Oligocellular mechanism in the production of antibodies: in vitro response to a haptenic determinant

Spleen explants from mice tolerant to rabbit serum albumin (RSA) failed to react in vitro to dinitrophenyl (DNP)-RSA; antibodies to DNP were, however, produced by such spleens, when stimulated with α-DNP-poly(Lys). To study the function of T and B cells in recognition of carrier determinants, spleen explants from X-irradiated mice, which had been inoculated with combinations of thymus and bone marrow cells from normal and from RSA tolerant donors, were tested for their reactivity in vitro to the DNP-RSA conjugate. A significant response was obtained only by spleens of mice containing bone marrow and thymus from normal donors. Spleens of mice treated with thymus from tolerant and bone marrow from normal or with thymus from normal and bone marrow from tolerant donors did not respond to DNP-RSA. The absence of the response to DNP-RSA by tolerant B cells combined with normal T cells was unexpected. It could not be attributed to binding of the tolerogen to B cells which would have prevented the interaction with T-cells. Neither could the result be attributed to an inhibition of normal cells by RSA-tolerant B-cells. θ-positive cells in the bone marrow are not the cells controlling the recognition of carrier determinants in the B population, since elimination of θ-positive cells did not affect the reactivity of spleens repopulated with B and T cells. Nor are bone marrow macrophages responsible for the lack of reactivity in spleens containing tolerant B cells, since normal macrophages did not restore reactivity. Hence, the production of antibodies to DNP is based on the recognition of carrier determinants not only by T cells, as previously established, but also by B cells. Whether this indicates a B-B in addition to the T-B cell cooperation is an inviting possibility.     

Thymus dependency of cells involved in transfer of delayed hypersensitivity to listeria monocytogenes in mice

Delayed-type hypersensitivity (DH) to Listeria antigens was induced in inbred C3Hf/Umc mice by intravenous injection of a sublethal dose of viable Listeria monocytogenes. Bone marrow, spleen, and lymph node cells from the immune mice were capable of passive transfer of DH to syngeneic neonatally thymectomized or lethally (900 R) irradiated recipients. Immune thymus cells as well as immune serum were ineffective in transferring DH to irradiated animals. In vitro treatment with antitheta isoantibody (anti-θ) and complement abolished the capacity of spleen and bone marrow cells from immune donors to transfer DH to irradiated hosts, indicating the thymus dependency of this cell population. The results with bone marrow indicate the existence of a small, but biologically significant, thymus-dependent population in this tissue.     

Studies of delayed hypersensitivity to L. Monocytogenes in mice: nature of cells involved in passive transfers

C3Hf/Umc mice were immunized by an intravenous injection of a sublethal dose of live Listeria monocytogenes. The animals developed delayed-type hypersensitivity (DH) concomitant with infectious immunity to this organism. Delayed hypersensitivity could be transferred to normal lethally irradiated mice with spleen cells from immune animals. The immune cells cells responsible for transfer of adoptive immunity were susceptible to in vitro cytolytic action of anti-theta iso-antibody and complement, since such treatment rendered these cells incapable of further passive transfer of specific immunity to Listeria. The acquired DH to Listeria persisted in mice after 900 R lethal irradiation, provided normal syngeneic bone marrow cells were also administered, thus indicating the persistance of a cell population in the immune irradiated mice, resistant to effects of radiation. The radio resistant nature of this immune cell population was further demonstrated by passive transfer with spleen cells, derived from preimmunized lethally irradiated mice to normal syngeneic mice or to lethally irradiated nonimmunized hosts reconstituted with normal bone marrow which then responded to antigenic challenge with DH.Treatment of the immune radio resistant spleen cells in vitro with anti-theta and complement eliminated passive transfers of DH by these cells; however, this effect was less obvious than similar treatment of the immune, nonirradiated, spleen cells.     

Papers to appear in forthcoming issues

Tolerance to the TNP haptenic determinant was induced by a single intravenous injection of trinitrophenylated syngeneic cells. Syngeneic spleen or thymus cells were capable of acting as carriers for tolerance induction while syngeneic bone marrow cells were not. Syngeneic spleen cells depleted of θ-positive and adherent cells were also suitable carriers for tolerance induction. Sonicated haptenated spleen cells, but not sonicated haptenated bone marrow cells induced tolerance. The ability of haptenated cells to induce tolerance was not correlated with their localization in lymphoid organs. Furthermore, cells recovered from the spleens of lethally irradiated animals reconstituted with bone marrow cells 1 week previously were incapable of inducing tolerance after hapten-modification. However, after 3 weeks, spleen cells from bone marrow-reconstituted mice had acquired the ability to induce tolerance. These results suggest that only certain types of syngeneic cells have the ability to act as carriers for tolerance induction; merely being syngeneic, and therefore presumably nonimmunogenic, is not sufficient to permit the cell to act as a carrier for tolerance induction.     

Thymus cell traffic induced by antigen stimulation

Spleens of adult mice immunized with either RSA or RGG responded in vitro to DNP-RSA or DNP-RGG, respectively, at a significantly higher rate than spleens of untreated mice. Stimulation in vitro could be achieved by short pulses of the antigen (5–15 min). It was found that thymectomy prior to injection of the carrier protein interfered with the subsequent response in vitro to the hapten-carrier conjugate, and that this was much more pronounced in 8- to 10-day-old mice than in older mice. It is suggested that antigen stimulation in vivo triggers thymus cell migration. Although this is by no means the only mechanism accountable for manifestation of the carrier effect, it may represent a device for amplification of the immune response in vivo.     

Nature of T-cells resident in spleens of thymectomized,lethally irradiated,bone marrow-reconstituted mice

Adult thymectomized, lethally irradiated, bone marrow-reconstituted (ATxXB) mice that had been weakly primed with SRBC or HRBC between thymectomy and irradiation were shown to retain antigen-specific immunological memories for at least 1–5 months after bone marrow reconstitution. This could be shown by anamnestic antibody response in vivo as well as by proliferative response of the spleen cells to the test antigens in vitro. Spleen cells taken from ATxXB mice showed a reduced but significant proliferative response to nonspecific T-cell mitogens, in particular to Con A, in vitro. Treatment of the donor bone marrow cells used for reconstitution of ATxXB mice with anti-Thy 1.2 sera + C′ did not affect the generation of immunological memories nor the magnitude of the proliferative response of spleen cells to nonspecific T-cell mitogens in vitro, indicating that the cells responsible for such functions were host derived. Finally, the antibody-forming capacity of spleen cells derived from SRBC-primed ATxXB mice to the test antigen in vitro was completely abrogated by exposure to 450 R, whereas the helper function of the same cell suspension remained unaffected even after exposure to 1000 R. Implication of these findings on the nature of T cells resident in spleens of ATxXB mice was discussed.     

Analyses of acute graft-versus-host-like reaction in [MRL/lpr----MRL/+] chimeric mice using MRL/lpr-Thy-1. 1 congenic mice.

When MRL/Mp(-)+/+(MRL/+) mice are lethally irradiated and then reconstituted with MRL/Mp-lpr/lpr (MRL/lpr) bone marrow and/or spleen cells, these MRL/+ mice develop "lpr-GVHD" which is similar to acute graft-versus-host disease (GVHD). Using a Thy-1 congenic strain of MRL/lpr mice (MRL/lpr-Thy-1.1), we analyzed T cell subpopulations in the thymus and spleen of MRL/+ mice suffering from lpr-GVHD. lpr-GVHD was induced in MRL/+ mice by transplantation of bone marrow cells (BMC) from MRL/lpr-Thy-1.1 mice; severe lymphocyte depletion associated with fibrosis was observed in the spleens after 7 weeks of bone marrow transplantation (BMT). Thymocytes of the host MRL/+ thymus were replaced with donor-derived cells from the early stage of lpr-GVHD, whereas in the spleen, a small number of host T cells (Thy-1.2+) (4-5%) were retained until the late stage of lpr-GVHD. Donor-type (Thy-1.1+) T cell subsets were not different from those of nontreated MRL/+ mice in the thymus, whereas in the spleen. CD8+ T cells (Thy-1.1+) reached a peak at 5 weeks after BMT, and CD4+ T cells (Thy-1.1+), a peak at 6 weeks. The elimination of T cells from MRL/lpr BMC had no evident effect on the prevention of lpr-GVHD. T cell subpopulations showed a similar pattern to GVHD elicited by MHC differences. Analyses of autoreactive T cells expressing V beta 5 or V beta 11 revealed that autoreactive T cells were deleted from the peripheral lymph nodes. Interestingly, the levels of IgG anti-ssDNA antibodies markedly increased, and both IgM and IgG rheumatoid factors slightly increased 5 to 7 weeks after BMT. These findings are discussed in relation to not only GVHD elicited by MHC differences but also autoimmune diseases.     

Cells involved in cell-mediated and transplantation immunity in the rabbit. IV. The organ localization of the cells capable of migrating in vitro. Inhibition of migration by immunizing antigen

Rabbits were immunized with ovalbumin emulsified in complete Freund's adjuvant subcutaneously or with ovalbumin (OA) in saline intravenously. They were skin tested at intervals of time in order to determine the optimal sensitization time for the induction of the delayed skin reaction. The rabbits were also sacrificed and cell suspensions were prepared from the following organs: spleen, thymus, bone marrow, lymph nodes (popliteal), appendix, sacculus rotundus, and Peyer's patches. Peritoneal exudate cells were also obtained. These cell suspensions were tested for their ability to be inhibited in their migration in vitro by the specific sensitizing antigen. It was observed that the migration of all of the cell suspensions except for the bone marrow and peritoneal exudate cells could be inhibited by OA, but not by BGG, a non-cross-reacting antigen. Inhibition of migration was most marked at 3–4 weeks postsensitization and was negligible by 8–12 weeks, at a time when the delayed skin reaction was as extensive as in the early postsensitization period. Furthermore, the migration of cells of rabbits immunized with OA in saline intravenously was also markedly inhibited. It is concluded that, in the rabbit, different cell pathways are operative in the induction of the delayed skin reaction, on the one hand, and the facilitation of migration inhibition, on the other.     

Studies on the maturation of immune responsiveness in the mouse. II. Role of the spleen.

Experiments were designed to investigate the role of the spleen in the development of the murine immune system. By using mice splenectomized within 24 hr of birth, as well as mice with a hereditary, congenital absence of the spleen, the primary immune response to sheep erythrocytes was examined. The immunocompetence of lymph node cells from spleenless or control mice was assessed in vitro, in organ and in cell suspension cultures, and in vivo, by transfer into lethally irradiated syngeneic recipients followed by antigenic stimulation. The immunologic capacities of thymus and bone marrow cells were similarly tested by injection separately or in combination into irradiated syngeneic mice. Lymph node cells from spleenless animals appeared fully competent both in vitro and in transfer experiments. Neither neonatal splenectomy nor congenital absence of the spleen significantly reduced the capacity of bone marrow or thymus cells to participate in the immune response to sheep erythrocytes.     

CFU-S and haematopoietic microenvironment in mice after fractionated irradiation. A study on spleen colonies.

The paper is aimed at evaluating the quantity and quality of the haematopoietic stem cells, CFU-S, in the bone marrow and the functional effectiveness of the haematopoietic microenvironment of the spleen in two time intervals after repeated exposure of mice to doses of 0.5 Gy gamma-rays once a week (total doses of 12 and 24 Gy). After irradiation, bone marrow was cross-transplanted between fractionatedly irradiated and control mice. The parameter evaluated were numbers of spleen colonies classified into size categories. The data obtained provide evidence for a significant damage to the CFU-S, concerning both their number and proliferation ability, after both total doses used. The functional effectiveness of the haematopoietic microenvironment of the spleen was impaired only in bone marrow recipients receiving a transplant after having been exposed to a total dose of 24 Gy; this dose combined with subsequent pre-transplantation irradiation resulted in a marked suppression of cell production within the spleen colonies formed from a normal bone marrow on the spleens of fractionatedly irradiated mice.     

Studies on the resistance to tolerance induction against human IgG in DDD mice. III. Development of the resistance with age and cellular events.

Three-week-old DDD mice were easily rendered tolerant to human IgG while 12-week-old mice were tolerized only partially. Mechanisms of the development of the resistance with age were investigated. It was shown by the cell transfer experiments that spleen T cells, purified on a Tetron wool column, from older mice were responsible for the resistance, which was not associated with the loss of suppressor cells with age. To elucidate the possibility of whether tolerogen-sensitive spleen T cells differentiate into resistant ones, cell transfer experiments were carried out in which thymectomized, lethally irradiated mice were reconstituted with spleen cells from 3-week-old mice and then treated with the tolerogen on various days afterward. The results indicated that tolerance was inducible in these hosts to the same degree, irrespective of the timing of the tolerogen injection, while age-matched intact mice gradually acquired the resistance. Then the possibility of whether age of thymus affected tolerance inducibility of the hosts or not was examined. The tolerogen was injected into irradiated, bone-marrow-reconstituted mice which bore either 4- or 7-week-old thymus. It was shown that helper T cells newly generated under younger thymus acquired higher susceptibility to the tolerogen. There was no difference in tolerance inducibility irrespective as to whether bone marrow cells were prepared from younger or older mice. From these observations it was suggested that the resistance to tolerance induction in DDD mice is acquired through the appearance of resistant T cells which are generated from T-cell precursors in bone marrow under the influence of a radioresistant thymic constitution and predominantly located in the spleen.     

In vitro immune response to the 2,4,6-trinitrophenyl determinant in aged C57BL/6J mice:changes in the humoral immune response to, avidity for the TNP determinant and responsiveness to LPS effect with aging.

An in vitro anti-TNP response of the spleen cells from aged C57BL/6J mice showed approximately 4-fold less PFC than did that from young adult mice. Anti-theta serum-treated young spleen cells gave an anti-TNP response that was definitely greater than the response of the anti-theta serum-treated aged spleen cells in the presence of the exogenous activated thymus cells as helper cells. These results suggest that the deficits in B cells may be partly responsible for the imparied anti-TNP response of the aged spleen cells. To examine further the capacity of stem cells in the bone marrow to generate B cells responsible for anti-TNP response in the spleen, we injected i.v. 1.5 to 2.0 times 10(7) bone marrow cells from young or aged mice into lethally irradiated syngeneic recipients that had previously been thymectomized. Four to 6 weeks later, 10(7) spleen cells from the two groups of these recipient mice were immunized with TNP-SRBC in the presence of the exogenous activated thymus cells and assayed for anti-TNP PFC. The response of the aged marrow-derived B cells was approximately one-half of that of the young marrow-derived B cells.The avidity for TNP determinant of the antibodies produced by the PFC was determined by the plaque-inhibition technique. The avidity of the antibodies produced by the aged mice was approximately 33 times lower than that by the young mice. Anti-TNP response of the young spleen cells were markedly enhanced by the addition of LPS to the cultures, whereas no or little enhancement of the response was induced in the aged spleen cells even in the presence of high concentration of LPS. In contrast, DNA synthesis of both the young and aged spleen cells was comparably stimulated by 1 mug/ml and 10 mug/ml of LPS, however, it was rather less in the aged spleen cells at a concentration of 100 mug/ml. Mechanisms responsible for the changes in avidity and responsiveness to LPS with aging are discussed.     

Cellular aspects of tolerance. I. Parameters of tolerance induction in T cells of spleen and thymus

Unresponsiveness of T cells in thymus and spleen of tolerant animals was determined by reconstitution of lethally irradiated recipients. The degree of responsiveness of these animals was assessed by antigen elimination and two types of plaque assays (liquid and agar) with different sensitivity. Unresponsiveness occurred more rapidly in T spleen cells than in thymus cells. Unresponsiveness of T cells could be induced in the spleens of thymectomized animals and in T cell repopulated thymectomized lethally irradiated recipients. Induction of unresponsiveness did not depend on proliferating bone marrow cells or on accessory cells.     

Regulation of the in vitro anamnestic antibody response by cyclic AMP. II. Antigen-dependent enhancement by exogenous prostaglandins of the E series.

The spleen cells from CFW/D mice injected with dimethylbenzanthracene-induced leukemia virus exhibited a progressive decline in the in vitro response to heterologous erythrocyte antigens in parallel with tumor growth. Cell transfer experiments revealed that this immunodepressed state may involve a B-cell defect rather than extrinsic factors in the cellular environment since: (i) nonresponsiveness could be transferred to irradiated non-tumor-bearing mice with spleen cells, and (ii) T cells from tumorbearing mice cooperated with normal bone marrow cells, but bone marrow from tumorbearing mice did not cooperate with normal T cells. In addition, T cells from the thymic tumor could cooperate with normal bone marrow cells upon transfer to irradiated recipients. TL 485-2 cells, a T-cell line derived from the tumor, could be specifically activated with SRBC thereby indicating that the virus transformed T cells were immunocompetent. Suppressor cells, which appeared in the spleen concomitant with immunodepression and tumor development, may directly raise B-cell thresholds for T-dependent triggering signals since the antibody response of spleen cells from tumor-bearing mice could be restored by adding agents such as LPS, 2 mercaptoethanol, or T cells exogenously preactivated in normal animals. The suppressor cell could be enriched by adherence to plastic and was removed by treatment with carbonyl iron. In addition, it was unlikely that the suppressor cell was a virus-infected cell since transformed, virus-infected cells from the tumor or TL 485-2 cells were not suppressive when added to spleen cells in vitro but rather resulted in a marked, polyclonal enhancement of the PFC response. The interaction of TL 485-2 cells and normal spleen cells resulted in the release of a stimulatory factor which increased DNA synthesis in resting cells as well as increasing PFC. The role of these enhancing factors and suppressor cells in controlling tumor growth remains to be elucidated.     

Further studies on Th-B, a cell surface antigenic determinant present on mouse B cells, plasma cells and immature thymocytes.

A goat antiserum (Goat anti-M104E) has been produced which contains antibodies selectively cytotoxic for mouse B cells and a subpopulation of thymus cells. It reacts with the Th-B antigenic determinant which has been shown by us (1–3) to be present on B cells and on plasma cells and on some cells in the thymus. It also is very cytotoxic for mouse B cells while a previously developed rabbit antiserum was not. The antiserum was obtained by immunization with cells of the BALB/c mouse myeloma MOPC-104E. When the antiserum was purified by in vivo absorption in mice, antibodies remained which were cytotoxic for cells of all of several myelomas at a titer between 1:128 and 1:1024 as determined by an in vitro complement dependent cytotoxicity test. The in vivo purified antibodies were also cytotoxic for about 70% of thymus cells, for about 70% of spleen cells, for about 50% of lymph node cells and for about 20% of bone marrow cells. They were very cytotoxic for splenic or lymph node B cells separated from T cells by a nylon wool column and only slightly cytotoxic for splenic or lymph node T cells. The antibodies were only weakly cytotoxic for one out of five T cell tumors tested and not cytotoxic for the remaining four. Irrespective of target cells used, the cytotoxicity of purified Goat anti-M104E was easily removed by absorption with cell suspensions from tissues which contain B cells, plasma cells or thymus cells. In order to confirm that the same anti-Th-B antibodies recognize the determinant present on spleen cells and on some thymocytes, the purified Goat anti-M104E serum was absorbed with either spleen cells or thymus cells. The absorbed sera were tested for ability to label thymocytes or spleen cells using the fluorescence activated cell sorter (FACS). Either absorption removed essentially all the antibody capable of binding to either cell population. In addition it was shown, using the FACS, that only B cells and not T cells of the spleen contain the Th-B determinant. The anti-Th-B antibodies have now been used for the rapid elimination of B cells from a mixed population of lymphocytes without affecting the function of mature T cells. Thus in vitro treatment of spleen cells from SRBC-immunized donors with purified Goat anti-M104E plus complement results in the killing of a high proportion of the B memory cells as shown by the reduction of PFC produced when the treated cells are transferred to irradiated recipients. The T cell helper function of the transferred cells is not affected by Goat anti-M104E treatment as shown by appropriate cell transfer experiments in which effective B cells are provided by an AKR anti-Thy-1.2-treated spleen cell population and effective T cells are provided by the Goat anti-M104E-treated spleen cell population. Antibodies detecting Th-B may serve as an approach to understanding the ontogeny of lymphocytes. Our results suggest that Th-B is a cell surface marker appearing early in the development of lymphoid cells, on the common precursor of B and T cells and that it is lost from T cells as they mature in the thymus.     

Suppression of antibody responses in allogeneic mice by products of lymphoid tissue. I. Allogeneic suppressive factor (ASF) from spleens repopulated with thymus cells.

A cellfree extract prepared from the spleen cells of C3H mice is capable of suppressing antibody responses to SRBC when extract material is exposed to alloantigens. The observed immunosuppression was attributed to a soluble factor in the extract. This allogeneic suppressive factor (ASF) was detected in extracts prepared from the spleen cells of unirradiated mice as well as those of irradiated mice repopulated with thymocytes, provided that mice were previously immunized with SRBC. Donors of actively suppressive ASF preparations did not need to be previously exposed to alloantigens. Extracts from thymus and marrow cells of unirradiated mice and the spleen cells of irradiated mice repopulated with marrow cells (or no cells) did not contain ASF. C3H thymocytes stimulated with SRBC generated more ASF activity in spleens of C3BF1 hosts than in those of C3H hosts, indicating that alloantigenic stimulation enhances the production or activity of ASF. Once produced, C3H ASF was able to suppress antibody responses in cell transfer experiments only if exposed to C3BF alloantigens of either donor lymphoid cells or irradiated hosts. Once exposed to alloantigens, ASF appears to be capable of suppressing antibody responses of syngeneic C3H or semi-allogeneic C3BF cells. When both donor lymphoid cells and hosts were syngeneic with the donor of the ASF, there was enhancement of antibody formation in cell transfer experiments. C3H ASF did not interfere with education of C3BF thymocytes to SRBC or with the generation of precursors of anti-SRBC antibody-forming cells by C3BF1 marrow cells. ASF may interfere with cellular cooperative events necessary for humoral immune responses or with terminal differentiation of B cells. Production of ASF could partially account for the suppression of antibody responses observed during graft-vs-host reactions.     

Cell transfer studies in cyclophosphamide-induced tolerance

Thymectomized, irradiated adult CBA mice were restored with various combinations of bone marrow and thymus cells from nontolerant animals and from animals made tolerant to sheep erythrocytes or to hemocyanin with the drug cyclophosphamide. Mice reconstituted with tolerant marrow and thymus responded as well as those that received nontolerant cells. Thus it is concluded that the tolerant state of the transferred marrow and thymus cells is not a significant factor in the tolerant state of the recipient, and that antigenic diversity is restored in the interaction and proliferation of bone marrow and thymus cells that follow transfer.Thymectomized irradiated mice restored with thymocytes, in contrast to unoperated animals, require multiple antigen injections to demonstrate comparable immune response, but develop tolerance normally when treated with cyclophosphamide and antigen. Reconstitution with tolerant marrow and thymus cells resembles the recovery of immune responsiveness seen after lethal irradiation of tolerant mice; in both instances a complete breakdown of immunological tolerance is observed.     

Antigenic markers on mouse lymphoid cells: origin of cells mediating immunologic memory

Specific antisera were used for the purification of thymus dependent and thymus independent or bursa equivalent lymphoid cells in the mouse. Spleen cells from mice immune to sheep erythrocytes, a thymus dependent antigen, or to E. coli 055:B5 lipopolysaccharide, a thymus independent antigen, were treated with anti-θ (C3H) serum or anti-MBLA serum and complement prior to their adoptive transfer into lethally irradiated syngeneic recipients. Syngeneic thymocytes, bone marrow cells, or spleen cells from nonimmune donors were appropriately added to antiserum treated cells prior to transfer. The secondary response to these antigens was assayed in recipient spleens six days after cell transfer. The kinetics of the primary response to SRBC was investigated as to its effect on origin of specific hyper-reactive T or B lymphoid cells.The adoptive response to CPS originated in the B lymphoid cell population. Immunologic memory to CPS was demonstrated in recipients of immune cells, compared to recipients of normal cells, by a five fold increase in antibody forming cells.The IgM and IgG adoptive immune response to high doses of SRBC depended upon an increased number of specifically hyper-reactive T-lymphoid cells to facilitate cooperation between T and B lymphocytes. High doses of SRBC initially stimulated T cell memory but at 42 days after priming an increased number of specifically hyper-reactive B lymphoid cells were present.     

Radioprotection by whole body hyperthermia: possible mechanism(s)

Studies were carried out to gain an insight into the mechanisms underlying WBH induced radioprotection. The plasma levels of IL-1α, IL-6, TNF-α and GM-CSF, were elevated in WBH treated mice between 2 and 6 h after treatment. The total nucleated cell count of hemopoietic tissues such as spleen, thymus, bone marrow and peripheral blood showed drastic reduction without recovery until death in mice treated with TBI. However, the nucleated cell count in the above tissues showed significant recovery after initial drop in WBH and WBH+TBI treated groups and reached to a normal level by day 7 and day 28, respectively. The total WBC and RBC count in peripheral blood recovered to a control level by day 28 after treatment. Significant number of endogenous spleen colonies were detected, 14 days after TBI in WBH pre-treated mice whereas no such spleen colonies could be detected in TBI treated group. The transplantation of bone marrow derived from control, WBH, TBI and WBH+TBI treated groups of mice to lethally irradiated mice (8 Gy) showed formation of spleen colonies only in mice which received bone marrow from control, WBH and WBH+TBI treated groups. Transplantation of the bone marrow from these groups of mice resulted in prolonged survival of lethally irradiated mice as compared to mice receiving bone marrow from TBI treated mice. These results seem to suggest that WBH induced radioprotection of mice could be due to immunomodulation manifested through induction of cytokines responsible for protection and proliferative response, leading to accelerated recovery from hemopoietic damage-a major cause of radiation induced death.     

Radiation-induced alterations in murine lymphocyte homing patterns: I. Radiolabeling studies

In vitro X-irradiation of ⁵¹Cr-labeled spleen, lymph node, bone marrow, or thymus cells was found to alter their subsequent in vivo distribution significantly in syngeneic BDF₁ mice. Irradiated cells demonstrated an increased distribution to the liver and a significantly lower retention in the lungs. Cells going to the lymph nodes or Peyer's patches showed a significant exposure-dependent decrease in homing following irradiation. Irradiated lymph node cells homed in greater numbers to the spleen and bone marrow, while irradiated cells from other sources showed no preferential distribution to the same tissues. Sampling host tissues at various times after irradiation and injection did not demonstrate any return to normal patterns of distribution. The alterations in lymphocyte homing observed after in vitro irradiation appear to be due to the elimination of a selective population of lymphocytes or membrane alterations of viable cells, and the detection of these homing changes is in turn dependent upon the relative numbers of various lymphoid subpopulations which are obtained from different cell sources. Radiation-induced alterations in the normal homing patterns of lymphoid cells may thus be of considerable importance in the evaluation of subsequent functional assays in recipient animals.