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L J Simar

Publications and source records attributed to L J Simar.

At least 37 records · Page 2Linked to original sources
PubMed1986

Lipopolysaccharide suppresses immune complex retention by follicular dendritic cells without cytological alterations.

Follicular dendritic cells (FDC) are peculiar cells only located inside lymph follicles and which may be characterized by complex dendritic evaginations retaining high quantities of immune complexes by Fc and C3b receptors. After lipopolysaccharide (LPS) injection in mice the retention of gold-labelled immune complexes was abolished in draining lymph nodes. In order to examine the possibility that the transport of immune complexes to lymph follicles was impaired, we isolated FDC from lymph nodes and incubated them in presence of gold-labelled complexes: no or strongly reduced retention was then observed at the ultrastructural level. This LPS-induced impairment of immune complex fixation by FDC is not due to morphological alteration to the cells but to the inhibition of their Fc and C3b receptors. Further, LPS induces changes in the composition of the lymphocyte population in lymph follicles as higher numbers of blast cells and plasmocytes are observed after treatment.

Animals↗
PubMed1986

Transfer of immune complexes from lymphocytes to follicular dendritic cells.

Antigens in the form of immune complexes are retained on the membranes of follicular dendritic cells (FDC) for long periods of time. To examine how immune complexes reach germinal centers, where FDC are located, we injected mice with anti-2,4-dinitrophenyl (DNP) antibodies complexed to DNP-myoglobin-coated gold particles. The distribution of the particles in spleens or draining lymph nodes was then determined with the electron microscope. The vast majority of the particles were cell bound. Shortly after injection they were phagocytized by macrophages or fixed on lymphocytes. The latter were found even in the corona of lymph follicles but not in germinal centers. Already 30 min after injection, FDC in contact with the corona were faintly positive but were negative in the center. FDC precursor cells were occasionally observed but in too small a number to account for the transport of immune complexes to the germinal centers. Twenty-four hours after injection colloidal gold particles were found in phagolysosomes of macrophages or on cytoplasmic extensions of FDC in all parts of the germinal centers. Experiments performed on isolated FDC showed that they are not only able to take up free immune complexes but are also able to adsorb immune complexes from pulsed lymphocytes. These results strengthen the idea that lymphoid cells binding immune complexes by their Fc receptors may transport these complexes inside germinal centers.

Animals↗
PubMed1986

Retention of immune complexes by murine lymph node or spleen follicular dendritic cells. Role of antibody isotype.

Using monoclonal anti-trinitrophenyl (TNP) antibodies complexed to TNP-myoglobin-coated gold particles, we analysed at the ultrastructural level the retention by follicular dendritic cells (FDC) of immune complexes containing various antibody isotypes. Gold-labelled immune complexes were injected subcutaneously or intravenously into naive mice and, after 24 h, germinal centres of draining lymph nodes or spleen were examined by electron microscopy. FDC generally retained complexes containing IgG2a and IgG2b better than those formed with IgG1 or IgG3. IgM was rarely retained. FDC isolated from lymph nodes or spleens were incubated in vitro with gold-labelled complexes in a serum-free medium. IgG2a and IgG2b complexes were also retained in vitro in large quantities by FDC; IgG1 and IgG3 complexes were retained in smaller quantities or in highly variable quantities compared with IgG2; IgM complexes were rarely seen on FDC. There was no difference between FDC isolated from lymph nodes or from spleen with respect to the Ig isotypes required for Fc-mediated retention of immune complexes.

Animals↗
PubMed1986

[Influence of follicular dendritic cells on the survival of lymphocytes in vitro].

To study the role of follicular dendritic cells (FDC) in germinal centers, we tried to keep them alive in vitro by culturing entire lymphoid follicles. Ultrastructural studies of those cultures in different conditions of culture technique, medium and temperature have been made. In any considered conditions living FDC were not found in the cultures after the 7th day. But during that period, only lymphocytes in close contact with the cytoplasmic processes of FDC survived. FDC seem thus to exert a positive action on lymphocyte survival in vitro. Moreover, FDC and lymphocytes appeared associated in situ in clusters similar to those obtained after isolation of FDC (Lilet-Leclercq et al., J. Immunol. Meth., 1984, 59, 235).

Cell Survival↗
PubMed1985

5-Nucleotidase activity in isolated follicular dendritic cells.

Follicular dendritic cells isolated from mouse lymph nodes were incubated in the presence of AMP to test 5-nucleotidase (5-Nase) activity. Ultrastructural observations showed the presence of 5-Nase on external membranes but also some activity inside the nucleus. 5-Nase was found associated to Fc receptors labelled with homologous immunoglobulins fixed on colloidal gold particles. Lymphocytes and macrophages, found in association with the follicular dendritic cells, were either 5-Nase positive or negative. The hypothetical roles played by 5-Nase in germinal centers are discussed.

5'-Nucleotidase↗
PubMed1985

Retention of immune complexes by Fc receptors on mouse follicular dendritic cells.

Follicular dendritic cells (FDC) are located inside lymph follicles and are mainly characterized by their capacity to retain antigens. We investigated this aspect in mice lymph nodes by using bovine serum albumin (BSA) labelled with 5-nm colloidal gold particles and homologous anti-BSA antibodies bound to 20-nm gold particles. Gold-labelled BSA injected alone in non-immunized mice was only rarely found in FDC cytoplasmic interdigitations. Injected in the form of immune complexes, it was retained by FDC. Antigen-free anti-BSA antibodies injected under similar conditions as immune complexes were always found in draining lymph nodes in the same locations as BSA-anti-BSA immune complexes. F(ab')2 from mouse immunoglobulins linked to colloidal gold particles were very rarely found between the FDC extensions, whereas it was intensely phagocytosed by macrophages. Our study permitted precise ultrastructural localization between FDC cytoplasmic extensions or inside macrophages and other cells of the lymph nodes, but it also pointed out that homologous antibodies linked to colloidal gold particles might be retained by FDC in the absence of antigens. These observations, carried out with colloidal gold, were checked by using 125I-labelled anti-BSA antibodies. Complement activation determinations of gold-labelled antibodies or immune complexes showed that antibodies or immune complexes fixed on colloidal gold particles do not activate the complement. This observation enabled us to conclude that Fc receptors play a significant part in the retention of gold-labelled antibodies or immune complexes by FDC of lymph nodes.

Animals↗
PubMed1985

Isolation of follicular dendritic cells from human tonsils and adenoids. III. Analysis of their Fc receptors.

Follicular dendritic cells (FDC), isolated from human tonsils or adenoids, were tested for their capacity to retain monomeric, aggregated or antigen-bound human antibodies in the absence of serum. FDC retain fluorescein-labelled heat-aggregated human immunoglobulins, but not monomeric ones nor fluorescein-labelled F(ab')2 in monomeric or aggregated form. Ultrastructural observations showed that colloidal gold-labelled monomeric, or antigen-bound, antibodies directed against tetanus toxoid are retained by dendrites and membrane infoldings of FDC but are never located in cytoplasmic vesicles. This retention was inhibited by incubating FDC with unlabelled aggregated or antigen-bound antibodies. When gold-labelled anti-tetanus toxoid antibodies were incubated in the presence of protein-A before the contact with FDC, a strong reduction of their retention occurred. This further suggested the presence of Fc receptors on isolated tonsillar FDC. Endocytosis was not observed in isolated FDC, even after prolonged incubation in presence of labelled immune complexes: their Fc receptors are, thus, not related to a phagocytic activity as they are in macrophages. Simultaneous ultrastructural labelling of Fc and C3b receptors with colloidal gold particles of different sizes did not reveal any clear relations between these two receptors on the surface of FDC.

Adenoids↗
PubMed1984

Isolation of follicular dendritic cells from human tonsils and adenoids. I. Procedure and morphological characterization.

Follicular dendritic cells have been isolated from human tonsils and adenoids and characterized at the ultrastructural level. Follicles were dissected and digested with different hydrolytic enzymes. The cells were separated by sedimentation at unit gravity. By this procedure we obtained follicular dendritic cells enveloping lymphocytes with their cytoplasmic extensions in a way analogous to that described for isolated thymic nurse cells. The ultrastructural features of isolated follicular dendritic cells are similar to those observed in situ. Prolonged enzymatic action caused loss of the enveloped lymphocytes.

Adenoids↗
PubMed1984

Isolation of follicular dendritic cells from human tonsils and adenoids. II. Immunocytochemical characterization.

Follicular dendritic cells (FDC) are specialized cells found only within lymphoid follicles. They bind immune complexes and play a role in the presentation of antigen to follicular B cells and in the generation of B cell memory. In the present report the isolation of FDC from human tonsils and adenoids is described. These isolated cells have an unusual spherical arrangement and enclose lymphocytes within extensions of their membranes. Their ultrastructural features are similar to those observed in situ. The reactivity of isolated FDC with a number of monoclonal antibodies was analyzed by immunofluorescence and by immunostaining (at the electron microscopic level) with colloidal gold. In keeping with the results of previous investigations on tissue sections IgM, IgG and IgA (but not IgD) can be detected on the surface of isolated FDC, as can C3b receptors and the FDC-associated antigen detected by monoclonal antibody R4/23. The immunoglobulins associated with FDC are mostly embedded in an electron-dense material. The majority of the lymphoid cells enclosed within the membrane extensions of FDC are of B cell type. These results suggest that isolated FDC may be suitable for further in vitro investigation of their role in the humoral immune response.

Adenoids↗
PubMed1984

Functional study of human tonsillar follicular dendritic cells.

Follicular dendritic cells (FDC) isolated from human tonsils and adenoids appear as round clusters where the FDC surround lymphoid cells. Using fluorescein and colloidal gold labelled antibodies we determined their surface antigens, the immunoglobulins they fix and the cells they envelope. Isolated FDC react with specific anti-FDC antibodies but also with an anti-monocyte/macrophage antibody and with anti-HLA-DR antibodies. They retain IgG, IgM, IgA and IgE but not IgD immunoglobulins; this retention occurs, according to our results, via their Fc and C3b receptors. The cells they envelope are mainly B cells, but also occasionally T helper cells. T suppressor cells were only rarely found in contact with FDC. We suggest that FDC create a micro-environment favourable to the proliferation and differentiation of B cells during the humoral response.

Adenoids↗
PubMed1984

Nuclear bodies in mouse lymphoid cells stimulated by lipopolysaccharide.

C57 BL/6J mouse spleen lymphocytes have been stimulated by a polyclonal mitogene, the lipopolysaccharide of E. coli (LPS). Depending on the LPS concentration, two pathways of B lymphocyte differentiation can be obtained. At low dose, the population is mainly composed of blast cells (85%) and at a high dose, the latter transforms into plasma cells (80%). Four types of nuclear bodies have been distinguished and quantitatively studied at several stages of cell differentiation. Only the simple nuclear bodies type A, which could be related to the nuclear matrix, show quantitative modifications in small lymphocytes. Connections between granular nuclear bodies (type D) and nucleolar material have been observed. Some granular nuclear bodies exhibit a morphological zone similar to the nucleolar fibrillar centre as well as fibrillar and granular components. Autoradiographic studies indicate that the granular nuclear bodies contain RNA synthesized elsewhere in the nucleus and that this RNA subsequently migrates to the cytoplasm. Furthermore connections between granular nuclear bodies and chromatin have also been observed.

Animals↗
PubMed1983

Colloidal gold, a useful marker for antigen localization on follicular dendritic cells.

Bovine serum albumin (BSA) bound to colloid gold particles (BSA-gold; 20 nm diameter) and injected into preimmunized mice was found at ultrastructural level in different locations of the lymph nodes. It was detected particularly in the secondary lysosomes of macrophages and between the cytoplasmic processes of the follicular dendritic cells. Between these processes the gold particles were isolated or grouped in clusters; they were in close contact with cell membranes or embedded in dense material. Colloidal gold injected alone was not retained on these cells. The presence of anti-BSA antibodies in the serum was necessary for trapping of BSA-gold particles on follicular dendritic cells. Injections of BSA alone after BSA-gold had been administered to preimmunized mice eliminated most of the BSA-gold from the dendritic processes. BSA-gold is thus trapped in the form of immune complexes which behave characteristically. BSA-gold is thus a suitable marker for antigen localization. Being small and electron dense it permits more precise location than radioactive markers.

Animals↗
PubMed1982

Follicular dendritic cells in lymph nodes after x-irradiation.

Follicular dendritic cells (FDC), non lymphoid cells present in lymph follicles, are characterized by numerous cytoplasmic processes retaining antigen-antibody complexes. Their origin, nature and function are unknown. Mice inguinal lymph nodes after 4.5 or 7.5 Gy X-irradiation were depleted of lymphoid cells. Ultrastructural observations during the first few days post-irradiation show that FDC are unaltered and possess dendritic processes enveloping dense material. Furthermore, they show intense metabolic activity. A lamina densa, never observed so well-developed in other lymph node cells, was detected around the nuclear envelope. The localization of junctions between FDC was analysed. FDC preserve their typical cytoplasmic processes even if lymphoid cells are rare. The latter thus seem not to be responsible for the maintenance of FDC integrity or their development. The possible role of this for antibody production is discussed. Irradiated lymph nodes of lymphoid cells are highly convenient for studying FDC. Isolation of FDC from irradiated lymph organs would seem to be possible.

Animals↗
PubMed1981

Thymic microenvironment and cultures derived from mouse thymic explants. A morphological study.

Cultures derived from thymus fragments of embryonic (18-19 day old), newborn or one month old C57BL mice have been characterized functionally l(phagocytic and nonspecific esterase activities) and morphologically by means of light, scanning (SEM) and transmission (TEM) electron microscopy. The observations show the heterogeneity of the cell populations composing the monolayers. After a few days incubation macrophages appear as the predominating cell type, while epithelial cells usually constitute no more than 30% of the cells. Experiments designed to determine the fate of lymphocytes adhering to the monolayers lead us to believe (on the basis of SEM morphometric analysis) that the survival of lymphocytes attached either to thymic macrophages or to epithelial cells is improved during the first days of coculture. This survival enhancement does not, however, appear to be a specific inductive effect since a similar survival increase is found when lymphocytes adhere to non-thymic cells. In contrast with the monolayer, the explant provides a three-dimensional culture system able to preserve intact thymic microenvironmental conditions since numerous lymphocytes are found even in five week old cultures which were not overlaid with thymocytes or spleen cells.

Animals↗