The recognition of hypothalamo-neurohypophysial functions by developing T cells.

Neuropeptide signals and specific neuropeptide receptors have been described in the thymus supporting the concept of a close dialogue between the neuroendocrine and the immune systems at the level of early T-cell differentiation. In this paper, we review recent data about neurohypophysial (NHP)-related peptides detected in the thymus from different species. We suggest that we are dealing in fact with other member(s) of the NHP hormone family, which seems to exert its activity locally through a novel model of cell-to-cell signaling, that of cryptocrine communication.

Isolation and long-term cultivation of human tonsil follicular dendritic cells.

Highly purified follicular dendritic cells (FDC) were isolated from human tonsils and cultivated for up to 150 days. The cell separation method employed produced pure aggregates (FDC-clusters) composed of FDC and germinal center lymphoid cells, useful for the analysis of the relationship between these two cell types and of the behavior of FDC in culture. During the first few days of culture, lymphoid cells located between FDC extensions survived better than those which were free or partly covered by FDC.

Localization of interleukin 6 mRNA in human tonsils by in situ hybridization.

We have investigated which areas produce interleukin 6 (IL 6) in human tonsils. This growth factor is required for the terminal differentiation of B lymphocytes into plasmocytes. Using 35S-labeled IL 6 cDNA we demonstrated IL 6 gene expression over various areas of the tonsils, with consistent exception of the follicles, by in situ hybridization.

Cytokines produced in lymph follicles.

The events occurring inside lymph follicles during a germinal center reaction are poorly understood. Using B and T lymphoid cell populations prepared from human tonsillar lymph follicles, and enriched or not in macrophages or in follicular dendritic cells, we examined the production of cytokines by these cells in vitro. Interleukin 6 (IL-6) and tumor necrosis factor (TNF) were found in the supernatants of cultures stimulated with phytohemagglutinin or pokeweed mitogen.

Intercellular contacts between germinal center cells. Mechanisms of adhesion between lymphoid cells and follicular dendritic cells.

Intercellular connections exist between germinal center cells especially between lymphoid cells and follicular dendritic cells (FDC). Even after isolation, FDC remain associated to lymphocytes and are able, in a cell suspension, to establish new connections with others. Using human tonsillar cells or mouse lymph node cells we analysed these connections which were shown to be species-specific.

Influence of immunoglobulin isotypes and lymphoid cell phenotype on the transfer of immune complexes to follicular dendritic cells.

Follicular dendritic cells (FDC) are located only inside lymph follicles and are characterized mainly by their capacity to retain high amounts of immune complexes by their Fc or C3b receptors. In this work, we examine the influence of immunoglobulin isotypes and the subset of lymphoid cells (B or T) upon the transfer of immune complexes from lymphocytes to FDC. FDC isolated from mice lymph nodes by enzymatic digestion are able to fix, through Fc receptors, gold-labeled immune complexes presented by lymphoid cells.

Isolation of follicular dendritic cells from human tonsils and adenoids. V. Effect on lymphocyte proliferation and differentiation.

Follicular dendritic cells (FDC) are located only in lymph follicles and are characterized by their capacity to retain high amounts of immune complexes on their plasma membranes. As their functions in germinal centres are unknown, we isolated them from human tonsils and cultured them with autologous lymphoid cells. Cultures of lymphoid cells alone or with added macrophages were used as controls.

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.

Isolation of follicular dendritic cells from human tonsils and adenoids. VI. Analysis of prostaglandin secretion.

Follicular dendritic cells (FDC) are able to fix high amounts of immune complexes by C3b or Fc receptors without endocytosis and for long periods of time. In order to determine the function of this retention, we analysed the secretion of prostaglandin E2 (PGE2) by FDC in vitro; indeed, it is well-known that immune complex fixation on cells may induce PGE2 production. FDC were isolated by enzymic digestion of lymph follicles dissected under the biomicroscope from human tonsils or adenoids.

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.

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.

[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.