The maintenance and regulation of the humoral immune response: persisting antigen and the role of follicular antigen-binding dendritic cells as accessory cells

Follicular dendritic cells in the regulation and maintenance of immune responses

The objectives of this report are to explore known and potential regulatory roles of follicular dendritic cells (FDCs) in immune responses. FDCs are found in B-cell areas of lymphatic tissue and are especially rich around germinal centers where B-cell proliferation is occurring. Recent advances in isolating FDCs in our laboratories made it possible to begin investigating interactions of FDCs with other cells in vitro. In a series of experiments, we sought to determine whether a low concentration of FDC-enriched cells (2-10%) could enhance B-cell and/or T-cell mitogenesis. The results showed that an enriched population of FDCs markedly enhanced lipopolysaccharide-induced stimulation of nude mouse spleen cells, while an equivalent number of resident peritoneal cells or thymocytes had no effect. Depletion of Thy 1.2 positive cells or an exposure to 2400 rads of gamma radiation did not abrogate the enhancing capacity of FDC-enriched cells. FDC-enriched cells also increased phytohemagglutinin-induced proliferation. Scanning electron microscopy of FDC preparations showed that antigen-bearing dendritic processes of Type 2 FDCs have a "beaded" appearance. It was proposed that these immune complex coated microspheres may represent an important mechanism for exposing persisting antigen to the immune system. The gradual shedding of these microspheres may play an important role in regulating and maintaining immune responses within lymphoid tissues.

Spontaneous and egg antigen-induced syntheses of immunoglobulin and antibody by spleen cells and hepatic granulomas of mice infected with Schistosoma japonicum

In the absence of egg antigen (SEA), spleen cells from C57BL/6 mice infected for 22 weeks with Schistosoma japonicum were spontaneously induced in vitro to synthesize total immunoglobulin and antibody to SEA. Hepatic granulomas from mice infected for 12 weeks, but not for 22 weeks, also showed spontaneous syntheses of total immunoglobulin and antibody to SEA, but these syntheses were not enhanced upon the addition of SEA. Total immunoglobulin production was enhanced when SEA was added to spleen cells from mice infected for 4 to 7 weeks but not at any other time point.

An immune response profile model for immunogenicity quantitation

We propose an analytical model, which can simultaneously depict many fundamental characteristics of the immunogenicity of various vaccines. This model, the Immune Response (IR) profile, conveniently expresses the mathematical relation between pre- and post-vaccination titers. A vaccine's IR profile is antigen-specific, dose-dependent and post-vaccination interval-dependent. The maximal capability for serological response to a vaccine can be determined using this model irrespective of the dose administered, the post-vaccination assay interval, or the live or killed state of the vaccine. The IR profile obtained from analysis of booster vaccine responses in a limited number of seropositive study subjects can be used to predict maximal antibody titers which are expected after vaccination and can predict the geometric mean post-vaccination antibody titer of a cohort of subjects undergoing primary immunization. Using this model, it is anticipated that the immunoregulation implied by the IR profile may also prove to be correlated with cellular subpopulations and idiotypic antibody functions. Although derived from influenza vaccines analyses, the model successfully describes immune response characteristics following natural infection with malaria and following diphtheria and rubella vaccine administration.

Interdigitating and dendritic reticulum cells in chronic active hepatitis

An ultrastructural study of the cytology of piecemeal necrosis in 12 liver biopsies from patients with chronic active (aggressive) hepatitis revealed a variety of cell types. This communication deals with two particular cell types, only observed in areas of severe piecemeal necrosis--interdigitating reticulum cells (IDRCs) and dendritic reticulum cells (DRCs). IDRCs are typical components of T-cell regions in lymphoid organs. Cells with the characteristics of IDRCs were found in severe piecemeal necrosis at the periphery of portal tracts and in periportal areas. This suggests that areas of periportal piecemeal necrosis are analogous to the T-cell regions of lymphoid organs during immune reactions. DRCs are typical components of B-cell regions in lymphoid organs. Cells with the characteristics of DRCs were found in the central parts of portal tracts with follicle-like aggregations of lymphocytes, as seen in some cases with pronounced piecemeal necrosis. This finding suggest that follicle-like lymphocytic aggregates in portal tracts are analogous to the B-cell regions of lymphoid organs during immune reactions. A mesenchymal origin of DRCs is suggested. The finding of IDRCs and DRCs in severe piecemeal necrosis emphasizes the fundamental similarity of immune reactions in the liver to those in lymphoid organs. These data are discussed in relation to immunological findings in chronic active hepatitis.

Tissue localization and retention of antigen in relation to the immune response

Antigen persists for months or even years in lymphoid tissues of immune animals and this antigen is believed to participate in the induction and maintenance of B-cell memory as well as in the maintenance of serum antibody levels. In the present report we describe the phenomenon of antigen localization and long-term retention on mouse follicular dendritic cells (FDCs). The antigens used were injected in the hind footpads of immune mice and the popliteal lymph nodes were the lymphoid organs generally studied. In addition to presenting the morphological features of mouse FDCs, we report the results of a study of the mechanism of antigen migration from the site of initial localization in the lymph node subcapsular sinus to the regions of follicular retention in the cortex. The migration was followed by light and electron microscopy. The results support the concepts that immune complexes are trapped in the subcapsular sinus and are transported by a group of nonphagocytic cells to follicular regions. The mechanism of transport may involve either migration of pre-FDCs with a concomitant maturation into FDCs, or cell-to-cell transport utilizing dendritic cell processes and membrane fluidity; or a combination of the two mechanisms may be in operation.

Pathogenesis of mouse scrapie: distribution of agent in the pulp and stroma of infected spleens

Fourteen spleens were collected from mice infected with the 139A strain of scrapie, at a time when the concentration of agent in spleen was at a plateau. Scrapie infectivity was present in both the pulp and stromal fractions, but the concentration in stroma was about 10 times greater than that in pulp. On average, 1000 pulp cells were required to give 1 LD50 unit of scrapie infectivity. Linear regression analysis of data from 64 mouse spleens showed that the total infectivity correlated with tissue weight (P less than 0.001). The titres of the 14 stromal fractions were significantly correlated with whole spleen weight (P less than 0.02) and with the weight of stroma (P less than 0.02), but not with pulp weight. Hence, the titres in the isolated stroma probably reflect those of the stroma in vivo. In contrast, there was no correlation between total pulp titre and spleen weight, pulp weight or pulp cell number. Moreover, gentle washing of pulp cells removed about 80% of the total infectivity. This suggests that much of the pulp titre is adventitiously associated with cells and is in fact agent released from damaged stroma.

Depressed in vitro and in vivo antibody response and adoptive transfer of delayed hypersensitivity to myoglobin with spleen cells of mice chronically infected with Schistosoma japonicum and injected with myoglobin

Spleen cells from C57BL/6J mice infected for 21 weeks with Schistosoma japonicum did not show an in vitro secondary antibody response upon challenge with sperm whale myoglobin. Mice infected for 13 weeks showed almost no in vivo secondary antibody response to this antigen. Spleen cells from mice infected for 12 to 21 weeks did not adoptively transfer delayed hypersensitivity to this antigen.

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.

Accessory and stimulating properties of dendritic cells and macrophages isolated from various rat tissues

Single cell suspensions of rat lymphoid and nonlymphoid tissues were fractionated on discontinuous gradients of bovine serum albumin into high density and low density subfractions. In general, accessory activity required for responses of periodate-treated T lymphocytes was recovered only in a low density population containing a small percent of the total fractionated cells from lymph nodes, spleen, liver, skin, and peritoneal exudates. Further purification always led to an increase of both accessory activity and number of dendritic cells present in nonrosetting and nonadherent populations. After purification, a high recovery of the total accessory activity was found in fractions that contained a high percentage of dendritic cells resulting in a more than 1,000-fold enrichment in accessory activity per cell. No other fraction obtained during the purification contained significant accessory activity. In all cases, macrophage-enriched populations lacked accessory cell activity. With the exception of peritoneal exudate cell preparations, which contained an inhibitory cell, the level of accessory activity in a given population was always found to be a function of the number of dendritic cells present. Dendritic cells from all sources were nonadherent, nonphagocytic, radio- resistant, and nonspecific esterase negative. They expressed Ia antigens and lacked Fc receptors. Both epidermal and lymph node dendritic cells contain Birbeck granules, subcellular structures previously described only for Langerhans cells. Accessory activity requires viable dendritic cells but is unaffected by 1,000 rad of gamma-irradiation. However, ultraviolet irradiation abolished the activity of accessory cells. The cells that responded to periodate were IgG-negative T cells, whereas IgG-positive B cells could not be stimulated under the same conditions. Only periodate-treated T cells and dendritic cells were needed for responses to occur; removal of virtually all macrophages from these purified preparations had no effect. Dendritic cells were also required as stimulators in mixed leukocyte cultures, whereas macrophages, even though Ia positive, were inert.