An immunoelectron-microscopic study of class II major histocompatibility complex molecule-expressing macrophages and dendritic cells in experimental rat periapical lesions

Gene expression analysis of immunostained endothelial cells isolated from formaldehyde-fixated paraffin embedded tumors using laser capture microdissection--a technical report

Laser capture microdissection (LCM) allows microscopic procurement of specific cell types from tissue sections that can then be used for gene expression analysis. In conventional LCM, frozen tissues stained with hematoxylin are normally used to the molecular analysis. Recent studies suggested that it is possible to carry out gene expression analysis of formaldehyde-fixated paraffin embedded (FFPE) tissues that were stained with hematoxylin. However, it is still unclear if quantitative gene expression analyses can be performed from LCM cells from FFPE tissues that were subjected to immunostaining to enhance identification of target cells. In this proof-of-principle study, we analyzed by reverse transcription-PCR (RT-PCR) and real time PCR the expression of genes in factor VIII immunostained human endothelial cells that were dissected from FFPE tissues by LCM. We observed that immunostaining should be performed at 4 degrees C to preserve the mRNA from the cells. The expression of Bcl-2 in the endothelial cells was evaluated by RT-PCR and by real time PCR. Glyceraldehyde-3-phosphate dehydrogenase and 18S were used as house keeping genes for RT-PCR and real time PCR, respectively. This report unveils a method for quantitative gene expression analysis in cells that were identified by immunostaining and retrieved by LCM from FFPE tissues. This method is ideally suited for the analysis of relatively rare cell types within a tissue, and should improve on our ability to perform differential diagnosis of pathologies as compared to conventional LCM.

Antigen-presenting cells in human radicular granulomas

Substantial numbers of dendritic cells have been detected in radicular granulomas. To test the hypothesis that local antigen presentation from dendritic cells to T-cells is involved critically in immunological responses within radicular granulomas, we compared characteristics of dendritic cells and macrophages by morphological and biological analyses. Under light microscopy, HLA-DR+ and CD68+ cells showed diverse profiles, including dendritic-shaped cells. Transmission electron microscopy revealed that HLA-DR+ dendritic cells, with long cytoplasmic processes and lacking distinct phagosomes, were concentrated in the lymphocyte-rich area. HLA-DR alpha-chain, CD83, and CD86 mRNAs from HLA-DR+ dendritic cells, and CD28 mRNA from CD28+ T-cells were up-regulated in lymphocyte-rich area. Scanning electron microscopy demonstrated that the density of gold particles on dendritic cells was higher than that on HLA-DR+ macrophages. These results suggest that dendritic cells in radicular granulomas are associated with local defense reactions as stronger antigen-presenting cells, as compared with macrophages.

Characteristics of resident dendritic cells in various regions of rat periodontal ligament

In the periodontal ligament (PDL) of normal rat molars, a considerable number of dendritic cells (DCs) are distributed as resident immunocompetent cells. We have hypothesized that the resident type of DCs can alter their morphology and phenotype to adapt to the microenvironment of the PDL. Thus, we have compared the characteristics of DCs in various regions of rat PDL by immunoelectron microscopy and gene expression analysis by means of reverse transcription/polymerase chain reaction. DCs in the periapical region show immature characteristics, i.e., small round profiles and few organelles. In the mesial region, which is the most stable area in the PDL, the density of DCs is the highest. DCs in the furcal region show the characteristics of activated antigen-presenting cells, i.e., CD86(high) expression, electron-dense lysosomes, and cell-to-cell contacts with lymphocytes. When the PDL is bacterially challenged by pulp exposure, the number of CD86+ DCs and contacts with lymphocytes increase in the furcal region. Gene expression analysis for the furcal region has also shown the up-regulation of the major histocompatibility complex class II alpha-chain, CD83, CD86, and the antigen-presenting cell-lectin-like receptor A1. Thus, we have demonstrated heterogeneity in resident DCs. This may be associated with the difference in DCs regarding their state of maturation/activation, which may further reflect microenvironmental differences such as the amount of external antigens.

Kinetics of RANKL, RANK and OPG expressions in experimentally induced rat periapical lesions

OBJECTIVE

The object of this study was to elucidate the kinetics of receptor activator of NFkB ligand (RANKL), RANK, osteoprotegerin (OPG), and cytokine expressions in experimentally induced rat periapical lesions.

STUDY DESIGN

The mRNA expressions of RANKL, RANK, OPG, and cytokines in experimentally induced rat periapical lesions were evaluated by real-time PCR. The lesions were induced in male Wistar rats (n = 48, 5 weeks of age) by unsealed pulp exposure of the lower first molars.

RESULTS

Expression of RANKL was up-regulated at the beginning of lesion expansion, and expression ratio of RANKL against OPG, a competitor of RANKL, peaked at 2 and 3 weeks. Expression of inflammatory cytokines, such as TNF-alpha, IL-1alpha, and IL-1beta also increased at this stage, suggesting contribution of synergic effects of RANKL and proinflammatory cytokine signaling to lesion expansion. Most of RANKL+ cells were fibroblastic, but few of them were T cells.

CONCLUSION

Expression of RANKL and proinflammatory cytokines was correlated with periapical lesion expansion.

Heterogeneity of dendritic cells in rat apical periodontitis

Dendritic cells are important for the induction of T-lymphocyte-mediated immunity by acting as antigen-presenting cells. We have previously reported that dendritic cells are prevalent in the chronic non-expanding phase of rat apical periodontitis. To characterize these cells further, immunoelectron microscopy with three dendritic cell markers (CD11c, OX6, OX62) was conducted for samples from rat models of apical periodontitis. Dendritic cells were divided into two types (type I or type II). Most of the type I dendritic cells expressed CD11c, showed an irregular large profile, had typical cytoplasmic processes, and were recognized as the major dendritic cell population. Most of the type II dendritic cells expressed OX62, showed oval small profiles with a few thin short processes, and were sometimes observed infiltrating from blood vessels. Cell-to-cell contacts between type I dendritic cells and lymphocytes were the most frequently observed associations. These results suggest that dendritic cells are composed of heterogeneous populations that exhibit different phenotypes, morphologies, and maturation/differentiation/activation.

Immunoexpression of the HLA-DR class II molecule in cells from inflamed dental pulp

BACKGROUND

Despite that the role of inflammatory cells in chronic inflammatory reactions of pulpal origin (CIRPOs) has been extensively studied, function of the HLA-DR+ cells (HLA-DR+ Cs) is poorly understood. The aim of this study was to quantify their number and clarify their role in these lesions.

METHODS

We studied 11 CIRPOs immunostained with an anti-HLA-DR class II monoclonal antibody and the number and location of the HLA-DR+ Cs quantified. CIRPOs were divided in periapical granulomas (PGs), epithelized granulomas (EGs) and periapical cysts (PCs).

RESULTS

HLA-DR+ Cs were observed within epithelium, inflammatory infiltrate and close to blood vessels. In PGs, they account for 19-256 cells/mm2, in EGs they were 20-494 cells/mm2 and in PCs quantification numbered 39-316 cells/mm2.

CONCLUSIONS

Our results suggest that HLA-DR+ Cs present antigens to lymphocytes, collaborating in initiation, regulation, development and perpetuation of CIRPOs. Also, these results suggest that these cells have an active role during initiation of epithelial proliferation in PGs and that they are partially responsible for cystic transformation from EGs to periapical cysts. They may also play an active role in bone resorption.