Altered cellular infiltration and cytokine levels during early Mycobacterium tuberculosis sigC mutant infection are associated with late-stage disease attenuation and milder immunopathology in mice

<p>Abstract</p> <p>Background</p> <p>Mouse virulence assessments of certain <it>Mycobacterium tuberculosis </it>mutants have revealed an immunopathology defect in which high tissue CFU counts are observed but the tissue pathology and lethality are reduced. <it>M. tuberculosis </it>mutants which grow and persist in the mouse lungs, but have attenuated disease progression, have the immunopathology (<it>imp</it>) phenotype. The antigenic properties of these strains may alter the progression of disease due to a reduction in host immune cell recruitment to the lungs resulting in disease attenuation and prolonged host survival.</p> <p>Results</p> <p>In this study we focused on the mouse immune response to one such mutant; the <it>M. tuberculosis </it>Δ<it>sigC </it>mutant. Aerosol infection of DBA/2 and SCID mice with the <it>M. tuberculosis </it>Δ<it>sigC </it>mutant, complemented mutant and wild type strain showed proliferation of mutant bacilli in mouse lungs, but with decreased inflammation and mortality in DBA/2 mice. SCID mice shared the same phenotype as the DBA/2 mice in response to the Δ<it>sigC </it>mutant, however, they succumbed to the infection faster. Bronchoalveolar lavage (BAL) fluid analysis revealed elevated numbers of infiltrating neutrophils in the lungs of mice infected with wild type and complemented Δ<it>sigC </it>mutant strains but not in mice infected with the Δ<it>sigC </it>mutant. In addition, DBA/2 mice infected with the Δ<it>sigC </it>mutant had reduced levels of TNF-α, IL-1β, IL-6 and IFN-γ in the lungs. Similarly, there was a reduction in proinflammatory cytokines in the lungs of SCID mice. In contrast to the mouse model, the Δ<it>sigC </it>mutant had reduced initial growth in guinea pig lungs. A possible mechanism of attenuation in the Δ<it>sigC </it>mutant may be a reduction in neutrophilic-influx in the alveolar spaces of the lungs, and decreased proinflammatory cytokine secretion. In contrast to mouse data, the <it>M. tuberculosis </it>Δ<it>sigC </it>mutant proliferates slowly in guinea pig lungs, a setting characterized by caseating necrosis.</p> <p>Conclusion</p> <p>Our observations suggest that the immunopathology phenotype is associated with the inability to trigger a strong early immune response, resulting in disease attenuation. While macrophages and T cells have been shown to be important in containing <it>M. tuberculosis </it>disease our study has shown that neutrophils may also play an important role in the containment of this organism.</p

Pathogenesis of myelin oligodendrocyte glycoprotein induced experimental autoimmune encephalomyelitis in DBA/1 mice

Experimental autoimmune encephalomyelitis (EAE) is an animal model of the human autoimmune disease, multiple sclerosis (MS). MS is prevalent among the Caucasian population and linkage analysis studies have indicated that the presence of certain MHC class II genes can increase the risk of manifesting MS. Due to the limitations of MS patient materials, EAE has provided a tool for studying the mechanisms behind the initiation, progression and remission of MS and consequently providing information on how the immune system functions in MS. In this study, myelin oligodendrocyte glycoprotein (MOG) was used with adjuvant to induce EAE in the DBA/ 1 mouse strain. We established DBA/ 1 (H2q) mice as highly susceptible to MOG-induced EAE after screening several different MHC class II congenic mice. In additon, we also established the mildest immunization protocol to date using less or even omitting adjuvant components such as Mycobacterium tuberculosis (MT) and pertussis toxin (PT). Investigation of CD4 cell deficient mice (CD4-/-) and CD8 cell deficient mice (CD8-/-), as well as of wild type DBA/ 1 mice depleted of either CD4+ T cells or CD8+ T cells, highlighted the role of CD8+ T cells in MOG-induced EAE. Coadministration of PT appeared to alter EAE susceptibility by Increasing clinical severity when MOG peptide was used. Hence use of PT for the induction of EAE in mouse strains should be re-assessed as appropriate animal models of MS as the immunological mechanisms are skewed due to the action of PT. The role of B cells was investigated using µMT and xid (lacking a B cell subpopulation) mice immunized with MOG. Both µMT and xid mice developed MOG-EAE but with decreased clinical severity as well as less demyelination in the CNS. It can therefore be concluded that B cells do not have a primary role in disease initiation, but contribute to severity of pathogenesis. We next investigated the role of Fc receptors (FcRs), since FcRs link the cellular and the humoral branches of the immune system. FcR-gamma and Fc-gammaRII deficient mice were immunized with MOG. FcR-gamma deficient mice were protected from disease while Fc-gammaRII deficient mice had enhanced disease. Thus the role of FcRs in either enhancing or downregulating cell activation is an important mechanism in disease development. This thesis presents the DBA/ 1 mouse strain as a new animal model of EAE. Using different gene- deleted mice on the DBA/ 1 background has identified the different roles of T cell subsets, B cells and FcRs in the pathogenesis of EAE. Clearly to provide an entire picture of how EAE is initiated, an overall view of the interactions within the immune system is required. Comprehending the mechanisms involved in EAE may provide further insight into the human disease, MS

A comparative analysis of B cell-mediated myelin oligodendrocyte glycoprotein-experimental autoimmune encephalomyelitis pathogenesis in B cell-deficient mice reveals an effect on demyelination.

We have investigated the role of B cells in myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE) using B cell-deficient mice muMT) and mice bearing the X-linked immunodeficiency (xid). The mice were immunized with MOG(1-125 )in complete Freund's adjuvant but without use of pertussis toxin. B cell-deficient muMT mice on different genetic backgrounds (C57BL/10 and DBA/1 strains) developed EAE, although with a reduced clinical severity. Histological analyses revealed decreased demyelination in the central nervous system while the influx of inflammatory cells was similar or only slightly reduced as compared to B cell-sufficient control mice. Xid mice on the DBA/1 background also developed disease with a reduced disease severity. The anti-MOG antibody response in the xid mice was decreased, while the T cell response to MOG was unaffected. We thus demonstrate that B cells are not critical for the development of MOG-induced EAE but contribute to the severity. The contribution of B cells to pathogenesis appears to be mainly through demyelination rather than through inflammation