Defect in negative selection in lpr donor-derived T cells differentiating in non-lpr host thymus.

Transplantation of bone marrow cells of lpr/lpr mice into irradiated normal mice fails to develop massive lymphadenopathy or autoimmunity but causes severe graft-vs.-host-like syndrome. To elucidate an abnormality of lpr/lpr bone marrow-derived T cells, we transplanted bone marrow cells of Mlsb lpr/lpr mice into H-2-compatible Mlsa non-lpr mice. Although lpr/lpr T cell precursors repopulated the host thymus as well as +/+ cells, a proportion of CD4+CD8+ cells decreased, and that of both CD4- and CD8- single-positive cells increased compared with those of +/+ recipients. Notably, in MRL/lpr----AKR and C3H/lpr----AKR chimeras, CD4 single-positive thymocytes contained an increased number of V beta 6+ cells in spite of potentially deleting alleles of Mlsa, whereas V beta 6+ mature T cells were deleted in the MRL/+ ----AKR and C3H/+ ----AKR chimeras. There was no difference between MRL/+ ----AKR and MRL/lpr----AKR chimeras in their proportion of V beta 3+ cells because both host and donor strain lack the deleting alleles. Interleukin 2 receptor expression of mature T cells, in the thymus and lymph node, was obviously higher in the MRL/lpr----AKR chimeras, in particular in the "forbidden" V beta 6+ subset. Moreover, lpr donor-derived peripheral T cells showed vigorous anti-CD3 response. These results indicate that lpr-derived T cells escape not only tolerance-related clonal deletion but also some induction of unresponsiveness in the non-lpr thymus.

Maturational arrest from CD4+8+ to CD4+8- thymocytes in a mutant strain (LEC) of rat.

A mutant strain (LEC) of rats was found to have a novel defect in T cell maturation, that is, arrest of differentiation from CD4+8+ to CD4+8- but not to CD4-8+ thymocytes. FACS analyses demonstrated a deficiency in the CD4+8- T cell subset in the thymus and a marked decrease in CD4+ T cells in peripheral lymphoid organs. Expression of the T cell receptor (TCR)/CD3 complex in CD4+8+ and CD4-8+ thymocytes of LEC rats was normal. Expression of class II major histocompatibility complex (MHC) in the thymus of LEC rats was also the same as that of normal rats. These results indicate that maturational arrest occurs only in the transition pathway from CD4+8+ to CD4+8- thymocytes, and that this mutation can not be attributed to the default of expression of either TCR/CD3, CD4, or class II MHC antigen. Consequently, dysfunction of helper T cells was observed in LEC rats, while killer T cells and B cells functioned normally. Although the complete identification of the origin of this mutation requires further studies, it is hoped that such investigations will throw light on the mechanism of positive selection.

Identification and characterization of novel multiple bacteriocins produced by Leuconostoc pseudomesenteroides QU 15.

AIM: To characterize novel multiple bacteriocins produced by Leuconostoc pseudomesenteroides QU 15. METHODS AND RESULTS: Leuconostoc pseudomesenteroides QU 15 isolated from Nukadoko (rice bran bed) produced novel bacteriocins. By using three purification steps, four antimicrobial peptides termed leucocin A (ΔC7), leucocin A-QU 15, leucocin Q and leucocin N were purified from the culture supernatant. The amino acid sequences of leucocin A (ΔC7) and leucocin A-QU 15 were identical to that of leucocin A-UAL 187 belonging to class IIa bacteriocins, but leucocin A (ΔC7) was deficient in seven C-terminal residues. Leucocin Q and leucocin N are novel class IId bacteriocins. Moreover, the DNA sequences encoding three bacteriocins, leucocin A-QU 15, leucocin Q and leucocin N were obtained. CONCLUSIONS: These bacteriocins including two novel bacteriocins were identified from Leuc. pseudomesenteroides QU 15. They showed similar antimicrobial spectra, but their intensities differed. The C-terminal region of leucocin A-QU 15 was important for its antimicrobial activity. Leucocins Q and N were encoded by adjacent open reading frames (ORFs) in the same operon, but leucocin A-QU 15 was not. SIGNIFICANCE AND IMPACT OF STUDY: These leucocins were produced concomitantly by the same strain. Although the two novel bacteriocins were encoded by adjacent ORFs, a characteristic of class IIb bacteriocins, they did not show synergistic activity.

Augmentation of tumor immunity against syngeneic tumors in mice by beta-carotene.

The effect of beta-carotene on tumor immunity was examined with the use of a syngeneic murine tumor system. Oral administration of beta-carotene (120 micrograms/mouse/day) for 9 days from day 1 to the BALB/c mice inoculated sc with 10(7) syngeneic BALB/c Meth A fibrosarcoma cells (Meth A) led to a remarkable rejection against rechallenged Meth A implanted sc on day 10. The growth of Meth 1 fibrosarcoma (Meth 1), another syngeneic tumor of BALB/c origin, as a rechallenge tumor was unaffected by treatment with beta-carotene, thereby suggesting that beta-carotene may augment tumor rejection specific to tumor-specific antigens. Winn assay revealed that the suppressive effect on tumor growth of immune lymph node cells obtained from Meth A-inoculated beta-carotene-treated mice on day 12 was enhanced dose dependently. Primary effector cells responsible for the augmented rejection are Thy-1-positive, Lyt-1-negative, and Lyt-2-positive lymphocytes, presumably cytotoxic T-lymphocytes.

Combined treatments with vitamin A and 5-fluorouracil and the growth of allotransplantable and syngeneic tumors in mice.

The combined effect of retinol palmitate (RP) and 5-fluorouracil (FUra) was examined with the use of allotransplantable and syngeneic murine tumor systems. The ip combined administration of RP (5,000 IU/kg/day) and FUra (5 mg/kg/day, 20 mg/kg/day, or 20 mg/kg/every 3d day) suppressed the tumor growth in ICR/JCL mice given sc inoculations of 5 X 10(6) allotransplantable sarcoma 180 cells and prolonged the survival time of mice inoculated ip with 10(7) tumor cells, as compared with the survival time of mice given the single administration of either RP or FUra. Similar results were obtained when BALB/c mice were inoculated sc with a syngeneic BALB/c Meth A fibrosarcoma and treated with RP (5,000 IU/kg/day) and FUra (20 mg/kg/every 3d day). The growth of Meth A implanted on day 10, as a rechallenge, was significantly suppressed in the group pretreated with RP alone or both RP and FUra for 9 days from day 1. The growth of Meth 1, another syngeneic tumor of BALB/c origin, inoculated on day 10 as a rechallenge tumor was unaffected by the treatment with RP and/or FUra. An immune response to tumor-specific antigens seemed to be involved in the combined effects of these two drugs.

Mechanisms of the potentiation of specific antitumor immunity by intratumor injection of Corynebacterium parvum.

Meth A fibrosarcoma-bearing BALB/c mice given intratumoral injections of 0.5 mg of Corynebacterium parvum showed a highly and tumor-specific transplantation antigen specifically potentiated concomitant immunity to a subsequent tumor challenge. This potentiated antitumor immunity could be locally transferred in the Winn assay to normal recipients with whole draining lymph node cells from the tumor-bearing mice, but the potentiated effect disappeared when adherent cells were removed from these cells. Moreover, the potentiated cytostatic effect on tumor cells was detected in the peritoneal macrophages but not in the nonadherent draining lymph node cells in in vitro tests. On the other hand, nonadherent draining lymph node cells from the tumor-bearing mice, when mixed with C. parvum-induced macrophages, exhibited a specifically potentiated antitumor effect. In addition, this effect was completely abolished by treatment of the draining lymph node cells with anti-Thy-1 and complement. Thus, the potentiated antitumor effect following intratumor injection of C. parvum may be ascribed to the collaboration of specifically sensitized T-lymphocytes with C. parvum-activated macrophages.

Hypothalamic neuronal histamine as a target of leptin in feeding behavior.

Leptin, an ob gene product, has been shown to suppress food intake by regulating hypothalamic neuromodulators. The present study was designed to examine the involvement of brain histamine in leptin-induced feeding suppression. A bolus infusion of 1.0 microg leptin into the rat third cerebroventricle (i3vt) elevated the turnover rate of hypothalamic neuronal histamine (P < 0.05) as assessed by pargyline-induced accumulation of tele-methylhistamine (t-MH), a major metabolite of histamine. No remarkable change in the mRNA expression of histidine decarboxylase (HDC), a histamine-synthesizing enzyme, was observed in the hypothalamus after i3vt infusion of leptin. These results indicate that leptin increases histamine turnover by affecting the posttranscriptional process of HDC formation or histamine release per se. As expected, concomitant suppression in 24-h cumulative food intake was also observed after infusion of leptin. Systemic depletion of brain histamine levels by pretreatment with an intraperitoneal injection of 224 micromol/kg alpha-fluoromethylhistidine (FMH), a suicide inhibitor of HDC, attenuated the leptin-induced feeding suppression by 50.7% (P < 0.05). This attenuation of feeding suppression was mimicked by the i3vt infusion of 2.24 micromol/kg FMH before leptin treatment (P < 0.05). In addition, concentrations of hypothalamic histamine and t-MH were lowered in diabetic (db/db) mice, which are known to be deficient in leptin receptors (P < 0.05 vs. lean littermates for each amine), although the amine levels were higher in diet-induced obese rats (P < 0.05 for each amine). Leptin-deficient obese mice (ob/ob) showed lower histamine turnover (P < 0.05 vs. lean littermates), which recovered after leptin infusion. Thus, a growing body of results points to an important role for the hypothalamic histamine neurons in the central regulation of feeding behavior controlled by leptin.

Different cytokines are required for induction and maintenance of the Th2 type response in DBA/2 mice resistant to infection with Leishmania major.

Experimental cutaneous leishmaniasis is a useful model in studying the mechanism regulating immune responses between T helper type 1 (Th1) and Th2. Mice susceptible to Leishmania major infection such as BALB/c (H-2(d)) are associated with the induction of the disease-promoting Th2 response, while the resistant mice such as DBA/2 (H-2(d)) develop the protective Th1 response. To understand the induction mechanism of Th1 and Th2 responses, it is necessary to establish an immunization scheme by which the induction of each Th response can be easily and experimentally controlled. Adjuvants are known to enhance the immune responses through the combined effect of several factors: prolonged release of antigen, migration of cells, mitogenic effect and so forth. When the genetically resistant DBA/2 mice were immunized twice with soluble leishmanial antigen (SLA), emulsified in incomplete Freund's adjuvant (IFA) before L. major inoculation, these mice mounted a Th2 cell response and suffered from progressive infection. While IL-4 and IL-13 were upregulated early after the infection in both healer and non-healer groups of mice, IL-5 and IL-10 were upregulated only in non-healer mice. From these results, IL-5 and IL-10 appear to have an important role, at least in the early phases of the infection, rather than IL-4 and IL-13 in establishing the disease-promoting Th2 response in leishmaniasis. Further, IL-9 was found to be expressed in both BALB/c and DBA/2 mice immunized with IFA/SLA. This cytokine may support the establishment of a Th2 response in these mice. Therefore it is suggested that Th2 cytokines play different roles between priming and maintaining the Th2 immune response after the infection.

Antibodies specific for heat shock proteins in human and murine malaria.

Heat shock proteins (HSPs) are immunodominant antigens recognized by the host immune system in various infectious diseases. We analyzed HSP-specific antibodies, including immunoglobulin G (IgG), IgM and IgA, in sera from malaria patients in Thailand by using an enzyme-linked immunosorbent assay. All of the antibodies to HSP90 were remarkably increased in the patients compared with those in controls, while only IgM to HSP70 or IgA to HSP65 was significantly elevated. Further experiments showed that anti-HSP IgG was significantly increased in C57BL/6 mice infected with a non-lethal strain of Plasmodium yoelii, with anti-HSP90 IgG being the most elevated. These results suggest that the antigenic potential of HSP90 is higher than those of HSP70 and HSP65 in malaria infection.

Expression and role of heat-shock protein 65 (HSP65) in macrophages during Trypanosoma cruzi infection: involvement of HSP65 in prevention of apoptosis of macrophages.

The 65-kDa heat-shock protein (HSP65) is thought to play a role in host defense against infections with various microbial pathogens and in autoimmune inflammatory disorders. We investigated the biological function and expression mechanism of HSP65 in macrophages of mice infected with Trypanosoma cruzi. BALB/c mice, which are susceptible to T. cruzi, showed high levels of parasitemia, and 80% of these mice died within 42 days after the infection, whereas resistant C57BL/6 or DBA/2 mice showed low levels of transient parasitemia and all survived. HSP65 expression was correlated with resistance to T. cruzi infection; HSP65 was more strongly expressed in macrophages of resistant C57BL/6 and DBA/2 mice than in macrophages of susceptible BALB/c mice. Immunodeficient BALB/c-nu/nu (nude) and C.B-17 scid/scid (SCID) mice were shown to be highly susceptible to this infection, and they did not express detectable levels of HSP65, suggesting that T cells play essential roles in the expression of HSP65 as well as in protective immunity against the infection. CD4(+) T cells, but not CD8(+) T cells or gammadelta T cells, were the cell population responsible for the induction of HSP65 expression in macrophages. Furthermore, depletion of asialo GM-1(+) NK cells made resistant C57BL/6 mice more susceptible to the infection, and HSP65 expression in their macrophages was abolished. Semiquantitative reverse transcription PCR analyses showed that both interferon gamma (IFN-gamma) and tumor necrosis factor alpha (TNF-alpha) mRNA levels in CD4(+) T cells became low when resistant C57BL/6 mice were depleted of NK cells, suggesting that NK cells contribute to functional differentiation of CD4(+) T cells and thereby affect the induction of HSP65 expression. To determine the function of HSP65, macrophages were treated in vitro with antisense oligonucleotide for HSP65 prior to inducing HSP65 with IFN-gamma plus TNF-alpha or T. cruzi infection. This treatment did not affect the production of nitric oxide following activation, but the treated macrophages became susceptible to apoptosis. These results indicate that HSP65 plays a role in preventing the apoptosis of macrophages and thereby contributes to host resistance against T. cruzi infection.

Contribution of 65-kDa heat shock protein induced by gamma and delta T cells to protection against Toxoplasma gondii infection.

Heat shock proteins (HSPs) are evolutionarily highly conserved polypeptides synthesized by many cells to preserve cellular functions under a variety of stressful conditions including infections. We have investigated the involvement of 65-kDa HSP (HSP65) in host protection against an intracellular protozoan parasite, Toxoplasma gondii, in mice. Experiments using low and highly virulent strains of Tox. gondii revealed that induction of murine HSP65 on macrophages closely correlates with protection against infection with this protozoan. Furthermore, we clarified that T cells, especially gamma delta T cells, are indispensable for HSP65 expression. A similar relationship between the expression of HSP65 on host macrophages and protective immunity was observed in mice infected with Leishmania major and Trypanosoma cruzi, both of which are obligate intracellular protozoa as is Tox. gondii.

Molecular characterization of a 2-Cys peroxiredoxin from the human malaria parasite Plasmodium falciparum.

We have identified the 2-Cys peroxiredoxin (PfPrx-1) from the human malaria parasite Plasmodium falciparum. The PfPrx-1 showed the highest identity at amino acid level to the type II Prx among the currently known six subfamilies of mammalian Prx. The sequence identity between the PfPrx-1 and the previously reported 1-Cys Prx of P. falciparum (PfPrx-2), which corresponded to mammalian type VI Prx, was 25%. This suggests that the parasite possesses two Prx subfamilies. The PfPrx-1 showed significant sequence similarities with those of 2-Cys peroxiredoxins of plants in the BLASTX search. This may reflect the consequences of a genetic transfer from an algal endosymbiont to the parasite nucleus during evolution. The recombinant PfPrx-1 protein (rPfPrx-1) was expressed as a histidine fusion protein in Escherichia coli and purified with Ni chromatography. The rPfPrx-1 existed as dimers under non-reducing conditions and dissociated into monomers in the presence of dithiothreitol. The PfPrx-1 protein also exists as a dimer in the parasites themselves. The reduction of the oxidized enzyme by the donation of electrons from E. coli thioredoxin (Trx)/Trx reductase system was demonstrated in its reaction with H(2)O(2), using the rPfPrx-1 protein. These results suggested that the PfPrx-1 can act as a terminal peroxidase of the parasite Trx system. An elevated expression of the PfPrx-1 protein seen in the trophozoite, the stage with active metabolism, suggests an association of the parasite Trx system with its intracellular redox control.

Drug-induced tolerance to allografts in mice. IV. Mechanisms and kinetics of cyclophosphamide-induced tolerance.

Mechanisms and kinetics of tolerance in AKR mice induced using i.v. priming with viable C57BL/6 spleen cells and treatment with cyclophosphamide 2 days later were analyzed. In this tolerance induction system, some lymphocyte populations mediating delayed foot-pad reaction and cytotoxic activity were resistant to tolerance induction and remained in a sensitized state after cyclophosphamide treatment. These populations were considered to be qualitatively distinct from populations sensitive to cyclophosphamide, because delayed foot-pad reaction and cytotoxic lymphocyte activity were stronger in tolerant mice than in control mice in the early stages of tolerance induction, but were not augmented after immunization with C57BL/6 spleen cells, C57BL/6 skin grafts, or EL4 tumor grafts in the absence of suppressor T cells. One of the important differences in these two lymphocyte populations may be the capacity for clonal expansion.

Drug-induced tolerance to allografts in mice. VI. Tolerance induction in H-2-haplotype-identical strain combinations in mice.

When C3H/HeN (C3H) mice were primed with viable AKR/J (AKR) spleen cells and treated with cyclophosphamide (CP) two days later, a profound tolerance to AKR skin grafts was induced. This tolerance was induced also in other combinations disparate only at minor histocompatibility (H) antigens (AKR-C3H and BALB/c[BALB]-DBA/2[DBA]). In C3H mice made tolerant to AKR, delayed foot-pad reaction (DFR), cytotoxic lymphocytes (CTL), and cytotoxic antibodies (CTAb) against AKR spleen cells were abrogated completely. Tolerance to AKR mice was also observed in C3H mice primed with viable AKR and C57BL/6 (B6) spleen cells and treated with CP, but tolerance to B6 was not induced because a cell population responsible for DFR and CTL against B6 H-2 antigens remained after tolerance induction. These results suggest that there is a lymphocyte population responsible for DFR and CTL against antigens allogeneic at both major and minor H that is less proliferative than the population responsible for DFR and CTL against minor H antigens.

The nature of tolerance in adult recipient mice made tolerant of alloantigens with supralethal irradiation followed by syngeneic bone marrow cell transplantation plus injection of F1 spleen cells.

The length of time after syngeneic bone marrow reconstitution when tolerance to alloantigens can be induced in adult mice during T cell differentiation from bone marrow cells was studied by exposing those T cells to (recipient x donor)F1 spleen cells. Supralethally irradiated C3H/He Slc(C3H; H-2k) mice were reconstituted with 1 x 10(7) syngeneic T cell-depleted bone marrow cells and then injected intravenously with 5 x 10(7) (C3H x C57BL/6[B6])F1 (B6C3F1; H-2bxk) or (C3H x AKR/J[AKR])F1 (AKC3F1; H-2kxk) spleen cells at various intervals. In the fully allogeneic combination of B6C3F1----C3H, EL-4 tumor originating from B6 was accepted, and survival of grafted B6 skin was significantly prolonged in the tolerant C3H mice treated with irradiation on day -1 followed by injection of syngeneic bone marrow cells on day 0 plus B6C3F1 spleen cells on days 0, 5, or 10, in a tolerogen-specific manner. In the multiminor histocompatibility antigen-disparate combination of AKC3F1----C3H, AKR skin grafts were permanently accepted in the tolerant C3H mice treated with AKC3F1 spleen cells on days 0, 5, 10, or 15. Immunological parameters, including cytotoxic T lymphocyte activity and delayed foot-pad reaction (DFR), were almost completely suppressed in C3H mice made tolerant of B6 or AKR antigens. A chimeric assay using a direct immunofluorescence method revealed that the tolerant C3H mice given B6C3F1 spleen cells on day 0 were mixed-chimeric for at least 8 weeks after syngeneic bone marrow reconstitution, but not definitely chimeric thereafter. The C3H mice given AKC3F1 spleen cells on day 0 were chimeric even 43 weeks after syngeneic bone marrow reconstitution, but the C3H mice given AKC3F1 spleen cells on day 15 showed temporal chimerism that disappeared within 43 weeks. The untolerant mice were never detectably chimeric. These data suggest that the earlier the timing of the injection of F1 spleen cells after syngeneic bone marrow reconstitution was, the more profound tolerance was induced. Moreover, the stronger the antigenic disparity between donor and recipient, the earlier the injection of F1 spleen cells was required to induce tolerance.

Drug-induced tolerance to allografts in mice. I. Difference between tumor and skin grafts.

When AKR mice were primed with viable C57BL/6(B6) spleen cells and treated with cyclophosphamide 1-3 days later, a profound tolerance to B6 tumor allografts was induced. The tolerant state was maintained completely for as long as 8 weeks. Although tumor allografts grew progressively even when inoculated after complete rejection of skin grafts, B6 skin grafts were rejected by tolerant mice. In mice tolerant of B6 tumors, production of cytotoxic antibody and cytotoxic activity was reduced profoundly, but the delayed-type hypersensitivity level decreased only slightly. We therefore presume that the decrease in cytotoxic activity may allow progressive growth of tumor allografts, but the maintenance of delayed-type hypersensitivity or a low level of cytotoxicity, or both, precludes acceptance of skin allografts.

Drug-induced in vitro tolerance to allogeneic antigens. II. Further analysis of in vitro-tolerized spleen cells in a fully allogeneic murine combination.

C3H/HeSlc (C3H, H-2k) spleen cells were made tolerant in vitro to C57BL/6CrSlc (B6, H-2b) at the cell-mediated cytotoxicity (CMC) level by in vitro stimulation for 48 hr with mitomycin C (MMC)-treated B6 spleen cells, and treatment with 5 micrograms/ml of 5-fluorouracil for a further 9 hr. These cells were given intraperitoneally to neonate (C3HxB6) F1 mice to examine whether these tolerized spleen cells would cause lethal graft-versus-host disease (GVHD). Despite the lack of CMC, the tolerized C3H spleen cells caused lethal GVHD in most of the neonate F1 mice. Evaluating from various immune parameters, it was evident that T cell populations responsible for IL-2 production, cytostasis, and delayed footpad reaction (DFR) were retained intact after in vitro tolerance induction, probably because of their less-proliferative characteristics in response to fully allogeneic antigen stimulation, and were considered to be responsible for lethal GVHD. Contribution of natural killer (NK) cells to lethal GVHD was not ruled out.

Drug-induced in vitro tolerance to allogeneic antigens. I. Establishment of a tolerance induction system in a fully allogeneic murine combination.

C3H/HeSlc (H-2k) spleen cells were cultured with mitomycin C (MMC)-treated C57BL/6CrSlc (H-2b) spleen cells for 2 days and incubated with 5-fluorouracil (5-FU) for a further 9 hr. Thereafter, those C3H/He spleen cells were recultured with the same allogeneic cells for 5 days. Cell-mediated cytotoxicity (CMC) and mixed lymphocyte reaction (MLR) were profoundly suppressed, antigen-specifically, in such C3H/He spleen cells. In contrast, interleukin 2(IL-2) production was not impaired in the restimulating mixed lymphocyte culture (MLC) with C57BL/6. Moreover, an adequate amount of exogenous IL-2 added to the restimulating MLC did not lead to a restoration of the depressed CMC. Suppressor cell activity in the CMC assay was not detected in the C3H/He spleen cells exposed to such a tolerance induction. These results suggest that the unresponsiveness to alloantigens in CMC and MLR was induced through a clonal deletion mechanism, and there may exist a 5-FU-resistant--thus less-proliferative--cell population that can produce IL-2 even after the tolerance induction.

Allograft rejection and immune responses against allogeneic antigens in neonatally thymectomized mice.

Skin allograft survival and immune responses against allogeneic antigens homologous to skin grafts were observed in BALB/c Cr Slc (BALB) mice (H-2d) thymectomized at 1 day after birth and grafted with skin from major histocompatibility complex (MHC)-incompatible, fully allogeneic C3H/HeN (C3H) (H-2k) or MHC-compatible allogeneic DBA/2 Cr Slc (DBA) mice (H-2d), at 14 weeks of age. In neonatally thymectomized (NTx) BALB mice, survival of C3H skin grafts was not prolonged at all, but survival of DBA skin grafts was prolonged significantly, although the survival periods of DBA skin grafts were very different among individual recipients. In NTx recipients grafted with C3H skin, delayed foot-pad reaction (DFR) was not reduced, but cytotoxic lymphocyte (CTL) activity and cytotoxic antibody (CTAb) production were appreciably depressed. CTL and CTAb were reduced profoundly and consistently in all NTx mice grafted with DBA skin, while DFR was reduced to various degrees in each. The degrees of depression of DFR in these NTx mice correlated well with the prolongation of DBA skin survival, although the sample number was small. The rejection of skin allografts appears to be attributable largely to a T cell subset, the function of which can be expressed as DFR. Thymus dependency in the ontogenic development is low as compared with other T cell subsets.

Drug-induced tolerance to allografts in mice. IX. Establishment of complete chimerism by allogeneic spleen cell transplantation from donors made tolerant to H-2-identical recipients.

Graft-versus-host reaction (GVH) after allogeneic spleen cell transplantation was completely suppressed in an H-2-matched murine combination (AKR/J Sea [H-2k]----lethally irradiated C3H/He Slc [H-2k]) by pretreatment of the donors with recipient spleen cell antigen plus cyclophosphamide (CP). Irradiated recipients receiving cells became chimeric. In contrast to the H-2 matched combination, lethal GVH reaction could not be prevented in an H-2-mismatched fully allogeneic combination (C57BL/6 Cr Slc [H-2b]----lethally irradiated C3H/He Slc [H-2k]) by pretreatment of the donors. The results suggest that the effectors responsible for the GVH reaction were abrogated by pretreatment of the donors with allogeneic recipient spleen cells plus CP in the H-2-matched combination, but donor pretreatment failed to abrogate GVH reaction in the H-2-mismatched combination.