Follicular dendritic-like cells derived from human monocytes

Rapid de novo generation of antigen specific human B cells with expression of Blimp-1 and AID by in vitro immunization

In vitro immunization with antigens and cytokines triggers specific human B-cell response in short periods and is therefore superior to conventional in vivo immunization for antibody development. However, this new technology is limited by low efficiency, poor reproducibility, and requirement of pre-immunized lymphocytes. In this study, we demonstrate a novel method for de novo inducing antigen-specific human B cells in vitro. Unlike previous in vitro immunization of unfractionated PBMCs, we firstly optimized the conditions for inducing monocyte-derived dendritic cells (DCs) to efficiently capture, process, and present antigens. Instead of using the conventional method to activate Th2 cells for in vitro immunization, we succeeded to differentiate naïve CD4⁺ T cells into T follicular helper (Tfh) cells using antigen-sensitized DCs and cytokine cocktail. We discovered the differentiated T cells expressed ICOS, PD-1, BCL-6, and IL-21 at high levels. After 12 days of T-B co-culture, we observed induced T cells efficiently promoted naïve B cells to differentiate into plasmablasts secreting antigen-specific antibodies, with expression of Blimp-1 and AID related to affinity maturation and class switching. Thus, we established a new co-culture system with naïve lymphocyte populations for de novo acquisition of specifically in vitro immunized B cells potentially for development of therapeutic antibodies, which also provides novel insights into understanding the complex interactions among immune cells in lymph nodes.

Monocytes do not transdifferentiate into proper osteoblasts

Recent publications suggested that monocytes might be an attractive cell type to transdifferentiate into various cellular phenotypes. Aim was, therefore, to evaluate the potential of blood monocytes to transdifferentiate into osteoblasts. Monocytes isolated from peripheral blood were subjected to two previously published treatments to obtain unique, multipotent cell fractions, named programmable cells of monocytic origin (PCMOs) and monocyte-derived mesenchymal progenitor cells (MOMPs). Subsequently, MOMPs and PCMOs were treated with osteogenic differentiation medium (including either vitamin D or dexamethasone) for 14 days. Regarding a variety of surface markers, no differences between MOMPs, PCMOs, and primary monocytes could be detected. The treatment with osteogenic medium neither resulted in loss of hematopoietic markers nor in adoption of mesenchymal phenotype in all cell types. No significant effect was observed regarding the expression of osteogenic transcription factors, bone-related genes, or production of mineralized matrix. Osteogenic medium resulted in activation of monocytes and appearance of osteoclasts. In conclusion, none of the investigated monocyte cell types showed any transdifferentiation characteristics under the tested circumstances. Based on our data, we rather see an activation and maturation of monocytes towards macrophages and osteoclasts.

Expression of mesenchyme-specific gene signatures by follicular dendritic cells: insights from the meta-analysis of microarray data from multiple mouse cell populations

Follicular dendritic cells (FDC) are an important subset of stromal cells within the germinal centres of lymphoid tissues. They are specialized to trap and retain antigen-containing immune complexes on their surfaces to promote B-cell maturation and immunoglobulin isotype class-switching. However, little is known of the cell types from which FDC originate. To address fundamental questions associated with the relationships between FDC and other cell populations, we took advantage of the growing body of publicly available data for transcriptome analysis. We obtained a large number of gene expression data files from a range of different primary mouse cells and cell lines and subjected these data to network-based cluster analysis using BiolayoutExpress(3D) . Genes with related function clustered together in distinct regions of the graph and enabled the identification of transcriptional networks that underpin the functional activity of distinct cell populations. Several gene clusters were identified that were selectively expressed by cells of mesenchymal lineage and contained classic mesenchymal cell markers and extracellular matrix genes including various collagens, Acta2, Bgn, Fbn1 and Twist1. Our analysis showed that FDC also express highly many of these mesenchyme-associated genes. Promoter analysis of the genes comprising the mesenchymal clusters identified several regulatory motifs that are binding sites for candidate transcription factors previously known to be candidate regulators of mesenchyme-specific genes. Together, these data suggest FDC are a specialized mesenchymal cell population within the germinal centres of lymphoid tissues.

Splenic CD19-CD35+B220+ cells function as an inducer of follicular dendritic cell network formation

Follicular dendritic cells (FDCs) form a reticular FDC network in the lymphoid follicle that is essential for the retention and presentation of native antigens in the form of antigen-antibody immune complexes (ICs) to B cells during secondary immune response. Although the presence of migrating precursors of FDCs has been hypothesized, their entity has not been elucidated. Here we report the identification of murine splenic CD19(-)CD11c(-)CD35(+)B220(+) cells as an inducer of FDC network formation. We demonstrated that CD19(-)-CD11c(-)CD35(+)B220(+) cells, together with stromal cells, had the remarkable ability to form lymphoid-follicle-like structures that contained B220(+)FDC-M1(+) reticular cells originally derived from CD19(-)-CD11c(-)CD35(+)B220(+) cells in the CD35(+) reticulum. Our results indicate that CD19(-)CD11c(-)CD35(+)B220(+) cells function as an inducer of FDC network formation and that the interaction between CD19(-)CD11c(-)CD35(+)B220(+) cells and stromal cells is required to initiate lymphoid follicle formation.