Follicular dendritic cells (FDC) are involved in the presentation of native Ags to B cells during the secondary immune response. Some authors consider FDC to be hemopoietic cells, whereas others believe them to be mesenchymal cells. The low proportion of FDC in the lymphoid follicle, together with technical difficulties in their isolation, make these cells difficult to study. We show that Fibroblast Medium can be used successfully to isolate and maintain FDC lines. In this culture medium, we obtained 18 FDC lines from human tonsils, which proliferated for as long as 18 wk and showed a stable Ag phenotype as detected by flow cytometry and RT-PCR. FDC lines were CD45-negative and expressed Ags associated to FDC (CD21, CD23, CD35, CD40, CD73, BAFF, ICAM-1, and VCAM-1) and Ags specific for FDC (DRC-1, CNA.42, and HJ2). These cell lines were also able to bind B cells and secrete CXCL13, functional activities characteristic of FDC. Nevertheless, the additional expression of STRO-1, together with CD10, CD13, CD29, CD34, CD63, CD73, CD90, ICAM-1, VCAM-1, HLA-DR, alkaline phosphatase, and α-smooth muscle actin (α-SM actin) indicated that FDC are closely related to bone marrow stromal cell progenitors. The expression of α-SM actin also relates FDC with myofibroblasts. Like myofibroblasts, FDC lines expressed stress fibers containing α-SM actin and were able to contract collagen gels under the effect of TGFβ1 and platelet-derived growth factor. These findings suggest that FDC are a specialized form of myofibroblast and derive from bone marrow stromal cell progenitors.

Our results suggest the existence of a network in which hormones together with cytokines regulate the expression of HLA-G by DSC, and that may be of relevance in the maintenance of maternal-fetal tolerance.

Decidual stromal cells (DSC) are the main cellular component of the human decidua, but thus far their ascription to a given cell lineage is uncertain. In previous studies, these cells have been isolated and maintained in culture, and their antigen phenotype has been analysed to determine their affiliation. However, the presence in the culture medium of high proportions of fetal calf serum (FCS) may inhibit the expression of some surface antigens. In the present study, we show by flow cytometry that CD34 is rapidly down-regulated in human DSC cultured in RPMI 1640 with 20% FCS. For this reason, we used fibroblast medium, which contains only a small proportion (2%) of FCS, to isolate and culture these cells. Under these conditions DSC exhibited a stable antigen phenotype highly similar to that of these cells in vivo. Flow cytometry results confirmed that DSC cultured in fibroblast medium expressed CD34 protein, and reverse transcription-polymerase chain reaction findings showed that they have CD34 mRNA. Decidual stromal cells were also positive for STRO-1, an antigen that identifies stromal precursors of the bone marrow which also expresses CD34. The expression of CD10, CD13, alkaline phosphatase and alpha-smooth muscle actin by DSC, and the absence of expression of CD14 and CD45, further confirmed their relationship with the stromal precursors.

We determined the HLA frequency distribution in a sample of 100 Bubi individuals born on the island of Bioko (Equatorial Guinea). HLA-A, -B and -C typing was performed by serology and PCR-SSP. DRB1/3/4/5, DQB1 and DQA1 alleles were determined by PCR-SSOP. The HLA allele distribution of this population group resembles those found in other Bantu-speaking groups; however, the higher frequency of A30, A32, B44, DRB1*1301 in the Bubi with respect to other Bantu groups and the absence of DR4 deserve special mention. The cloning and sequencing of class I and II genes in this population allowed the description of five new allelic variants: B*4407, Cw*0706, Cw*1801, Cw*1802 and DQB1*0612 and five confirmatory sequences: B*3910, B*5703, B*8101, Cw*1203 and Cw*1701. The following new HLA-C,B haplotypes have been found in Bubi: Cw*08-B*57, Cw*18-B*57, Cw*0302-B*53, Cw*07-B*53 and Cw*1601-B*63. The most frequent seven-locus haplotype is: A*30-Cw*17-B*42-DRB1*1102-DRB3*0202-DQA1*05-DQB1 *0301. In terms of genetic distance, the Bubi are closer to other Bantu groups than to West African populations.

We previously demonstrated that human decidual stromal cells (DSC), the main cellular component of the decidua, are similar in antigen phenotype and structure to myofibroblasts, cells with contractile activity. In this work we isolated and maintained DSC in fibroblast medium, in which these cells show a stable phenotype similar to that of DSC in vivo. Flow cytometric observations showed that most DSC expressed alpha-smooth muscle (alpha-SM) actin, an intermediate filament that is considered a marker of myofibroblasts and is responsible for the contractile activity of these cells. alpha-SM actin mRNA was detected by RT-PCR in these cells. The contractile activity of DSC was determined by the gel contraction assay; we found that TGF beta 1 and platelet-derived-growth factor, cytokines that are known to be inducers of myofibroblast contractility, also induced contractility of DSC. IL-2, a Th1 cytokine-related with spontaneous abortion, also activated DSC contractility. Our results confirmed that DSC are phenotypically and functionally related with myofibroblast.

A novel HLA-DQB1 allele was detected by oligotyping in the Bubi population of Equatorial Guinea. In order to characterize the new allelic variant, a RT-PCR method which permitted the cloning of its complete coding region was designed. With this method, we have determined the nucleotide sequence of the new DQB1*0612 allele, related to *0604 and *0609 but differing from them at polymorphic codon 70. A proposal for the improvement of the sequencing strategies of HLA class II alleles is made.

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