Rabbit Anti-rat Thymocyte Serum Research Articles

Suppressive Mechanisms of Sairei-to on Mesangial Matrix Expansion in Rat Mesangioproliferative Glomerulonephritis

Background: Sairei-to (TJ-114) is a Japanese herbal medicine of standardized quality, originating from traditional Chinese medicine. In the present in vivo study, we investigated the suppressive effects of TJ-114 and related drugs, Shosaiko-to (TJ-9), and Saiboku-to (TJ-96), on mesangioproliferative glomerulonephritis (MsPGN) in rats. TJ-9 is a basal prescription of TJ-96 and TJ-114. We evaluated the efficacy of these drugs on proteinuria, extracellular matrix (ECM) accumulation, and superoxide dismutase (SOD)-activity. Methods: MsPGN in Wistar rats was induced by intravenous injection of rabbit anti-rat thymocyte serum (ATS). TJ-114, TJ-9, TJ-96 (500 mg/kg/day), or prednisolone (PSL, 2 mg/kg/day) was orally administered to the rats as drinking water from the day of ATS injection (day 0) to day 8, when rats were sacrificed and the kidney specimens were collected. Macrophage infiltration was evaluated by immunostaining for ED-1. ECM was measured by trichrome-staining, and fibronectin immunostaining. Northern blotting was performed to clarify the mRNA expression of cytokines and fibronectin. SOD-activity in the homogenate of renal cortex was also evaluated. Results: The amount of urinary protein was significantly decreased only in the TJ-114-treated group compared with the disease control group (p < 0.05). The number of ED-1-positive cells was significantly decreased in all the treatment groups (p < 0.05, respectively). Decreases in the trichrome-stained area were observed moderately in the TJ-114-treated group (66% of control, p < 0.001) and mildly in the PSL-treated group (76% of control, p < 0.001). The staining area of fibronectin in the glomerulus was significantly decreased in all the treated groups except PSL, and was especially suppressed in the TJ-114-treated group (45% of control, p < 0.001). Transforming growth factor (TGF) and connective tissue growth factor (CTGF) expression significantly decreased in the TJ-114-treated group to the control level (p < 0.05). TGF-β, CTGF, and fibronectin mRNA were upregulated in the disease control group, and TJ-114 suppressed these mRNA expressions in glomeruli. The SOD-activity of renal cortex-homogenate was significantly augmented in all the treated groups except PSL, markedly in the TJ-96- and TJ-114-treated groups. Conclusion: These results suggest that TJ-114 ameliorates ECM accumulation in experimental rat MsPGN, partly suppressing TGF-β and CTGF expression through the recovery of SOD-activity.

Role of mesangial Factor V expression in crescent formation in rat experimental mesangioproliferative glomerulonephritis.

It has been suggested that fibrin deposition participates in the development of crescents in active glomerulonephritis (GN). In human IgA nephropathy, which is a common form of mesangioproliferative GN (MsPGN), crescent formation is occasionally observed in active disease, leading to end-stage renal failure. Factor V is a membrane-bound potent cofactor for the conversion of prothrombin to thrombin by Factor Xa. An in vivo study was conducted to clarify the contribution of local fibrin production to crescent formation in MsPGN through mesangial Factor V expression. Wistar rats were injected intravenously with rabbit anti-rat thymocyte serum. Three days after injection, mesangiolysis with intense mesangial Factor V expression was observed and immunoelectron microscopy revealed fibrin localization in mesangiolytic lesions, which had spread into the glomerular basement membrane adjacent to the destroyed mesangium, accompanied by clots in Bowman's space. Marked glomerular fibrin deposition, together with its deposition in Bowman's space and cellular crescent formation, was noted with mesangial proliferation on day 8. Specific bands for Factor V mRNA were also detected from isolated glomeruli. Fibrin deposition and cellular crescent formation were significantly suppressed by treatment with anti-Factor V antibody. These results suggest that local fibrin production, following mesangial Factor V expression, together with mesangiolysis that spreads to the adjacent glomerular basement membrane, plays a role in crescent formation in MsPGN.

Coagulation in the mesangial area promotes ECM accumulation through factor V expression in MsPGN in rats.

It is well known that tissue factor starts the extrinsic coagulation pathway, which activates factor X to Xa, and factor V is a membrane-bound potent cofactor for the terminating stage of prothrombin activation by factor Xa. In a previous in vitro study, factor V was induced in cultured mesangial cells by inflammatory stimulation and increased expression of factor V promoted fibrin generation on the cultured mesangial cell surface. We report that extracellular matrix (ECM) accumulation is increased in association with coagulation in the mesangial area through factor V expression in mesangioproliferative glomerulonephritis (MsPGN). Wistar rats were intravenously injected with rabbit anti-rat thymocyte serum accompanied with or without simultaneous injection of rabbit anti-factor V antibody. Time course study in immunohistochemistry revealed that factor V expression was prominent on day 3 and fibrin-related antigen (FRA) deposition, then ECM accumulation, followed from day 3 to day 8. Massive fibronectin depositions and transforming growth factor (TGF)-beta expression were also noted in glomeruli from the disease control group, markedly higher than those in the normal group, and these depositions and expressions were significantly decreased in the anti-factor V neutralizing antibody-injected group. Northern blot analysis revealed that factor V mRNA expression was prominent on day 3 and was weak on day 8. Double-labeling experiments revealed the frequent colocalization of alpha-smooth muscle actin with factor V, FRA, and fibronectin in the same mesangial areas of glomeruli. TGF-beta, connective tissue growth factor (CTGF), collagen type IV, and fibronectin mRNA were upregulated in the disease control group, and anti-factor V-neutralizing antibody injection suppressed these mRNA expressions in glomeruli. The present results suggest that ECM components accumulation may progress in accordance with coagulation in the mesangial area through mesangial factor V expression and upregulated expression of TGF-beta and CTGF in MsPGN.

Suppressive Effects of Rosmarinic Acid on Mesangioproliferative Glomerulonephritis in Rats

Background: Rosmarinic acid is known to be a natural phenolic compound widely distributed in Labiatae herbs such as rosemary, sweet basil, and perilla. In the present study, we evaluated the suppressive effects of rosmarinic acid on mesangioproliferative glomerulonephritis in vivo, which was induced by intravenous injection of rabbit anti-rat thymocyte serum (ATS) to rats. Methods: Rosmarinic acid was orally administered to the rats at a dose of 100 mg/kg/day from the day of ATS injection (day 0) to day 8 when rats were sacrificed. The degree of mesangial cell proliferation and matrix accumulation were evaluated by trichrome staining and by immunostaining for proliferating cell nuclear antigen (PCNA), fibronectin, type IV collagen and fibrin. Superoxide dismutase (SOD)-activity in the homogenate of renal cortex was also evaluated. Results: The number of PCNA-positive cells, staining areas of trichrome, fibronectin, collagen IV and fibrin in the glomerulus were significantly decreased, and SOD-activity of renal cortex homogenate was significantly augmented in rosmarinic acid-treated group. Conclusion: Rosmarinic acid would suppress the proliferation of mesangial cells and glomerular matrix expansion in vivo by its fibrinolytic and anti-oxidative activity.

Suppressive effects of Perilla frutescens on mesangioproliferative glomerulonephritis in rats.

Leaves of Perilla frutescens var. crispa DECNE. (perilla, Labiatae) are used as a garnishing vegetable in East Asian countries as well as an herbal medicine prescribed in Kampo medicines such as Saiboku-to. A previous in vitro study revealed that a decoction of perilla leaves inhibits the proliferation of murine-cultured mesangial cells. In the present study, we evaluated the in vivo anti-proliferative effects of a perilla decoction using rat mesangio-proliferative glomerulonephritis induced by an intravenous injection of rabbit anti-rat thymocyte serum (ATS). Leaves of perilla were boiled, and the decoction was orally administered to the rats as drinking water at doses of 100 and 500 mg/kg/d from the day of ATS-injection (day 0) to day 8, when rats were sacrificed. In the histological evaluation, the total number of glomerular cells, proliferating cell nuclear antigen (PCNA) positive cells, and macrophage/monocyte antigen-positive cells in the glomerulus, was significantly decreased in perilla-treated rats. A significantly lower level of proliferation was induced by the serum of the perilla-treated rats than by that of the controls. These results suggest that the perilla decoction suppresses the proliferation of mesangial cells in vivo by an inhibition of the glomerular infiltration of macrophage/monocytes and of the production of circulating growth factors.

Vitamin E treatment of experimental glomerular disease in rats

Kidney mesangial cells (MCs) and vascular smooth muscle cells (VSMCs) are closely related in terms of origin, microscopic anatomy, histochemistry, and contractility. This relationship suggests a similarity between kidney glomerular sclerosis and atherosclerosis. Vitamin E appears beneficial in the prevention and treatment of coronary heart disease and it also inhibits the proliferation of VSMCs in vitro. Thus, we investigated the effect of vitamin E on glomerular sclerosis and MC-proliferative glomerulonephritis (GN) in two rat models of glomerular disease. A remnant kidney rat model accelerated with hyperlipidemia was used to examine progressive glomerular sclerosis leading to chronic renal failure. A rat model of MC-proliferative GN was induced by the intravenous administration of absorbed rabbit anti-rat thymocyte serum (ATS). In the remnant kidney rat model, dietary supplementation with vitamin E (500 IU dl-alpha-tocopheryl acetate/kg) and cholesterol (2%) significantly inhibited glomerular sclerosis and macrophage infiltration in glomeruli relative to controls receiving basal and cholesterol-supplemented diets. In the ATS-induced GN model, glomerular cell proliferation (principally MCs) was lower in rats fed diets supplemented with vitamin E (1000 IU dl-alpha-tocopheryl acetate/kg) compared with controls fed the basal diet only. Although the degree of glomerular macrophage infiltration was similar in both groups, fewer proliferative cell nuclear antigen (PCNA)-positive cells were observed in the vitamin E group, suggesting that MC proliferation was suppressed via the inhibition of intracellular transduction. Supplemental dietary vitamin E suppresses MC proliferation and glomerular sclerosis in models of glomerular disease in rats. This action of vitamin E in experimental nephritis suggests the value of clinical trials testing the potential benefit of vitamin E in chronic GN patients.

Morphologic and functional consequences of immune-mediated mesangiolysis: development of chronic glomerular sclerosis.

The i.v. injection of a rabbit anti-rat thymocyte serum (ATS) induces mesangiolysis in rats, followed by a mesangioproliferative glomerulonephritis (4 to 7 days after antibody). This proliferative lesion disappears 4 to 6 wks after antibody. In order to induce an antibody-mediated sclerotic glomerular disease, uninephrectomized rats received ATS twice at 6-wk interval. At 6 months after the first antibody injection, albuminuria, arterial blood pressure, and inulin clearances were evaluated and renal morphologic studies were performed. At the time of evaluation, mean arterial blood pressure and inulin clearances were not different between animals that received the antibody and uninephrectomized controls. Rats that were injected with antibody, however, had significantly higher albuminuria compared with that of controls. Glomeruli of rats with ATS revealed expansion of the glomerular mesangial matrix and focal sclerosis. A semiquantitative morphologic analysis revealed an increased incidence of glomerular lesions and a higher glomerular damage index in kidneys of nephritic rats. These data demonstrate that the repetitive injection of ATS to unilaterally nephrectomized rats induces a model of chronic glomerular sclerosis.

Complement dependence of antibody-induced mesangial cell injury in the rat.

Intravenous administration of rabbit anti-rat thymocyte serum (ATS) reactive with Thy-1-like antigens present on rat mesangial cells induces almost immediate (1-hr) mesangial cell injury in rats followed by sequential mesangiolytic and mesangial-proliferative/infiltrative lesions. To determine the role of complement in these ATS-induced glomerular lesions, ATS was given to Lewis rats that had been depleted of C3 by cobra venom factor (CVF). CVF treatment prevented the degenerative changes in mesangial cells and accumulation of even the few polymorphonuclear leukocytes (PMN) seen in the glomeruli (2.67 PMN/glomerulus) 1 hr after ATS-treatment in rats not given CVF. In addition, CVF prevented the mesangiolysis and mesangial hypercellularity seen at day 4. Rat C3 and late complement components identified in the mesangial of ATS-treated rats in close association with the deposition of rabbit immunoglobulin G was also absent as a result of CVF treatment. CVF treatment did not affect binding of ATS to glomeruli as studied by immunofluorescence or paired label radioisotope techniques. The depletion of leukocytes and/or PMN by irradiation or treatment with anti-I-MN serum had no effect on the induction of the acute mesangial cell damage or the mesangiolytic lesion. Irradiation did diminish the 4-day proliferative/infiltrative lesion. Complement depletion normalized the ATS-induced increase in mesangial uptake of heat-aggregated human gamma-globulin (655.0 +/- 35.2 micrograms in ATS-treated vs 20.3 +/- 2.9 micrograms/5 X 10(4) glomeruli in ATS plus CVF-treated rats; mean +/- SEM). Small immune deposits present in the mesangial areas of kidneys 4 to 5 days after CVF treatment represented CVF-anti-CVF antibody-C3 complexes. The model of mesangial cell damage induced by ATS in the rat is complement-dependent and may relate, at least in part, to complement-mediated mesangial cell lysis.

The specificity of nephritogenic antibodies. IV. Binding of monoclonal antithymocyte antibodies to rat kidney.

Polyclonal rabbit antirat thymocyte serum (ATS) has been shown to form in situ glomerular immune aggregates following perfusion into normal rat kidney ex vivo. This may be due to the presence of T-cell-like epitopes in the rat kidney, or it may be a result of contaminating anti-connective-tissue antibodies in ATS. To exclude the latter possibility we investigated binding to the rat kidney of three different (mouse) monoclonal antirat thymocyte antibodies (anti-T-cell MoAbs), directed to Thy 1.1 antigen, as well as (control) anti-B-cell MoAbs. The MoAbs were incubated in vitro with kidney sections or perfused into the blood-free rat kidney ex vivo. It was shown using immunofluorescence (IF) and immunoelectron microscopy (IEM) (peroxidase technique) that the anti-T-cell MoAbs used, in contrast to anti-B-cell MoAbs, are able to bind with glomerular capillary walls, and with mesangial structures after incubation in vitro or perfusion ex vivo. Although staining patterns are not completely identical, the reaction product is clearly demonstrated throughout the glomerular basement membrane (GBM) and along the plasma membranes of endothelial and epithelial cells, after contact with either of the three anti-T-cell MoAbs used. It is concluded that the presence of T-cell-like epitopes in the rat kidney may lead to immune complex formation following contact with anti-T-cell MoAbs. The nephritogenicity of rabbit ATS, as well as of some batches of clinically used ATS, may also be explained by this mechanism rather than by the usually assumed presence of contaminating antibodies in these polyclonal antisera.

Immunoelectron microscopic demonstration of Thy-1 antigen on the surfaces of mesangial cells in the rat glomerulus.

Mesangial cells of F344 rats degenerated and then disappeared within 2 days after the intravenous administration of rabbit antirat thymocyte serum (ATS). Rabbit IgG and rat C3 were identified in the mesangium in the rat glomeruli. To establish the glomerular binding site of ATS administered intravenously into rats, one kidney of each rat given ATS intravenously 12 h earlier was perfused ex vivo through the renal artery with peroxidase-labeled antirabbit IgG followed by sequential glutaraldehyde and diaminobenzidine perfusions to minimize the ultrastructural damage. The other kidney was removed before the perfusion for histologic study to examine the glomerular injury. The rabbit IgG identified by peroxidase-reaction product was present diffusely in the glomerular mesangium when viewed by light microscopy and exclusively on the surfaces of most mesangial cells by electron microscopy. Immunofluorescence microscopy showed rabbit IgG essentially in the mesangium, and electron microscopy revealed the degeneration of mesangial cells in the kidneys that had been removed before the surgical perfusion. However, no histological abnormalities were found in the kidneys from control rats given ATS absorbed with rat thymocytes. The present study showed that the intravenous administration of ATS into rats induced the extensive mesangial cell damage by the binding of ATS to Thy-1 antigens on the mesangial cells.

THE SPECIFICITY OF NEPHRITOGENIC ANTIBODIES

Injection of rabbit anti-rat thymocyte serum (ATS) i.v into rats induces a transient glomerulopathy characterized by immune aggregates localized in the mesangium and along the glomerular capillary wall, as detected by immunofluorescence (IF) techniques. Neither light microscopical alterations in the kidney, nor proteinuria could be detected in these animals and no autologous IgG could be observed in the glomeruli during the observation period (45 days). Results from ex vivo perfusion studies showed identical localization of immune aggregates--which, in electron microscopy, appear to be localized subepithelially. The ATS used, was monospecific in that no other specificities could be detected after thorough absorption with rat tissue extracts including tubular brushborder antigens, so it is concluded from these data that ATS is able to participate in the formation of immune complexes in situ by recognizing epitopes both in the mesangium and at the epithelial side of the glomerular basement membrane.

176 - Effect of rabbit anti-rat thymocyte serum (ATS) and alloantiserum on rat mast cells

176 - Effect of rabbit anti-rat thymocyte serum (ATS) and alloantiserum on rat mast cells

Thy-1: a differentiation marker of potential mammary myoepithelial cells in vitro.

The rat mammary cell line Rama 25 [Bennett, D.C., Peachey, L.A., Durbin, H. & Rudland, P.S. (1978) Cell 15, 283--298] differentiates morphologically in vitro from a cuboidal form to a fusiform cell resembling myoepithelial cells. This differentiation occurs in all clonal isolates of the line. By using three different rabbit antisera specific for Thy-1, we have found that antigenic differentiation accompanies morphologic change to the fusiform state. Very few cuboidal cells had Thy-1 detectable on their surfaces in the living state; but after acetone fixation cytoplasmic Thy-1 was detected by immunofluorescence in all cells of the cuboidal type. Thy-1 specificity was established by the fact that immunofluorescence induced by rabbit anti-rat thymocyte serum was abolished by absorption with rat brain but not with erythrocytes, kidney, or liver; immunofluorescence induced by rabbit antiserum to purified Thy-1 glycoproteins from mouse lymphomas was absorbed by Thy-1 positive mouse and rat lymphomas. Surface Thy-1 provides a potentially valuable antigenic marker in the Rama 25 line for studying the differentiation of mammary myoepithelial cells.

Thy-1 antigen expression on rat brain cell lines

Cell lines derived from the central nervous system of rats were screened serologically for the presence of Thy-1 (theta), a cell surface differentiation antigen shared by brain and thymus of rats and mice. Both cytotoxicity absorption and indirect immunofluorescence assays were performed using a rabbit anti-rat thymocyte serum (ATS) with Thy-1 specificity. The complement-dependent cytotoxicity of ATS detected a mouse-rat cross-reacting determinant of the molecule bearing the Thy-1 antigen. Of 20 lines tested, 1 of 6 neuronal and 7 of 14 non-neuronal lines expressed Thy-1, as judged by their capacity to absorb ATS cytotoxicity for a Thy-1 positive thymoma line. Similar results were obtained in quantitative absorption assays of these lines employing a mouse anti-Thy 1.1 alloantiserum, but the xenoantiserum (ATS) was more sensitive for detecting the rat molecule bearing Thy-1. Indirect immunofluorescence, which was performed on several of the lines, yielded results in complete agreement with the cytotoxicity absorption assays, and revealed a generalized distribution of antigen in a speckled or patchy pattern over the membrane of cell bodies and processes.

Bone marrow transplantation in the busulfin-treated rat. III. Relationship between myelosuppression and immunosuppression for conditioning bone marrow recipients.

Lewis rats were given graded doses of cyclophosphamide (CY) alone or in combination with graded doses of busulfan (BU), rabbit anti-rat thymocyte serum, or BU plus rabbit anti-rat thymocyte serum, and transplanted with bone marrow from syngeneic or allogeneic Ag-B-incompatible ACI donors. Another gr

Suppressor cell influence in selected strains of inbred rats: III. Evidence for nonspecific suppression by a lymphocyte-macrophage cooperation

Lewis (LE) and Brown-Norway (BN) rats treated in vivo with rabbit anti rat thymocyte serum demonstrate a reversal in relative responsiveness when assayed to mitogens and antigens via lymphocyte transformation, i.e., the BN rat now responds to a greater magnitude than the LE rats. Spleen cells, from both strains, that have been eluted from glass wool columns, demonstrate elevated responses to mitogens and antigens when compared to unfractionated spleen cells. The responses by these unfractionated and nonadherent populations can 1) be further enhanced subsequent to the treatment with anti-thymocyte serum and 2) suppressed after addition of macrophages from either strain, but especially by BN derived macrophages. The adherent cells from LE spleens respond to the above treatments in a similar fashion as the other populations. The responsiveness of adherent BN cells is only partially restored following treatment with anti-thymocyte serum, and is not further suppressed upon the addition of macrophages. These data are indicative of a lymphocyte-macrophage cooperation in this mechanism of suppression.

BONE MARROW TRANSPLANTATION IN THE BUSULFAN-TREATED RAT

It was previously shown that lethal doses of busulfan (BU) were not immunosuppressive in the rat. In the present studies the effect of rabbit antirat thymocyte serum (RARTS) and cyclophosphamide (CY) as immunosuppressive preparation for marrow allografts in the rat given supralethal doses of BU was investigated. Lewis or LBNF rats were given RARTS for 4-12 consecutive daily doses. They were given a supralethal dose of BU in addition on the last day of RARTS administration. Ag-B-incompatible (ACI). Ag-B-compatible (F344), or syngeneic marrow was infused 24 hr later. In general, RARTS was not toxic to the marrow graft and permitted engraftment of Ag-B-incompatible and compatible marrow. All animals given Ag-B-incompatible marrow and Ag-B-compatible marrow that survived to day 21 were shown to be chimeric, but all those with incompatible marrow subsequently died from severe graft-versus-host disease (GVHD). In other experiments Lewis or LBNF1 rats were given Ag-B-incompatible (ACI) and compatible (F344) marrow after a supralethal dose of BU and single graded doses of CY. Doses of CY as low as 25-50 mg/kg provided sufficient immunosuppression to allow allogeneic engraftment. Transient chimerism was seen up to doses of 100 mg/kg of CY. Permanent chimerism was seen with doses of CY from 150 to 250 mg/kg. The incidence of lethal GVHD increased in parallel with the percentage of animals that were demonstrated to be chimeric. Mild but transient GVHD was seen with Ag-B-compatible marrow given to Lewis rats.

Bone marrow transplantation in the busulfan-treated rat. II. Effect of cyclophosphamide and antithymic serum on the presensitized state.

The purpose of the present study was to develop a model in the busulfan (BU)-treated aplastic rat for investigating sensitization to donor marrow in various donor and recipient combinations differing in their degree of histocompatibility. In addition, cyclophosphamide (CY) and rabbit antirat thymocyte serum (RARTS) were studied as potential agents for reversing the presensitized state. Marrow transplantation was studied in the following donor-host combinations: ACI-Lewis (Ag-B-histoincompatible), F344-Lewis (Ag-B-histocompatible), and F344-LBNF1 ("very histocompatible"). The administration of 10(7) donor-type spleen cells i.v. 9 days before marrow infusion sensitized (prevented marrow takes) in all three systems. BN cells were able to sensitize Lewis recipients to F344 marrow because of minor antigens shared by the BN and F344 rat strains. RARTS given as six consecutive daily doses (1.5 ml each) beginning 1 day after immunization and ending 1 day before marrow grafting failed to abolish the presensitized states in all three systems studied. A single dose of CY (150 mg/kg), given alone or combined with RARTS, was able to reverse the measurable effects of presensitization in the histocompatible and "very histocompatible" situations, but was without effect on the histoincompatible system. The present studies were performed in a limited number of rat strain combinations, and the general and specific effects of CY on presensitization to minor histocompatibility antigens in other situations such as outbred mammalian systems remain to be determined.

Cellular Differentiation in the Thymus

Abstract By immunization of rabbits with rat thymus cells a rabbit anti-rat thymocyte serum (ARTS) was obtained which reacted with thymic and peripheral lymphocytes, as shown by both specific immunofluorescence and cytotoxicity testing. Upon proper absorption or dilution this serum was rendered specific for rat thymocytes but cross-reacted with mouse thymocytes. The antigen which it defined was present in 100% of thymocytes in adult rats of all strains tested and in less than 7% of lymphocytes in adult spleen and lymph nodes. It was represented on three-quarters of the cells in both the thymus and spleen of the fetal rat but approached the adult distribution before the age of 4 weeks. ARTS also contained antibodies reactive with a second antigen present to an equal extent on both thymocytes and peripheral lymphocytes. Both antigens appeared to be distinct from that defined by the natural antibody in normal rabbit serum. It was suggested that the immunosuppressive effect of long term treatment with anti-thymocyte sera may depend in part on destruction of newly generated cells entering the peripheral pool from the thymus and bearing the thymus-specific antigen.

The effect of heterologous anti-lymphocytic serum on the small lymphocyte population of rats.

Treatment of Lewis strain rats with a single subcutaneous dose of rabbit anti-rat thymocyte serum (RARTS) resulted in a marked depletion of small lymphocytes in the blood and thoracic duct lymph for approximately 10 days. While the thoracic duct lymphocytes were declining in numbers, rabbit antibody could be detected on the surfaces of a high percentage of the lymph cells. Furthermore, the thoracic duct lymphocytes were unable to initiate graft vs. host reactions during the period of depletion, even when injected in extremely large doses. Approximately 2 wk after treatment, the numbers and immune competence of the small lymphocytes returned to normal.