necrosis factor inhibitor, was commenced in an attempt to suppress inflammation, but was ceased after 4 weeks because it was ineffective. Anaemia and leukopenia had been present since starting ART and were not improved by the cessation of valganciclovir or the substitution of tenofovir for zidovudine. The serum C-reactive protein level, which had declined after treatment of P. jiroveci pneumonia and cytomegalovirus infection, rose after the commencement of ART. Prednisone 10 mg a day was initiated and was associated with a resolution of the cytopenias and normalization of serum C-reactive protein levels. The patient's symptoms resolved completely and a CT scan undertaken 24 weeks after commencing prednisone showed significant improvement (Fig. 1b). This is the first report of M. celatum IRD. Previous reports of M. celatum disease in HIV-1 patients have not presented data on the onset of disease relative to the commencement of ART. It is possible that some of these cases were IRD [7–9]. This case provides valuable information about the pathogenesis of IRD. Pulmonary inflammation, which on CT scanning was reported to be consistent with granulomatous inflammation, was associated with the repeated isolation of M. celatum from sputum and a cutaneous DTH response to tuberculin. Histopathological examination of the DTH reaction showed a tissue predominance of CD4 T cells, suggesting that the immune response was mediated by tuberculin-specific CD4 T cells. However, whole blood IFN-γ release assays demonstrated the presence of blood T cells responding to NTM antigens, presumably reflecting the presence of M. celatum-specific CD4 T cells crossreacting with antigens within tuberculin. The pulmonary inflammation was associated with persistent anaemia and leukopenia and increased inflammatory markers. Apart from prophylactic azithromycin, specific antimycobacterial therapy was not given to treat the pneumonitis. Corticosteroid therapy resulted in the resolution of the cytopenias and pulmonary lesions associated with the normalization of inflammatory markers. These findings highlight the importance of immunopathological responses to mycobacterial antigens and the efficacy of anti-inflammatory therapy in mycobacterial IRD.