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- Nordström, Therése, et al.
(author)
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Ionic binding of C3 to the human pathogen Moraxella catarrhalis is a unique mechanism for combating innate immunity
- 2005
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In: Journal of Immunology. - 1550-6606. ; 175:6, s. 3628-3636
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Journal article (peer-reviewed)abstract
- Moraxella catarrhalis ubiquitous surface proteins A1 and A2 (UspA1/A2) interfere with the classical pathway of the complement system by binding C4b-binding protein. In this study we demonstrate that M. catarrhalis UspA1 and A2 noncovalently and in a dose-dependent manner bind both the third component of complement (C3) from EDTA-treated serum and methylamine-treated C3. In contrast, related Moraxella subspecies (n = 13) or other human pathogenic bacteria (n = 13) do not bind C3 or methylamine-treated C3. Experiments with recombinant proteins and M. catarrhalis mutants devoid of UspA1/A2 revealed that UspA1/A2 exert their actions by absorbing and neutralizing C3 from serum and restrain complement activation. UspA2 was responsible for most of the effect, and the Moraxella mutant lacking UspA2 was more sensitive to the lytic effect of human serum compared with the wild type. Interestingly, among the large number of bacteria analyzed, only M. catarrhalis has this unique ability to interfere with the innate immune system of complement by binding C3.
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| 2. |
- Nordström, Therése
(author)
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MORAXELLA CATARRHALIS OUTER MEMBRANE PROTEINS AND INTERACTIONS WITH THE HUMAN IMMUNE SYSTEM
- 2005
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Doctoral thesis (other academic/artistic)abstract
- Moraxella catarrhalis is frequently colonizing the human respiratory tract, particularly in children. This gram-negative bacterium has during the last two decades been recognized as a pathogen causing otitis media in children and lower respiratory tract infections in adults with predisposing conditions such as chronic obstructive pulmonary disease (COPD). The virulence determinants of M. catarrhalis are believed to be the lipooligosaccharide and the outer membrane proteins. Three important outer membrane proteins are Moraxella IgD-binding protein (MID), the ubiquitous surface proteins (Usp) A1 and A2. MID is an adhesin and it binds to IgD in a non-immune manner. We show that the mid gene was highly conserved, and that the MID expression varied without relation to the anatomical site of isolation or geographical origin of the isolates. The expression was also shown to be controlled by a poly(G)tract downstream of the startcodon. The region of MID with essentially preserved IgD-binding was determined to be located between the amino acid residues 962-1200 and was designated MID962-1200. MID962-1200 was shown to be a tetramer in native conditions and interestingly, this tetrameric form bound IgD 23-fold more efficiently than the monomeric form. Moreover, MID962-1200 stimulated purified B cells to proliferate independently of T cells. However, addition of IL-4 or IL-2 was required for efficient proliferation. We have also shown that M. catarrhalis interferes with both the classical and the alternative pathway of the complement system. It bound to the fluid phase inhibitor C4b-binding protein (C4BP) and the binding was mediated through UspA1 and UspA2. Importantly, C4BP retained its activity when bound to the surface of M. catarrhalis and was thus able to inhibit the activation through the classical pathway. We also showed that M. catarrhalis have the capacity to absorb C3 from serum independently of complement activation and UspA2 was determined to be the major binder of C3. In summary, MID is widely distributed among different M. catarrhalis strains. The IgD-binding region of MID is located between the amino acid residues 962-1200 and stimulates B cells independently of T cells. Finally, the M. catarrhalis outer membrane proteins UspA1 and UspA2 interfere with the complement system by binding C4BP and C3.
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| 3. |
- Nordström, Therése, et al.
(author)
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The IgD-binding domain of the Moraxella IgD-binding protein MID (MID962-1200) activates human B cells in the presence of T cell cytokines.
- 2006
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In: Journal of Leukocyte Biology. - : Oxford University Press (OUP). - 1938-3673 .- 0741-5400. ; 79:2, s. 319-329
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Journal article (peer-reviewed)abstract
- Moraxella catarrhalis immunoglobulin D (IgD)-binding protein (MID) is an outer membrane protein with specific affinity for soluble and cell-bound human IgD. Here, we demonstrate that mutated M. catarrhalis strains devoid of MID show a 75% decreased activation of human B cells as compared with wild-type bacteria. In contrast to MID-expressing Moraxella, the MID-deficient Moraxella mutants did not bind to human CD19(+) IgD(+) B cells. The smallest MID fragment with preserved IgD-binding capacity comprises 238 amino acids (MID962-1200). To prove the specificity of MID962-1200 for IgD, a Chinese hamster ovary (CHO) cell line expressing membrane-anchored human IgD was manufactured. MID962-1200 bound strongly to the recombinant IgD on CHO cells. Moreover, MID962-1200 stimulated peripheral blood lymphocyte (PBL) proliferation 5- and 15-fold at 0.1 and 1.0 mu g/ml, respectively. This activation could be blocked completely by antibodies directed against the CD40 ligand (CD154). MID962-1200 also activated purified B cells in the presence of interleukin (IL)-2 or IL-4. An increased IL-6 production was seen after stimulation with MID962-1200, as revealed by a human cytokine protein array. MID962-1200 fused to green fluorescent protein (GFP) bound to human B cells and activated PBL to the same degree as MID962-1200 Taken together, MID is the only IgD-binding protein in Moraxella. Furthermore, the novel T cell-independent antigen MID962-1200 may, together with MID962-1200-GFP, be considered as promising reagents in the study of IgD-dependent B cell activation.
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