title: The mucosal adjuvant macrophage-activating lipopeptide-2 directly stimulates B lymphocytes via the TLR2 without the need of accessory cells.
abstract: The macrophage-activating lipopeptide-2 (MALP-2) is an agonist of the TLR heterodimer 2/6, which exhibits potent activity as mucosal adjuvant, promoting strong humoral and cellular responses. Although B cells expressing TLR2/6 are potential targets, very little is known about the effect of MALP-2 on B cells. Studies were performed using total spleen cells or purified B cells from WT mice or animals deficient in TLR2, T cells, B cells, or specific subpopulations of B cells. They demonstrated that MALP-2 promotes a T cell-independent activation and maturation of B cells (mainly follicular but also B-1a and marginal zone B cells) via TLR2. MALP-2 also increased the frequency of IgM- and IgG-secreting cells, but bystander cells were required for IgA secretion. Activated B cells exhibited increased expression of activation markers and ligands that are critical for cross-talk with T cells (CD19, CD25, CD80, CD86, MHC I, MHC II, and CD40). Immunization of mice lacking T cells showed that MALP-2-mediated stimulation of TLR2/6 was unable to circumvent the need of T cell help for efficient Ag-specific B cell activation. Immunization of mice lacking B cells demonstrated that B cells are critical for MALP-2-dependent improvement of T cell responses. The knowledge emerging from this work suggests that MALP-2-mediated activation of B cells through TLR2/6 is critical for adjuvanticity. B cell stimulation by pattern recognition receptors seems to be a basic mechanism that can be exploited to improve the immunogenicity of vaccine formulations.
authors.affiliation: Vaccine Research Group, Division of Microbiology and Molecular Immunology Group, Division of Molecular Biotechnology, GBF-German Research Centre for Biotechnology, Braunschweig, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Borsutzky
authors.forename: Karsten
authors.initials: K
authors.lastname: Kretschmer
authors.forename: Pablo D
authors.initials: PD
authors.lastname: Becker
authors.forename: Peter F
authors.initials: PF
authors.lastname: Mühlradt
authors.forename: Carsten J
authors.initials: CJ
authors.lastname: Kirschning
authors.forename: Siegfried
authors.initials: S
authors.lastname: Weiss
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Guzmán
mesh_terms: D000276:Adjuvants, Immunologic / Q000502:physiology*; D000818:Animals; D000938:Antigen-Presenting Cells / Q000276:immunology; D001402:B-Lymphocytes / Q000276:immunology* / Q000378:metabolism; D015415:Biomarkers / Q000378:metabolism; D049109:Cell Proliferation; D002478:Cells, Cultured; D018928:Immunity, Mucosal / Q000235:genetics; D055666:Lipopeptides; D008074:Lipoproteins / Q000502:physiology*; D008213:Lymphocyte Activation / Q000235:genetics / Q000276:immunology*; D008262:Macrophage Activation / Q000276:immunology*; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008819:Mice, Nude; D009842:Oligopeptides / Q000502:physiology*; D011971:Receptors, Immunologic / Q000502:physiology*; D013154:Spleen / Q000166:cytology / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology / Q000378:metabolism; D051195:Toll-Like Receptor 2
chemical_list: D000276:Adjuvants, Immunologic; D015415:Biomarkers; D055666:Lipopeptides; D008074:Lipoproteins; D009842:Oligopeptides; D011971:Receptors, Immunologic; C493486:Tlr2 protein, mouse; D051195:Toll-Like Receptor 2; C106335:macrophage stimulatory lipopeptide 2