Ultrastructure of fibrous dysplasia of bone: a study of its fibrous, osseous, and cartilaginous components

Eight cases of fibrous dysplasia were evaluated by electron microscopy and the findings were correlated with the light microscopy. Fibroblasts and myofibroblasts were the cells seen in the fibrous component. The osseous component consisted of immature woven bone trabeculae lined by abnormal osteoblasts with a fibroblastlike appearance. The cartilaginous component resembled hyaline cartilage. The process of mineralization of both osseous and cartilaginous tissues appeared similar to normal bone and cartilage. In fibrous dysplasia there is a slow turnover of bone, and this correlates well with the flattened shape of the bone-lining cells. When compared with normal ossification, the process of bone formation appears to be arrested after an early stage resembling membranous ossification. It is possible that the abnormal osteoblastic maturation of the bone-forming mesenchyme is one of the most important alterations of this condition.

Dissection of the functions of antigen-presenting cells in the induction of T cell activation

The functions of antigen-presenting cells (APC) in the initiation of T cell activation was examined by culturing antigen-bearing guinea pig macrophages (M phi) with T cells obtained from antigen-primed animals. Although such antigen-bearing M phi stimulated primed syngeneic T cell DNA synthesis, as assessed by tritiated thymidine incorporation, paraformaldehyde fixation (0.15% for 1 min at 37 degrees C) abolished this capacity. Analysis with acridine orange staining indicated that fixed antigen-bearing M phi could not trigger primed syngeneic T cells to progress from the G0 to the G1 phase of the cell cycle. The addition of control non-antigen-bearing syngeneic or allogeneic M phi but not interleukin 1 or 2 to cultures of T cells and fixed APC permitted a proliferative response. Although the interaction between fixed antigen-bearing M phi and responding T cells was genetically restricted, there was no similar restriction for the supplemental control M phi. In fact, completely Ia-negative endothelial cells (EC) and fibroblasts (FB) could restore antigen responsiveness to cultures of fixed antigen-bearing M phi and syngeneic responding T cells, although they could not directly present antigen. Moreover, metabolically intact accessory cells, including Ia-negative EC and FB, could take up and process antigen to an immunogenic moiety, which fixed Ia-positive M phi could present to primed T cells. These data indicate that recognition of the antigen-Ia complex on an APC is necessary but not sufficient to trigger proliferation of freshly obtained primed T cells. The results additionally support the conclusion that APC carry out at least two separate functions necessary for the initiation of antigen-induced T cell activation. Not only must the APC display the antigen-Ia complex, but it must also convey another required effect. This influence, which apparently involved the establishment of cell to cell contact, was neither Ia nor antigen dependent and could only be provided by a metabolically intact cell. By contrast, genetically restricted antigen presentation could be accomplished by a fixed Ia-positive cell. Only when both the antigen-Ia complex and the influence of an intact accessory cell were provided by the same or different accessory cell were T cells triggered to enter the cell cycle.

Glycosaminoglycan distribution in substratum adhesion sites of aging human skin fibroblasts, including papillary and reticular subpopulations

Glycosaminoglycan (GAG) distribution has been analyzed in the adhesion sites, left substratum-bound after EGTA-mediated detachment, of various human skin fibroblast populations grown in vitro in the presence (asc+) or absence (asc-) of ascorbate. Examination of these skin fibroblasts during the EGTA treatment by scanning electron microscopy reveals that (a) asc+ cells detach much more rapidly than asc- cells, but (b) asc- or asc+ cells leave the same two types of structures in longterm culture-generated substratum-attached material (L-SAM)--long linear retraction fibers and "footpad-like" structures. Most of the [3H]glucosamine-radiolabeled polysaccharides in L-SAM were shown to be GAGs. Fibroblasts from a full-thickness skin sample from a very young patient (AG4449) have similar distributions of the GAGs in both the EGTA-suspended cell and L-SAM fractions; however, asc+ cell and L-SAM fractions contain relatively more heparan sulfate than the asc- fractions. In contrast, full-thickness skin fibroblasts from an elderly patient (AG2261) generate GAG distributions in their L-SAMs (with greatly elevated levels of hyaluronate and chondroitin sulfate) that are very different from those of the cell fractions and from those of AG4449; furthermore, these distributions in AG2261 fractions do not change when shifted from asc- to asc+ medium. These studies led to analyses of the two major fibroblast subsets--papillary (PAP) or reticular (RET)--that can be isolated from the dermis of a newborn infant (patient 5). The GAG distributions in the RET fractions were different from those in PAP fractions; of special note was the greater length of heparan sulfate chains from all RET fractions examined when compared to PAP fractions. There was a remarkable similarity in the GAG distributions of asc+ RET fractions when compared to the full-thickness AG2261 cell fractions. In summary, these studies demonstrate that asc- or asc+ "young" cells generate different GAG distributions in their substratum adhesion sites, whereas "old" cells from a full-thickness skin sample do not alter their distribution when shifted from asc- to asc+ (this distribution is different from that of "young" cells). Furthermore, analyses of GAGs in papillary and reticular cell fractions reveal significant differences between the two, with considerable similarity of asc+ reticular fractions to the full-thickness AG2261 fibroblasts, which is consistent with the enrichment of reticular fibroblasts in the skin of aging individuals.

Subpopulations of fibroblasts from mouse skeletal muscle defined by clonal variation for 5' nucleotidase expression

A primary cloning technique has been employed for the isolation of nine spontaneously transformed cell lines from mouse skeletal muscle. Four of these lines were isolated after selection for partial resistance to the purine (adenine) analog 2'6'diaminopurine and five were isolated from non-selected control dishes. Four of the nonselected lines and three of the selected lines demonstrated a fibroblastoid morphology in vitro. The other two cell lines (one from each group) were epithelioid. Two of the three selected fibroblastoid lines were found to contain significant quantities of the enzyme 5'nucleotidase (EC3.1.3.5), whereas the four nonselected fibroblastlike lines, one selected fibroblastlike line, and the two epithelioid lines did not. In the two cell lines expressing 5'nucleotidase activity, this expression was stable in the absence of selective pressure. Histochemical staining of mouse skeletal muscle for 5'nucleotidase activity demonstrated positive staining in the cells of small blood vessels and in a subset of the connective tissue cells. The bulk of the skeletal muscle tissue, however, had no detectable 5'nucleotidase activity. We propose that the two cultivatable types of fibroblastoid cell lines represent distinct classes of fibroblastlike cells in vivo, reflecting alternative states of stable cellular differentiation involving 5'nucleotidase expression.

Subdivision of S-phase and its use for comparative purposes in cultured human cells

Intranuclear DNA synthesis and concomitant chromosome duplication occur during a discrete period of the cell cycle termed S-phase. Using replication-banding and serial time sampling in asynchronous cell populations, it is possible to subdivide the S-phase into four or five chronological compartments termed "subphases". This paper discusses methods for analysing the sampling data to obtain the average duration of these subphases and the positions within S of the borders between them. Such information not only allows a more detailed analysis of the cell cycle, but also provides parameters which can be used for rigorous comparisons of cell populations from different sources and experimental conditions. Examples are given of application of the method to normal and chromosomally abnormal primary human fibroblasts and lymphocytes growing in short-term in vitro culture.

Immunocytochemical characterisation of cell cultures grown from dissociated 1-2-day post-natal rat cerebral tissue. A developmental study

A range of cell-specific markers have been employed with immunocytochemical methods to characterise and quantitate the cell types present in mixed brain cell cultures derived from dissociated 1-2-day post-natal rat cerebral hemispheres and grown in the presence of FCS. Protoplasmic astrocytes (GFAP+, A2B5-) were the major cell type to develop in culture, a confluent monolayer forming in 5-8 days. A population of smaller round cells of oligodendrocyte-like morphology appeared on this astrocyte layer. Greater than 70% of these smaller cells were GC- and thus were not oligodendrocytes. The GC- cells were A2B5+ and, in early cultures, may therefore be progenitor glial cells. Examination of GFAP and A2B5 co-expression by these smaller cells was difficult due to the dense underlying GFAP+ astrocyte layer. In less dense areas of older cultures these smaller cells with processes were GFAP+ and A2B5+: these are Type 2, fibrous astrocytes. GC+ oligodendrocytes, comprising 5-10% of the total identified cell population, were initially distributed over the astrocyte monolayer; in older cultures (after about 8 days) GC+ cells were observed in clumps over places where NF+ cells were identifiable. Such GC+ cells mostly became MBP+. Neurones accounted for about 6% of the identifiable cells in early cultures but a lower percentage in older cultures. Minor populations of ependymal cells and macrophages were present; cells displaying fibronectin, fibroblasts, were rarely identified. Use of horse serum in place of FCS gave lower yields of GC+ cells in cultures, slowed down astrocyte development, and resulted in the formation of trunks of GFAP+ cells throughout cultures. Other sera gave lower numbers of GC+ cells.

Quantitative morphological analysis of proliferating and nonproliferating subpopulations of IMR-90 fibroblasts during aging in vitro

Early-, mid- and late-passage cultures (population doubling levels 12, 35, and 51, respectively) of IMR-90 fibroblasts were exposed to 3H-thymidine for 48 h prior to fixation in situ for morphometric analysis in order to determine quantitatively what ultrastructural changes accompany the loss of proliferative capacity during aging in vitro. Analysis of autoradiographs, both at the light and electron microscopic levels, with an image analyzer followed by ANOVA statistical scrutiny demonstrated that a significant increase in relative cell area, an indicator of cell size, was characteristic of cells unable to incorporate 3H-TdR at both mid- and late-passage, but not at early-passage levels. Nuclear size also increased significantly with progressive passage level but was not related to proliferative capacity. No significant difference in the area fraction of nucleoli per unit area of nucleus or of mitochondria, Golgi, or lysosomes was seen in either subpopulation at any passage level. Dilated cisternae of rough endoplasmic reticulum in early-passage cells were seen if cells were harvested with trypsin and fixed either before or after centrifugation, but were not seen in labeled or unlabeled cells from any passage level when cultures were fixed in situ. We conclude that a significant increase in cell size is the only significant morphological change associated with the loss of proliferative capacity of IRM-90 fibroblasts. Furthermore, our data indicate that there is no accumulation of secondary lysosomes in human diploid fibroblasts during aging in vitro; we therefore cannot support any hypothesis of aging or proliferative decline that is based mechanistically upon this phenomenon.