The IgD-binding domain of the Moraxella IgD-binding protein MID (MID962-1200) activates human B cells in the presence of T cell cytokines.
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 (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 microg/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.
Nordström
Therése
T
Department of Laboratory Medicine, Malmö University Hospital, Lund University, SE-205 02, Malmö, Sweden.
Jendholm
Johan
J
Samuelsson
Martin
M
Forsgren
Arne
A
Riesbeck
Kristian
K
D018829:Adhesins, Bacterial / Q000276:immunology* / Q000494:pharmacology; D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D001402:B-Lymphocytes / Q000187:drug effects / Q000276:immunology*; D023201:CD40 Ligand / Q000187:drug effects / Q000276:immunology; D016466:CHO Cells; D002462:Cell Membrane / Q000276:immunology; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D006224:Cricetinae; D016207:Cytokines / Q000276:immunology / Q000494:pharmacology*; D049452:Green Fluorescent Proteins / Q000276:immunology; D006801:Humans; D007072:Immunoglobulin D / Q000276:immunology*; D015850:Interleukin-6 / Q000096:biosynthesis; D001936:Moraxella catarrhalis / Q000276:immunology*; D013601:T-Lymphocytes / Q000187:drug effects / Q000276:immunology*; D013997:Time Factors
D018829:Adhesins, Bacterial; D000906:Antibodies; D016207:Cytokines; C439616:IgD-binding protein MID, Moraxella catarrhalis; D007072:Immunoglobulin D; D015850:Interleukin-6; D023201:CD40 Ligand; D049452:Green Fluorescent Proteins