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The IgD‐binding domain of the Moraxella IgD‐binding protein MID (MID 962‐1200 ) activates human B cells in the presence of T cell cytokines
Author(s) -
Nordström Therése,
Jendholm Johan,
Samuelsson Martin,
Forsgren Arne,
Riesbeck Kristian
Publication year - 2006
Publication title -
journal of leukocyte biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.819
H-Index - 191
eISSN - 1938-3673
pISSN - 0741-5400
DOI - 10.1189/jlb.0205065
Subject(s) - immunoglobulin d , biology , binding protein , immunology , microbiology and biotechnology , antibody , genetics , b cell , gene
Moraxella catarrhali s 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 (MID 962‐1200 ). To prove the specificity of MID 962‐1200 for IgD, a Chinese hamster ovary (CHO) cell line expressing membrane‐anchored human IgD was manufactured. MID 962‐1200 bound strongly to the recombinant IgD on CHO cells. Moreover, MID 962‐1200 stimulated peripheral blood lymphocyte (PBL) proliferation 5‐ and 15‐fold at 0.1 and 1.0 μg/ml, respectively. This activation could be blocked completely by antibodies directed against the CD40 ligand (CD154). MID 962‐1200 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 MID 962‐1200 , as revealed by a human cytokine protein array. MID 962‐1200 fused to green fluorescent protein (GFP) bound to human B cells and activated PBL to the same degree as MID 962‐1200 . Taken together, MID is the only IgD‐binding protein in Moraxella. Furthermore, the novel T cell‐independent antigen MID 962‐1200 may, together with MID 962‐1200 –GFP, be considered as promising reagents in the study of IgD‐dependent B cell activation.