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Ralf Stahlmann - One of the best experts on this subject based on the ideXlab platform.

  • 2 3 7 8 tetrachlorodibenzo p dioxin does not influence the cell proliferation in Popliteal Lymph Nodes after foot pad injection of cellular and non cellular antigens in mice
    Chemosphere, 1992
    Co-Authors: Andrej Schmidt, Hansjurgen Stroh, Maria Korte, Ralf Stahlmann
    Abstract:

    Abstract Several agents (poke weed mitogen, streptozotocin, erythrocytes, etc.) were used to stimulate the cell proliferation in the Popliteal Lymph Nodes by foot pad injection in NMRI mice. One week before the antigen was injected the mice were treated with a single s.c.-injection of 100 ng TCDD/kg body wt or with the vehicle only (toluene/DMSO, 1 + 2, 1.0 ml/kg body wt). One week after the injection of the stimulant the cell number of the Lymph node (LN) was determined with a cell counter after mechanical disintegration in 0.5 ml phosphate buffered saline (PBS). Since no significant effect of TCDD on the proliferation rate of the Lymph node cells was observed, we conducted a further experiment with a higher dose of TCDD using the most effective stimulant only. One week after a single s.c.-injection of 3 μg 14C-TCDD/kg body wt the test was performed with streptozotocin as stimulant. After foot pad injection of streptozotocin the following cell numbers/x 103 μl (mean ± SD) were counted in the cell suspension of the right Lymph node in otherwise untreated mice: 18.4 ± 12.3, after injection of the vehicle (DMSO): 17.3 ± 8.9, and after 1 × 3 μg TCDD/kg body wt: 19.4 ± 12.7. [Positive controls: 4 × 75 mg cyclosporine A/kg body wt: 3.0 ± 1.4 and 4 × 100 mg cyclophosphamide/kg body wt: 4.6 ± 2.6]. The TCDD concentrations in liver, fat and thymus were: 0.55 ± 0.58, 1.09 ± 0.73, and 0.27 ± 0.16 ng/g tissue, respectively. We conclude that - in contrast to well-known immunosuppressants - TCDD, even at high doses, does not significantly inhibit the proliferation of cells in Lymph Nodes of mice after local stimulation.

  • effects of 2 3 7 8 tetrachlorodibenzo p dioxin on liver thymus and cell proliferation in Popliteal Lymph Nodes after foot pad injection of streptozotocin in rats
    Chemosphere, 1992
    Co-Authors: Hansjurgen Stroh, Andrej Schmidt, Maria Korte, Ralf Stahlmann
    Abstract:

    Immunosuppressive substances can reduce the cell proliferation in the Popliteal Lymph node of rats induced by foot pad injection of, e.g., streptozotocin. We investigated the effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in such an experimental set-up. One week before streptozotocin was injected into the right foot pad (5 mg/40 μl) the rats were treated with a single s.c.-injection of 3 μg 14C-TCDD/kg body wt or with the vehicle only (toluene/DMSO). One week after the injection of streptozotocin the weight of the right and left Lymph Nodes as well as the cell number of both Lymph Nodes were determined after disintegration in phosphate buffered salien. The quotients of the results obtained from the right and the left Lymph node (“index”) were calculated. Relevant organs were weighed and the TCDD concentrations in liver, fat and thymus were measured by scintillation counting. Using cyclophosphamide or cyclosporine A as “positive control” we found a clear-cut reduction of the cell index to values less than 10% of the vehicle controls. Systemic treatment with TCCD, however, at a dose which caused an increase in liver weight and a decrease in thymus weight, did not influence the increase of cells in the Popliteal Lymph node in rats induced by foot pad injection of steptozotocin.

  • Polyhalogenated dibenzo-p-dioxins and dibenzofurans and the immune system. 3. No immunosuppressive effect of 2,3,7,8-TCDD in the Popliteal Lymph node assay (PLNA) in rats.
    Archives of Toxicology, 1991
    Co-Authors: Maria Korte, Ralf Stahlmann, Malgorzata Kubicka-muranyi, Ernst Gleichmann, Diether Neubert
    Abstract:

    We used a modified version of the Popliteal Lymph node assay in rats to investigate the immunosuppressive potential of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). In 10 months we conducted 3 experimental series. Animals were treated with single s.c. injections of TCDD and 7 days later human red blood cells (HRBC) were injected s.c. into the right hind footpad of the rat. Another 7 days later, both Popliteal Lymph Nodes were prepared, weighed, the cell number was counted and the quotients ("index") of these variables from the treated and the untreated side were determined. The doses applied in three experimental series were 600', 60, 6, 0.6, and 0.06 ng TCDD/kg body wt. In the first experimental series only the three highest doses were tested, in a second experimental series doses of 60, 6, 0.6, 0.006 ng TCDD/kg body wt were applied. Combining the results of these two experimental series, a statistically significant difference was found in the cell number index between the controls and the two highest doses tested (60 and 600 ng/kg body wt; p less than 0.01). This result was recently published as an abstract (Korte et al. 1990). However, with slight methodological changes in the third series of experiments (doses applied: 600, 60, 6, 0.6, and 0.06 ng TCDD/kg body wt) and using a greater number of animals we could not confirm these preliminary results. No difference was seen in the immune response to the antigen challenge in controls and in any of the treatment groups. We conclude that TCDD does not clearly influence the immune response as observed in the Popliteal Lymph node assay under our experimental conditions.

Hansjurgen Stroh - One of the best experts on this subject based on the ideXlab platform.

  • 2 3 7 8 tetrachlorodibenzo p dioxin does not influence the cell proliferation in Popliteal Lymph Nodes after foot pad injection of cellular and non cellular antigens in mice
    Chemosphere, 1992
    Co-Authors: Andrej Schmidt, Hansjurgen Stroh, Maria Korte, Ralf Stahlmann
    Abstract:

    Abstract Several agents (poke weed mitogen, streptozotocin, erythrocytes, etc.) were used to stimulate the cell proliferation in the Popliteal Lymph Nodes by foot pad injection in NMRI mice. One week before the antigen was injected the mice were treated with a single s.c.-injection of 100 ng TCDD/kg body wt or with the vehicle only (toluene/DMSO, 1 + 2, 1.0 ml/kg body wt). One week after the injection of the stimulant the cell number of the Lymph node (LN) was determined with a cell counter after mechanical disintegration in 0.5 ml phosphate buffered saline (PBS). Since no significant effect of TCDD on the proliferation rate of the Lymph node cells was observed, we conducted a further experiment with a higher dose of TCDD using the most effective stimulant only. One week after a single s.c.-injection of 3 μg 14C-TCDD/kg body wt the test was performed with streptozotocin as stimulant. After foot pad injection of streptozotocin the following cell numbers/x 103 μl (mean ± SD) were counted in the cell suspension of the right Lymph node in otherwise untreated mice: 18.4 ± 12.3, after injection of the vehicle (DMSO): 17.3 ± 8.9, and after 1 × 3 μg TCDD/kg body wt: 19.4 ± 12.7. [Positive controls: 4 × 75 mg cyclosporine A/kg body wt: 3.0 ± 1.4 and 4 × 100 mg cyclophosphamide/kg body wt: 4.6 ± 2.6]. The TCDD concentrations in liver, fat and thymus were: 0.55 ± 0.58, 1.09 ± 0.73, and 0.27 ± 0.16 ng/g tissue, respectively. We conclude that - in contrast to well-known immunosuppressants - TCDD, even at high doses, does not significantly inhibit the proliferation of cells in Lymph Nodes of mice after local stimulation.

  • effects of 2 3 7 8 tetrachlorodibenzo p dioxin on liver thymus and cell proliferation in Popliteal Lymph Nodes after foot pad injection of streptozotocin in rats
    Chemosphere, 1992
    Co-Authors: Hansjurgen Stroh, Andrej Schmidt, Maria Korte, Ralf Stahlmann
    Abstract:

    Immunosuppressive substances can reduce the cell proliferation in the Popliteal Lymph node of rats induced by foot pad injection of, e.g., streptozotocin. We investigated the effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in such an experimental set-up. One week before streptozotocin was injected into the right foot pad (5 mg/40 μl) the rats were treated with a single s.c.-injection of 3 μg 14C-TCDD/kg body wt or with the vehicle only (toluene/DMSO). One week after the injection of streptozotocin the weight of the right and left Lymph Nodes as well as the cell number of both Lymph Nodes were determined after disintegration in phosphate buffered salien. The quotients of the results obtained from the right and the left Lymph node (“index”) were calculated. Relevant organs were weighed and the TCDD concentrations in liver, fat and thymus were measured by scintillation counting. Using cyclophosphamide or cyclosporine A as “positive control” we found a clear-cut reduction of the cell index to values less than 10% of the vehicle controls. Systemic treatment with TCCD, however, at a dose which caused an increase in liver weight and a decrease in thymus weight, did not influence the increase of cells in the Popliteal Lymph node in rats induced by foot pad injection of steptozotocin.

Maria Korte - One of the best experts on this subject based on the ideXlab platform.

  • 2 3 7 8 tetrachlorodibenzo p dioxin does not influence the cell proliferation in Popliteal Lymph Nodes after foot pad injection of cellular and non cellular antigens in mice
    Chemosphere, 1992
    Co-Authors: Andrej Schmidt, Hansjurgen Stroh, Maria Korte, Ralf Stahlmann
    Abstract:

    Abstract Several agents (poke weed mitogen, streptozotocin, erythrocytes, etc.) were used to stimulate the cell proliferation in the Popliteal Lymph Nodes by foot pad injection in NMRI mice. One week before the antigen was injected the mice were treated with a single s.c.-injection of 100 ng TCDD/kg body wt or with the vehicle only (toluene/DMSO, 1 + 2, 1.0 ml/kg body wt). One week after the injection of the stimulant the cell number of the Lymph node (LN) was determined with a cell counter after mechanical disintegration in 0.5 ml phosphate buffered saline (PBS). Since no significant effect of TCDD on the proliferation rate of the Lymph node cells was observed, we conducted a further experiment with a higher dose of TCDD using the most effective stimulant only. One week after a single s.c.-injection of 3 μg 14C-TCDD/kg body wt the test was performed with streptozotocin as stimulant. After foot pad injection of streptozotocin the following cell numbers/x 103 μl (mean ± SD) were counted in the cell suspension of the right Lymph node in otherwise untreated mice: 18.4 ± 12.3, after injection of the vehicle (DMSO): 17.3 ± 8.9, and after 1 × 3 μg TCDD/kg body wt: 19.4 ± 12.7. [Positive controls: 4 × 75 mg cyclosporine A/kg body wt: 3.0 ± 1.4 and 4 × 100 mg cyclophosphamide/kg body wt: 4.6 ± 2.6]. The TCDD concentrations in liver, fat and thymus were: 0.55 ± 0.58, 1.09 ± 0.73, and 0.27 ± 0.16 ng/g tissue, respectively. We conclude that - in contrast to well-known immunosuppressants - TCDD, even at high doses, does not significantly inhibit the proliferation of cells in Lymph Nodes of mice after local stimulation.

  • effects of 2 3 7 8 tetrachlorodibenzo p dioxin on liver thymus and cell proliferation in Popliteal Lymph Nodes after foot pad injection of streptozotocin in rats
    Chemosphere, 1992
    Co-Authors: Hansjurgen Stroh, Andrej Schmidt, Maria Korte, Ralf Stahlmann
    Abstract:

    Immunosuppressive substances can reduce the cell proliferation in the Popliteal Lymph node of rats induced by foot pad injection of, e.g., streptozotocin. We investigated the effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in such an experimental set-up. One week before streptozotocin was injected into the right foot pad (5 mg/40 μl) the rats were treated with a single s.c.-injection of 3 μg 14C-TCDD/kg body wt or with the vehicle only (toluene/DMSO). One week after the injection of streptozotocin the weight of the right and left Lymph Nodes as well as the cell number of both Lymph Nodes were determined after disintegration in phosphate buffered salien. The quotients of the results obtained from the right and the left Lymph node (“index”) were calculated. Relevant organs were weighed and the TCDD concentrations in liver, fat and thymus were measured by scintillation counting. Using cyclophosphamide or cyclosporine A as “positive control” we found a clear-cut reduction of the cell index to values less than 10% of the vehicle controls. Systemic treatment with TCCD, however, at a dose which caused an increase in liver weight and a decrease in thymus weight, did not influence the increase of cells in the Popliteal Lymph node in rats induced by foot pad injection of steptozotocin.

  • Polyhalogenated dibenzo-p-dioxins and dibenzofurans and the immune system. 3. No immunosuppressive effect of 2,3,7,8-TCDD in the Popliteal Lymph node assay (PLNA) in rats.
    Archives of Toxicology, 1991
    Co-Authors: Maria Korte, Ralf Stahlmann, Malgorzata Kubicka-muranyi, Ernst Gleichmann, Diether Neubert
    Abstract:

    We used a modified version of the Popliteal Lymph node assay in rats to investigate the immunosuppressive potential of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). In 10 months we conducted 3 experimental series. Animals were treated with single s.c. injections of TCDD and 7 days later human red blood cells (HRBC) were injected s.c. into the right hind footpad of the rat. Another 7 days later, both Popliteal Lymph Nodes were prepared, weighed, the cell number was counted and the quotients ("index") of these variables from the treated and the untreated side were determined. The doses applied in three experimental series were 600', 60, 6, 0.6, and 0.06 ng TCDD/kg body wt. In the first experimental series only the three highest doses were tested, in a second experimental series doses of 60, 6, 0.6, 0.006 ng TCDD/kg body wt were applied. Combining the results of these two experimental series, a statistically significant difference was found in the cell number index between the controls and the two highest doses tested (60 and 600 ng/kg body wt; p less than 0.01). This result was recently published as an abstract (Korte et al. 1990). However, with slight methodological changes in the third series of experiments (doses applied: 600, 60, 6, 0.6, and 0.06 ng TCDD/kg body wt) and using a greater number of animals we could not confirm these preliminary results. No difference was seen in the immune response to the antigen challenge in controls and in any of the treatment groups. We conclude that TCDD does not clearly influence the immune response as observed in the Popliteal Lymph node assay under our experimental conditions.

Andrej Schmidt - One of the best experts on this subject based on the ideXlab platform.

  • 2 3 7 8 tetrachlorodibenzo p dioxin does not influence the cell proliferation in Popliteal Lymph Nodes after foot pad injection of cellular and non cellular antigens in mice
    Chemosphere, 1992
    Co-Authors: Andrej Schmidt, Hansjurgen Stroh, Maria Korte, Ralf Stahlmann
    Abstract:

    Abstract Several agents (poke weed mitogen, streptozotocin, erythrocytes, etc.) were used to stimulate the cell proliferation in the Popliteal Lymph Nodes by foot pad injection in NMRI mice. One week before the antigen was injected the mice were treated with a single s.c.-injection of 100 ng TCDD/kg body wt or with the vehicle only (toluene/DMSO, 1 + 2, 1.0 ml/kg body wt). One week after the injection of the stimulant the cell number of the Lymph node (LN) was determined with a cell counter after mechanical disintegration in 0.5 ml phosphate buffered saline (PBS). Since no significant effect of TCDD on the proliferation rate of the Lymph node cells was observed, we conducted a further experiment with a higher dose of TCDD using the most effective stimulant only. One week after a single s.c.-injection of 3 μg 14C-TCDD/kg body wt the test was performed with streptozotocin as stimulant. After foot pad injection of streptozotocin the following cell numbers/x 103 μl (mean ± SD) were counted in the cell suspension of the right Lymph node in otherwise untreated mice: 18.4 ± 12.3, after injection of the vehicle (DMSO): 17.3 ± 8.9, and after 1 × 3 μg TCDD/kg body wt: 19.4 ± 12.7. [Positive controls: 4 × 75 mg cyclosporine A/kg body wt: 3.0 ± 1.4 and 4 × 100 mg cyclophosphamide/kg body wt: 4.6 ± 2.6]. The TCDD concentrations in liver, fat and thymus were: 0.55 ± 0.58, 1.09 ± 0.73, and 0.27 ± 0.16 ng/g tissue, respectively. We conclude that - in contrast to well-known immunosuppressants - TCDD, even at high doses, does not significantly inhibit the proliferation of cells in Lymph Nodes of mice after local stimulation.

  • effects of 2 3 7 8 tetrachlorodibenzo p dioxin on liver thymus and cell proliferation in Popliteal Lymph Nodes after foot pad injection of streptozotocin in rats
    Chemosphere, 1992
    Co-Authors: Hansjurgen Stroh, Andrej Schmidt, Maria Korte, Ralf Stahlmann
    Abstract:

    Immunosuppressive substances can reduce the cell proliferation in the Popliteal Lymph node of rats induced by foot pad injection of, e.g., streptozotocin. We investigated the effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in such an experimental set-up. One week before streptozotocin was injected into the right foot pad (5 mg/40 μl) the rats were treated with a single s.c.-injection of 3 μg 14C-TCDD/kg body wt or with the vehicle only (toluene/DMSO). One week after the injection of streptozotocin the weight of the right and left Lymph Nodes as well as the cell number of both Lymph Nodes were determined after disintegration in phosphate buffered salien. The quotients of the results obtained from the right and the left Lymph node (“index”) were calculated. Relevant organs were weighed and the TCDD concentrations in liver, fat and thymus were measured by scintillation counting. Using cyclophosphamide or cyclosporine A as “positive control” we found a clear-cut reduction of the cell index to values less than 10% of the vehicle controls. Systemic treatment with TCCD, however, at a dose which caused an increase in liver weight and a decrease in thymus weight, did not influence the increase of cells in the Popliteal Lymph node in rats induced by foot pad injection of steptozotocin.

Hajime Hoshi - One of the best experts on this subject based on the ideXlab platform.

  • development of immune complex trapping experimental study of Lymphoid follicles and germinal centers newly induced by exogenous stimulants in mouse Popliteal Lymph Nodes
    Histology and Histopathology, 1999
    Co-Authors: Hajime Hoshi, K Horie, Dong Chen
    Abstract:

    The development of immune complex trapping in newly-induced Lymphoid follicles of draining Popliteal Lymph Nodes was investigated in young adult mice, which had been given bilateral injection of hemocyanin (KLH) or phytohemagglutinin (PHA), each absorbed onto alumina. HRP-anti-HRP immune complex was injected into the footpad 1 day before sacrifice. Using three series of semi-serial cryostat sections prepared from each Popliteal node, the number of Lymphoid follicles in each node was counted, and follicular localization of the in vivo injected and in vitro applied immune complexes in each follicle was determined. By day 5, a large germinal center had developed within each preexisting follicle. A large number of 'new' secondary follicles, each containing a small PNA-positive germinal center, appeared outside pre-existing follicles, from day 5 through day 11 in KLH-treated Nodes, and from day 7 through day 14 in PHA-treated Nodes. Shortly after their appearance, new secondary follicles showed no in vitro or in vivo trapping, but subsequently, many of the new follicles began to display in vitro trapping, at first weakly but later intensely. Occurrence of in vivo trapping in new follicles took some time and was first recognized when new follicles showed intense in vitro trapping. At day 21 or 25, many of the new follicles showed both in vitro and in vivo trapping. It was concluded that in Lymph Nodes treated with a stimulant, secondary follicles containing germinal centers can be formed de novo in the extrafollicular zone where the follicular trapping microenvironment is absent, but subsequently the microenvironment capable of trapping immune complexes develops at the site of formation of new follicles.

  • Morphological Changes in the Mouse Popliteal Lymph Node after Local Injection of Dextran Sulfate
    Tohoku Journal of Experimental Medicine, 1994
    Co-Authors: Horie K, Hajime Hoshi, Kastumi Hamano, Tadashi Kaneko
    Abstract:

    HORIE, K., HOSHI, H., HAMANO, K. and KANEKO, T. Morphological Changes in the Mouse Popliteal Lymph Node after Local Injection of Dextran Sulfate. Tohoku J. Exp. Med., 1994, 172 (3), 175-193-Dextran sulfate 500 (DS) is known to be a potent B-cell mitogen. Injection of this compound (500μg) into the footpads of mice produced characteristic changes in the draining Popliteal Lymph Nodes, including elimination of macrophages from the Lymphatic sinuses and lining the subcapsular sinus, a marked blast reaction throughout the nodal parenchyma, damage to the stroma of the outer peripheral cortex, and disorganization of all the existing primary and secondary Lymph follicles. On day 6 after DS treatment, small Lymphocytes bearing surface Ig were detected and distributed loosely and broadly in the deeper part of the peripheral cortex without any tendency to reorganize Lymph follicles. On day 21, these small Lymphocytes populated the outer and deeper layer of the peripheral cortex, sometimes forming nodular accumulations representing regenerating Lymph follicles, and on day 35, various numbers of regenerated Lymph follicles were present in the peripheral cortex. Tracer studies using FITC-conjugated human serum albumin showed that intraparenchymal diffusion of labeled HSA was highly blocked at the outer peripheral cortex on days 4 through 14, and that this pathway began to reopen at around 21 days. Disorganization of Lymph follicles could be considered due to extensive damage to follicle stromata which became unable to bind B Lymphocytes, and follicles seem to be re-organized in response to Lymph-carried antigen in addition to restored follicle stromata and repopulating B Lymphocytes. Macrophages had little effect on the Lymph follicle formation in this study.

  • further histological observations on Popliteal Lymph Nodes after interruption of the afferent Lymphatic vessels
    Histology and Histopathology, 1993
    Co-Authors: Hajime Hoshi, K Horie, Hidetsugu Nagata, R Takemoto, Gen Murakami, S Suzuki
    Abstract:

    Lymphatic vessels afferent to the Popliteal Nodes in young adult rats and guinea pigs were interrupted at the lowest edge of the Popliteal fossa, and regressive changes in the Nodes occurring 4 to 16 or 18 weeks after surgery were re-examined histologically. In the rat, some Popliteal Nodes were drained by Lymphatic channel(s) from the tail. After surgery, the Popliteal Nodes without Lymphatic channel(s) from the tail underwent regression of all their constituent deep cortical units and also the peripheral cortex comprising Lymph follicles, until at 18 weeks, the Lymphoid organization of the node reached a minimal level. On the other hand, in Popliteal Nodes having a Lymphatic channel from the tail, some deep cortical units and the overlying peripheral cortex underwent hypotrophy, leaving the remaining units and their overlying peripheral cortex little affected. In the guinea pig, the treated Nodes underwent progressive atrophy and ultimately became rudimentary, or even vanished, after 16 weeks. Treated rudimentary Nodes were composed largely of stromal cells only, and these were replaced to a various extent by fat. The present results are discussed in relation to complete and incomplete inhibition of the afferent Lymph flowing into the surgically treated Nodes.

  • Lymph follicles and germinal centers in Popliteal Lymph Nodes and other Lymphoid tissues of germ free and conventional rats
    Tohoku Journal of Experimental Medicine, 1992
    Co-Authors: Hajime Hoshi, Hiroshi Aijima, K Horie, Hidetsugu Nagata, Toru Kaneko, Tadao Ikeda
    Abstract:

    HOSHI, H., AIJIMA, H., HORIE, K., NAGATA, H., KANEKO, T. and IKEDA, T. Lymph Follicles and Germinal Centers in Popliteal Lymph Nodes and Other Lymphoid Tissues of Germ-Free and Conventional Rats. Tohoku J. Exp. Med., 1992, 166 (3), 297-307 - A study was conducted to evaluate the influence of natural exogenous antigen stimulation on the development of Lymph follicles in the peripheral Lymphoid organs of the rat. The number of Lymph follicles and germinal centers per Popliteal node as well as the morphological features of Popliteal Nodes, mesenteric Nodes and Peyer's patches were compared between 8-week-old male Sprague-Dawley rats reared in germ-free, specific pathogen-free (SPF) and conventional environments. In mesenteric Nodes and Peyer's patches from conventional and SPF rats, almost every follicle contained a germinal center. In the mesenteric Nodes from germ-free rats, only 9 of 195 Lymph follicles examined contained a germinal center, but interestingly, in Peyer's patches all the Lymph follicles examined showed a fairly well developed germinal center. The Popliteal Nodes from germ-free rats had no germinal centers and each node contained about 80 Lymph follicles. In six conventional rats and two of five SPF rats used, the number of Lymph follicles per Popliteal node usually ranged from 100 to 130, and some Lymph follicles contained a germinal center. However, in the other three SPF rats the Popliteal node on both sides showed no germinal center, and each contained almost the same number of Lymph follicles as the Popliteal Nodes of other SPF and conventional rats. The present results are consistent with the view that even in the absence of exogenous antigen stimulation, a regional Lymph node of the germ-free rat develops a substantial number of primary Lymph follicles by way of a non-immunological cellular activity, and that natural exogenous antigens may influence the development of Lymph follicles by stimulating the cellular activity rather than evoking the humoral immune responses.