Ability of thymic lymphocytes to alter CFU kinetics in radiation chimeras.

It is known that the poor colony-forming ability of B6 bone marrow transplanted into B6D2F1 hybrids can be improved if B6 lymphocytes are given in addition. It was recently reported that the augmenting lymphocytes decrease the doubling time of differentiating hemopoietic cells. To determine whether thymus cells alter the self-renewal of CFUs in this parent leads to F1 combination, retransplantation and 3H-thymidine 'suicide' were employed as methods to determine the cell-division rate. We have observed that in the presence of thymocytes, parental bone marrow cells are seeded more efficiently in the spleen, and the lag phase of the CFUs growth curve is shortened. However, thymic lymphocytes do not increase the slope of the exponential growth phase of CFUs.     

Cellular basis of the immunohematologic defects observed in short-term semiallogeneic B6C3F1 -- C3H chimeras: evidence for host-versus-graft reaction initiated by radioresistant T cells

Lethally irradiated C3Hf mice reconstituted with a relatively low dose (2 × 10⁶) of B6C3F₁ bone marrow cells (B6C3F₁ → C3Hf chimeras) frequently manifest immunohematologic deficiencies during the first month following injection of bone marrow cells. They show slow recovery of antibody-forming potential to sheep red blood cells (SRBC) as compared to that observed in syngeneic (C3Hf → C3Hf or B6C3F₁ → B6C3F₁) chimeras. They also show a deficiency of B-cell activity as assessed by antibody response to SRBC following further reconstitution with B6C3F₁-derived thymus cells 1 week after injection of bone marrow cells. A significant fraction of B6C3F₁ → C3Hf chimeras was shown to manifest a sudden loss of cellularity of spleens during the second week following injection of bone marrow cells even though cellularity was restored to the normal level within 1 week. The splenic mononuclear cells recovered from such chimeras almost invariably showed strong cytotoxicity against target cells expressing donor-type specific H-2 antigens (H-2^b) when assessed by ⁵¹Cr-release assay in vitro. The effector cells responsible for the observed anti-donor specific cytotoxicity were shown to be residual host-derived T cells. These results indicate strongly that residual host T cells could develop anti-donor specific cytotoxicity even after exposure to a supralethal dose (1050 R) of radiation and that the immunohematologic disturbances observed in short-term F₁ to parent bone marrow chimeras (B6C3F₁ → C3Hf) were due to host-versus-graft reaction (HVGR) initiated by residual host T cells. The implication of these findings on the radiobiological nature of the residual T cells and the persistence of potentially anti-donor reactive T-cell clones in long-surviving allogeneic bone marrow chimeras was discussed.     

Post-Irradiation Thymocyte Regeneration After Bone Marrow Transplantation I. Regeneration and Quantification of Thymocyte Progenitor Cells In the Bone Marrow

Growth kinetics of the donor-type thymus cell population after transplantation of bone marrow into irradiated syngeneic recipient mice is biphasic. During the first rapid phase of regeneration, lasting until day 19 after transplantation, the rate of development of the donor cells is independent of the number of bone marrow cells inoculated. the second slow phase is observed only when low numbers of bone marrow cells (2.5 × 10⁴) are transplanted. the decrease in the rate of development is attributed to an efflux of donor cells from the thymus because, at the same time, the first immunologically competent cells are found in spleen. After bone marrow transplantation the regeneration of thymocyte progenitor cells in the marrow is delayed when compared to regeneration of CFUs. Therefore, regenerating marrow has a greatly reduced capacity to restore the thymus cell population. One week after transplantation of 3 × 10⁶ cells, 1% of normal capacity of bone marrow is found. It is concluded that the regenerating thymus cells population after bone marrow transplantation is composed of the direct progeny of precursor cells in the inoculum.     

The relative importance of the bone marrow and spleen in the production and dissemination of B lymphocytes.

The relative importance of the bone marrow and spleen in the production of B lymphocytes was investigated in guinea pigs by the combined use of [³H]TdR radio-autography and fluorescent microscopy after the staining of B cells by FITC-F(ab′)₂-goat-anti-guinea pig Ig. Large and small lymphoid cells possess sIg in the marrow and spleen but B cell turnover in the marrow exceeds that in the spleen. That newly generated bone marrow B cells are not derived from an extramyeloid bursa equivalent was demonstrated by the absence of [³H]TdR labeled B cells in tibial marrow 72 hr after [³H]TdR was administered systemically, while the circulation to the hind limbs was occluded. Pulse and chase studies with [³H]TdR showed that large marrow B cells are derived from sIg-negative, proliferating precursors resident in the bone marrow and not from the enlargement of activated small B lymphocytes. The acquisition of [³H]TdR by splenic B cells lagged behind that observed in the marrow. Three days after topical labeling of tibial and femoral bone marrow with [³H]TdR, a substantial proportion of splenic B cells were replaced by cells that had seeded there from the labeled marrow. The studies unequivocally identify the bone marrow as the organ of primary importance in B cell generation and indicate that in the guinea pig rapidly renewed B lymphocytes of the spleen are replaced by lymphocytes recently generated in bone marrow. The rate of replacement of B lymphocytes in the lymph node by cells newly generated in the bone marrow takes place at a slower tempo than in the spleen.     

Cooperation of nonsyngeneic tolerant lymphocytes: genetic restriction.

We have used a previously devised in vivo experimental model to investigate the ability of mouse thymus-dependent (T) and bone marrow-derived (B) lymphocytes to cooperate in immune (humoral) rejection of rat Yoshida ascites sarcoma (YAS). Because of conflicting reports in the literature concerning the effectiveness of T-B cooperation across major histocompatibility complex (MHC) barriers, we explored the interaction of T and B lymphocytes from mutually tolerant animals. Tolerance was achieved by establishing radiation chimeras of B6 → B6D2F₁ and D2 → B6D2F₁ constitutions. Chimeras' erythrocytes and spleen cells were shown by serological analysis to be the donor type. When the chimera was to serve as the tumor host or B-cell source, it was thymectomized prior to irradiation and reconstitution (TIR). Tolerance was evaluated by noting the inability of chimeric spleen cells to effect graft-versus-host damage upon injection into TIR host-type mice and the markedly reduced anti-host-type reactivity in short-term [³H]thymidine-uptake tests. Successful cooperation, manifested by YAS rejection, was seen whenever donor T and host B lymphocytes were syngeneic. Parental (P) T cells enabled F₁ TIR mice to reject YAS, but the reciprocal was not true: F₁ donor T cells did not cooperate with B cells in parental TIR mice. However, when the host B lymphocytes were tolerant P cells, i.e., in a P → F₁ TIR chimera, injected F₁ T lymphocytes did cooperate successfully. The final test of allogeneic T and B cells gave the clear-cut negative answer that, even when tolerant mice are used as sources of lymphocytes, cooperation does not occur. These results therefore confirm that T and B lymphocytes must at least share one MHC haplotype in order to cooperate.     

T(Iat)- and B(Iab)-cell alloantigens determined by theH-2 linkedI region in mice

The specificity of an antiserum directed againstI region associated (Ia) antigens is described. The serum was raised in (DBA/1×B10.D2)F₁ mice against lymphocytes of AQR mice, differing from the responder for theI region only. The serum reacts with Ia antigens expressed on B cells (Iab) as well as with Ia antigens expressed on T cells (Iat). Absorption studies indicate that B cells possess at least two Ia antigens, and one of these is shared by T cells. However, this shared antigen is not present on the surface of lymphocytes of thymectomized mice. Analysis of the strain distribution of Iab and Iat antigens revealed that the Iab antigens are present on lymphocytes of mice carrying theIA ^k subregion and that the Iat antigens are present on lymphocytes of mice carryingI region genes of theH-2 ^k haplotype located between theIA andIB subregions. This conclusion is based on the analysis of the antiserum's reactivity with T and B cells of the strains B10.A(2R), B10.A(4R) and B10.HTT: the serum reacts with B and T cells of B10.A(2R) but only with B cells of B10.A(4R) mice and only weakly with T cells of B10.HTT mice.Abbreviations ALG antimouse lymphocyte globulin from rabbits - B cells bone marrow derived lymphocytes - B10 C57BL/10Sn mice - D1D2F₁ (DBA/1×B10.D2)F₁ hybrid mice - GVHR graft-vs-host reaction - Ia I region associated antigen - Iab on B cells - Iat on T cells - MLR mixed lymphocyte reaction - T cells thymus-derived lymphocytes - Thy-1 thymus antigen 1, formerly called theta - Tx-Lyc lymphocytes of thymectomized, ALG treated, lethally irradiated and anti-Thy-1 treated bone marrow reconstituted mice - 2R B10.A(2R)/SgSn mice - 4R B10.A(4R) mice     

Clonal analysis of the T lymphocytes involved in parent versus Fn1 graft-versus-host reaction

A systemic graft-versus-host reaction (GVHR) leading to 50% mortality by day 20 was elicited by the injection of CBA (10⁵) or B10 (10⁶) parental T lymphocytes into irradiated (750 rad) and bone marrow protected (CBA x B10)F₁ recipients. Between days 12 and 28 the spleens of the sick mice were analyzed by limiting dilution, performed with irradiated F₁ cells and a source of interleukin-2 (IL-2), to determine the frequency of cells with an antihost proliferative or cytolytic activity and to derive T lymphocyte clones. The frequency of cells with antihost proliferative or cytolytic activity was approximately 10^–3 in either combination. In the CBA vs F₁ GVHR, all eight clones isolated with anti-F₁ activity were Lyt-2^–, noncytolytic, mixed lymphocyte reaction (MLR) responders and IL-2 producers, three of which mapped to the A ^b locus, while in the B10 anti-F1 combination, eight of the nine anti-F₁ clones isolated were Lyt-2⁺, poor MLR responders and non-IL-2 producers, but cytolytic and mapping to K _k . These findings suggest a much higher frequency of T cells recognizing the A-locus antigens in the CBA than in the B10 strain.     

Natural resistance of irradiated 129-strain mice to bone marrow allografts: Genetic control by theH-2K region

A major genetic determinant of natural resistance to bone marrow allografts, designated asHh-3, was mapped to theH-2K region. This gene may code for or regulate the expression of cell surface structures selectively expressed on donor hemopoietic cells and recognized by naturally occurring cytotoxic effectors. Resistance was observed as failure of donor cell growth in the spleen of irradiated 129-strain (H-2 ^bc ) recipients of H-2^k bone marrow cells. The mapping was accomplished by substituting donor cells bearingk alleles throughout theH-2 complex with cells of recombinant mouse lines bearingk alleles at definedH-2 regions. The host antigraft reaction underlying resistance was abrogated by pretreating 129-strain mice with either rabbit antimouse lymphocyte serum or the antimacrophage agent silica. Grafting of H-2K^k cells into mice ancestrally unrelated to 129 but sharing theH-2 ^bc or the similarH-2 ^b haplotype, and intoH-2 ^b/k ,H-2 ^k/bc , andH-2 ^k/d F₁ hybrids revealed that resistance was unique to 129 mice, since mice of the other strains, including F₁ hybrids, were susceptible to the grafts. Thus,Hh-3 incompatibility was a necessary but insufficient condition for the manifestation of allogeneic resistance; other genetic factors not associated withH-2 conferred responder status to 129-strain mice and nonresponder status to D1.LP, B10.129(6M), B10, B6, and possibly to F₁ hybrid mice. The possible relationships between allogeneic resistance to H-2^k marrow grafts, hybrid resistance to H-2^k lymphomas, and F₁ hybrid antiparental H-2^k cytotoxicity induced in vitro are discussed.     

Bu-1 andTh-1, two loci determining surface antigens of B or T lymphocytes in the chicken

Alloantisera were prepared by reciprocal immunizations with bursal or thymic lymphoid cells between chickens of two inbred lines identical at theB major histocompatibility locus. In cytotoxic assays, antibursa sera were specific for donor-line bursa cells without absorption; antithymus sera were similarly specific for donor-line thymus cells. Both types of sera cytolyzed some peripheral lymphoid cells from spleen, bone marrow, and blood. Absorption of either type of serum with peripheral blood leukocytes removed all cytotoxic reactivity for central lymphoid cells. The inheritance of the alloantigens detected by these specific antisera was studied in F₁, F₂, and backcross progeny from the two lines. Phenotypes were determined by a method in which antisera preabsorbed with progeny leukocytes were reacted against⁵¹Cr-labeled bursal or thymic cells from chickens of both lines. The results established two independent autosomal loci-Bu-1 andTh-1-determining antigens expressed, respectively, on bursal cells and peripheral B lymphocytes or on thymic cells and peripheral T lymphocytes. Cytotoxic testing of bursal or thymic cells from chickens of other inbred lines and F₁ populations led to the tentative conclusion that the number of alleles atBu-1 is restricted, whileTh-1 exhibits considerable multiple allelism.     

A comparison of H-2 restriction of helper function using T cells from radiation chimeras and nude mice bearing thymus grafts

T cells from nude chimeras and radiation chimeras were tested for ability to cooperate with B cells of the thymus epithelium strain and B cells of the T-stem-cell strain in nude mice of appropriate strain backgrounds and also in irradiated F₁'s together with bone marrow cells of the two relevant strains (i.e., A-nu ← B or A → A × B chimera T cells were tested in A-nu and B-nu and in irradiated A × B F₁ with A bone marrow cells or B bone marrow cells). Whether the donor chimeras were antigen primed or not, all cells, when tested in nudes, provided help for the T-stem-cell type only. In contrast, in most cases, chimera T cells, tested in irradiated F₁'S, provided help for bone marrow cells of both thymus and T-stem-cell strains. These data indicate the involvement of two helper cell populations and an hypothesis to explain their interaction is presented.     

Separation of T and B lymphocytes from various mouse strains by density gradient electrophoresis

T and B mouse spleen lymphocytes were separated by density gradient electrophoresis on the basis of their surface charge. In all strains examined, the T lymphocytes were found in the high mobility fractions and the B in the low. The T and B cells were separated completely in most fractions, with some overlapping in the middle. Significant differences were found in the electrophoretic distribution profiles between the strains: C57BL/6j, C57BL/10j, (BALB/cXC57BL/6j)F₁, and all the following: B₆·C-H-2^d/cBy (congenic to C57BL/6j), BALB/c, CBA/H/T6j, C57BL/10Sn, and C3H. The C57BL/6j and the (BALB/cXC57BL/6j)F₁ cells appear more heterogeneous as far as electrophoretic mobility is concerned. Almost all the other strains give two major peaks. Moreover, the high mobility areas are less populated in the C57BL/6j and the (BALB/cXC57BL/6j)F₁ animals than in all the others. The above differences were found consistently when cells prepared by different methods were electrophoresed. It is concluded that the surface charge of lymphocytes may be genetically determined. Possible dependency on the H-2 complex or non-H-2 areas is discussed.     

B lymphocyte differentiation in lethally irradiated and reconstituted mice. I. The effect of Strontium-89 induced bone marrow aplasia on the recovery of the B cell compartment in the spleen.

The influence of ⁸⁹Sr-treatment on the recovery of the B cell compartment in lethally irradiated, fetal liver reconstituted mice was studied by means of membrane fluorescence. ⁸⁹Sr is a bone-seeking radio-isotope which causes in a dose of 3 μCi ⁸⁹Sr/g body weight a depletion of all nucleated cells, including immunoglobulin-bearing (B) cells, of the bone marrow.Treatment of irradiated and fetal liver reconstituted mice with 3 μCi ⁸⁹Sr/g body weight immediately and at 17 days after irradiation and reconstitution prevented recovery of the nucleated cell population, including B cells, in the bone marrow. In the spleen of such mice both nucleated cells and B cells reappeared at day 7 and 14 respectively. The B cell population in the spleen did not recover up to normal values during the experimental period of 45 days. It is concluded that B cell differentiation in lethally irradiated, fetal liver reconstituted mice can take place outside the bone marrow. The efficiency of this extra-medullary differentiation is discussed. The conclusion was drawn that mice with a ⁸⁹Sr-induced bone marrow aplasia are able to generate B lymphocytes. Consequently the bone marrow microenvironment seems not to be obligate to the differentiation of B lymphocytes. The peripheral lymphoid organs of such mice were found to be unable to compensate completely for the absence of B lymphocyte production in the bone marrow.     

Bone Marrow Response to Damage Induced By Hydroxyurea Or Colchicine

The extent of bone marrow damage caused by the administration of single or repeated doses of either hydroxyurea (1000 mg/kg b.w.) or colchicine (1 mg/kg b.w.) are comparable. This conclusion is based on serial studies of bone marrow cellularity and of the CFUc numbers in the bone marrow. the proliferation response of the pluripotential haemopoietic stem cells, determined by the cells forming colonies in the spleen of lethally irradiated mice (CFUs) markedly differs if the bone marrow damage is caused by hydroxyurea or colchicine. While hydroxyurea administration stimulates a large proportion of the resting G₀ cells into the cell cycle, the damage induced by colchicine is followed by only a mild increase in the CFUs proliferation rate. The seeding efficiency of the spleen colony technique has been determined after both hydroxyurea and colchicine administration. This parameter, important for the estimation of the number of the pluripotential haemopoietic stem cells in blood forming organs, is significantly affected by hydroxyurea administration, but also by repeated injections of colchicine. Following a single dose of hydroxyurea, the time-course of the CFUs numbers, which were corrected for the change in the seeding efficiency, shows an overshoot occurring after 18–20 hr. At the other time periods, the number of pluripotential haemopoietic stem cells is little affected by a single hydroxyurea injection. This poses a question about the nature of the stimulus, which after hydroxyurea administration triggers the CFUs from the resting G₀ state into the cell cycle. There is evidence that this stimulus is probably not represented by the damage caused to the various intensively proliferating cell populations of the bone marrow. This evidence is based on experiments which show that colchicine induced damage, of a degree similar to that after hydroxyurea, does not stimulate the CFUs proliferation rate to an extent comparable to hydroxyurea. The possibility that colchicine could block CFUs in the G₀ state or that it could interfere with the progress of CFUs through the G₁ and S phases of the cell cycle have been ruled out by experiments which demonstrated that colchicine (1 mg/kg b.w.), administered 10 min before hydroxyurea, does not reduce the number of CFUs triggered into the cell cycle as the consequence of hydroxyurea administration.     

Immunomodulation property of hexane fraction of leaves of Cinnamomum tamala Linn. in rats

The leaves of Cinnamomum tamala Linn. (CT) (Lauraceae) clinically used in Ayurveda as antidiabetic and diuretic, but no reports are available towards immunomodulating property. Its hexane fraction (CTH) was orally given to rats for 10 days and delayed type of hypersensitivity (DTH), antibody producton against sheep red blood cells (SRBCs), mitotic index in bone marrow cells and concanavalin A (Con A) mediated proliferation of lymphocytes were assessed. Further on 30 days treatment, change in body weight (BW), spleen weight, thymus weight, bone marrow cellularity and hematological changes were observed. It inhibited significantly the DTH response (IC₅₀ 1475 ± 57.19 mg kg^?1 BW), antibody production, suppressed mitotic index in bone marrow cells along with the suppression of lymphocyte proliferation against Con A (IC₅₀ 63.33 ± 1.95 µg mL^?1). In all experiments, cyclophasphamide and dexamethasone had been used as reference drug for in vivo and in vitro studies, respectively. On 30 days treatment, the CTH (800 mg kg^?1 BW and above) significantly suppressed growth rate, increase of spleen and thymus weight and low bone marrow cellularity. In hematological examination, it inhibited total white blood cell and lymphocytes count and increased per cent of polymorphs. Thus, it could be suggested that the fraction possesses immunosuppressive property at doses, higher than 800 mg kg^?1 BW in rats. Copyright © 2010 John Wiley & Sons, Ltd.     

In vitro alloreactivity of mouse bone marrow lymphocytes

Before characterizing alloreactive cells of the bone marrow, it was necessary to reevaluate the alloantigen response in this tissue. The results of previous studies using the parental-F₁ system in the mixed-lymphocyte reaction (MLR) are open to question because of the recently documented proliferation of F₁ stimulator cells (W. H. Adler, T.Takiguchi, B. Marsh, and R. T. Smith,J. Immunol. 105, 984, 1970; P. F. Piguet, H. K. Dewey, and P. Vassalli, J. Exp. Med. 146, 735, 1977). The culture system was optimized for measuring the MLR of bone marrow lymphocytes enriched on sucrose density gradients. The proliferative response of the enriched fraction (BML) to 2000-R irradiated allogeneic spleen cells was three times as high as the response of unfractionated bone marrow. For maximal responses, antigen concentration had to be twice as high for the BML as for the lymph node, and in a time course study the highest [³H]TdR uptake occurred on Day 3 in BML cultures and on Day 5 in the LN. In lymph node semiallogeneic cultures stimulator cell proliferation can be disregarded, while semiallogeneic BML MLR err significantly on the high side. When BML were matched with allogeneic stimulator cells at the H-2 locus, they gave good MLR responses, provided there was a minor Mls histocompatibility locus difference, while in the lymph node the response was greatly diminished in similar mixtures. The differences in the BML and lymph node alloantigen responses with respect to antigen concentration, kinetics and susceptibility to F₁ and Mls stimulation, suggest that the bone marrow alloantigen response is mediated by a cell population that is different than alloresponsive cells in the lymph node.     

Properties of Educated T Cells for Rosette Formation and Cooperation with T Cells

IT has been shown that the humoral antibody response in mice to many antigens requires cooperation between thymus derived lymphocytes (T cells) and bone marrow derived lymphocytes (B cells)^1,2. The B cells are the direct precursors of antibody secreting cells and, although T cells react specifically with antigen, their role is unknown^2–6.     

Proliferation Inhibition of Murine Pluripotent Haemopoietic Stem Cells By Interferon Or Poly I:C

The effect of mouse serum interferon (IF) in vitro and an inducer in vivo on the proliferation of a pluripotent stem cell population with high turnover rate was studied. Proliferation rate was characterized by the number of CFUs in the S phase of the cell cycle. Increased proliferation of bone marrow stem cell populations was produced either by irradiating the donor mice with 3·36 Gy (336 rad) ⁶⁰Co-gamma rays 7 days before the experiment or by incubating normal bone marrow cells with 10–11 M concentration of isoproterenol. IF considerably reduced the number of CFUs in S phase in both cases without reducing the CFUs content of the samples. Injection of IF inducer (4 mg/kg poly I:C) into regenerating mice also inhibited the proliferation of CFUs without decreasing the femoral CFUs level. Regeneration kinetics of CFUs from irradiated poly I:C-treated mice ran parallel with that of irradiated untreated animals but showed a characteristic delay corresponding to approximately one CFUs doubling. A transient, non-cytotoxic proliferation inhibitory effect of IF or IF inducer is, therefore, proposed.     

Alteration of allospecific t-cell receptors after differentiation from prethymic precursor cells in semiallogeneic environments

Murine bone marrow cells (strain A) have been allowed to differentiate in vivo in syngeneic (A) or semiallogeneic hosts (A × B) to produce mature splenic T lymphocytes. After stimulation of these cells with irradiated allogeneic (C) spleen cells in tissue cultures, the cytotoxic T-cell blasts (CTL) were purified by velocity sedimentation and used to immunize (A × C) F₁ hybrid mice, to produce antisera recognizing the receptor structure (for C) on the relevant A cytotoxic cells (and their precursors). Using these sera we have been able to show that the T-cell receptor for alloantigen C on strain A cytotoxic precursor lymphocytes (CTLp) seems to differ according to the host environment in which those T cells differentiate from immature bone marrow precursors.     

H-2 restriction specificity of T cells from H-2 incompatible radiation bone marrow chimeras: Further evidence for the absence of crucial influence of the host/thymus environment on the generation of H-2 restricted TNP-specific T lymphocyte precursors

Experiments were conducted to answer the questions related to (a) the role played by the antigen-presenting cells (APCs) present within the thymus and (b) the effect of radiation dose to the recipients on the H-2 restriction profile of TNP-specific cytotoxic T lymphocyte precursors (CTLP) recovered from spleens and/or thymuses of H-2 incompatible radiation bone marrow chimeras (BMC). The H-2 restriction profile of intrathymically differentiating TNP-specific CTLPs was also analyzed in order to test an argument that donor-H-2 restricted CTLP detected in spleens of H-2 incompatible BMC were due to the extrathymically differentiated T cells under the influence of donor-derived lymphoreticular cells. The results indicated the following: (i) splenic T cells from B10(H-2^b)→ (B10(H-2^b) → B10.BR(H-2^k)) chimeras, which were constructed by irradiating primary BIO → B10.BR chimeras with 1100 R and reconstituting them with donor-type (B10) bone marrow cells as long as 8 months after their construction, manifested restriction specificities for both donor- and host-type H-2, (ii) splenic T cells from two types of (B10 × B10.BR)F₁→ B10 chimeras which were reconstituted after exposure of the recipients with either 900 or 1100 R with donor-type bone marrow cells generated both donor- and host-H-2 restricted TNP-specific cytotoxic T cells, and (iii) the TNP-specific CTLPs present in the regenerating thymuses of B10.BR → B10 and (B10 × B10.BR)F₁→ B10 chimeras 4 weeks after their construction were also shown to manifest both donor- and host-H-2 restriction specificities. The significance of these findings on the H-2 restriction profile of CTLP generated in BMCs is discussed.     

Sialic acid: A specific role in hematopoietic spleen colony formation

Vibrio cholerae neuraminidase (VCN) treatment of donor bone marrow cells results in a reduction in the number of hematopoietic colonies (CFUs) formed in the spleens of lethally irradiated mice. Treatment of marrow cells with sodium periodate under mild conditions, known to preferentially oxidze sialic acid, also reduced CFUs while subsequent potassium borohydride reduction restored CFUs to 80% of control levels. Innoculum viability as measured by in vitro incorporation of tritiated precursors into proteins, nucleic acids, and oligosaccharides was unaffected by VCN treatment. The ability of bone marrow cells in culture to respond to the hormone erythropoietin, as measured by the incorporation of ⁵⁹Fe into cyclohexanone-extractable heme, was also not affected by neuraminidase, making a cytotoxic effect of the VCN preparation unlikely. Incubation of VCN-treated marrow with either β-galactosidase or trypsin had no effect on the VCN-induced reduction in CFUs. These results are consistent with the idea that membrane sialic acid plays a direct and specific role in the implantation and development of CFUs.