ABSTRACT
Prevalence of Mycobacterium abscessus infections is increasing in patients with respiratory comorbidities. After initial colonisation, M. abscessus smooth colony (S) variants can undergo an irreversible genetic switch into highly inflammatory, rough colony (R) variants, often associated with a decline in pulmonary function. Here, we use an adult zebrafish model of chronic infection with R and S variants to study M. abscessus pathogenesis in the context of fully functioning host immunity. We show that infection with an R variant causes an inflammatory immune response that drives necrotic granuloma formation through host TNF signalling, mediated by the tnfa, tnfr1 and tnfr2 gene products. T cell-dependent immunity is stronger against the R variant early in infection, and regulatory T cells associate with R variant granulomas and limit bacterial growth. In comparison, an S variant proliferates to high burdens but appears to be controlled by TNF-dependent innate immunity early during infection, resulting in delayed granuloma formation. Thus, our work demonstrates the applicability of adult zebrafish to model persistent M. abscessus infection, and illustrates differences in the immunopathogenesis induced by R and S variants during granulomatous infection.
Subject(s)
Granuloma/immunology , Mycobacterium Infections, Nontuberculous/immunology , Mycobacterium abscessus/pathogenicity , Persistent Infection/immunology , Animals , Animals, Genetically Modified , Bacterial Proteins/genetics , Bacterial Proteins/metabolism , Disease Models, Animal , Gene Knockdown Techniques , Granuloma/microbiology , Granuloma/pathology , Host-Pathogen Interactions/immunology , Humans , Immunity, Innate , Lymphocyte Activation , Mycobacterium Infections, Nontuberculous/microbiology , Mycobacterium Infections, Nontuberculous/pathology , Mycobacterium abscessus/genetics , Mycobacterium abscessus/immunology , Persistent Infection/microbiology , Persistent Infection/pathology , Signal Transduction/immunology , T-Lymphocytes, Regulatory/immunology , Tumor Necrosis Factor-alpha/metabolism , Zebrafish , Zebrafish Proteins/metabolismABSTRACT
Fuhrmann syndrome and the Al-Awadi/Raas-Rothschild/Schinzel phocomelia syndrome are considered to be distinct limb-malformation disorders characterized by various degrees of limb aplasia/hypoplasia and joint dysplasia in humans. In families with these syndromes, we found homozygous missense mutations in the dorsoventral-patterning gene WNT7A and confirmed their functional significance in retroviral-mediated transfection of chicken mesenchyme cell cultures and developing limbs. The results suggest that a partial loss of WNT7A function causes Fuhrmann syndrome (and a phenotype similar to mouse Wnt7a knockout), whereas the more-severe limb truncation phenotypes observed in Al-Awadi/Raas-Rothschild/Schinzel phocomelia syndrome result from null mutations (and cause a phenotype similar to mouse Shh knockout). These findings illustrate the specific and conserved importance of WNT7A in multiple aspects of vertebrate limb development.
