Mechanisms of killing of measles virus-infected cells by human lymphocytes: interferon associated and unassociated cell-mediated cytotoxicity

The recent interest in natural killer (NK) cells in immunosurveillance and the ability of infection with certain organisms to modulate NK activity led us to examine the influence of Toxoplasma gondii infection on mouse NK cells. Infection of BALB/c mice with 5 × 10³ virulent Toxoplasma intraperitoneally (ip) resulted in significantly enhanced NK activity in peritoneal exudate cells (PC) and in spleen cells (SC). Intravenous (iv) and subcutaneous (sc) challenge of BALB/c mice with Toxoplasma also resulted in enhanced natural killer (NK) activity in PC and SC. In BALB/c mice, as well as in other strains (A/J, C57BL/6, C3H/HeJ, CeH/HeN, [A/J × C3H]F₁), peak augmentation of PC and SC NK activity was observed 3 days following ip Toxoplasma challenge. Administration of silica to mice abolished Toxoplasma-induced NK cytotoxicity. BALB/c mice chronically infected with Toxoplasma had significantly higher endogenous NK activity than did controls in PC but not in SC. Chronically infected BALB/c mice boosted with virulent Toxoplasma ip exhibited significantly enhanced NK activity in PC but not in SC. Thus, acute and chronic infection with Toxoplasma modulates NK activity in addition to macrophage activation and thereby provides a system that should facilitate study of the relative contribution of NK cells and activated macrophages in resistance to tumor growth and spread.     

Murine responses to (Tyr-Glu-Ala-Gly)n: II. H-2 and non-H-2 gene effects

Mice of the H-2^b haplotype responded to the sequential polymer poly(Tyr-Glu-Ala-Gly) in the in vitro T-cell proliferative assay, irrespective of whether they were homozygous or heterozygous at the H-2^b locus. The antibody responses of the H-2^b congenic mice to this polymer were variable, with A.BY and BALB.B showing responses better than those of C57BL/6 and C57BL/10 strains. The antibody responses of the F₁ progeny of (responder × nonresponder) strains of mice to this polymer are generally lower than the responder parents. F₁ mice with C57BL/10 background were the poorest responders. Studies with F₂ mice and backcross progenies of selective breeding of high and low antibody responder (C57BL/6 × BALB/c) F₁ to high responder C57BL/6 mice indicated that both non-H-2 genes and H-2 gene dosage effects influenced the magnitude of the humoral antibody responses. Animals having low responder non-H-2 background and only half the dosage of the responder immune response genes has greatly diminished antibody responses.     

Comparison of patterns of hybrid resistance to the BALB/c plasmacytomas LPC-1 and MPC-11

Summary Patterns of genetic control of hybrid resistance to the BALB/c plasmacytoma LPC-1 were studied for comparison with those to MPC-11, a plasmacytoma investigated previously. The overall patterns of hybrid resistance to the two tumors were similar, i.e., hybrids between BALB/c and BALB congenic resistant (CR) strains, A and A CR strains, SJL and DBA/2 were as susceptible to LPC-1 as BALB/c mice themselves, whereas hybrids between BALB/c and AKR, C57BL/Ks, DBA/1, C57BL/6 (B6), C57BL/10 (B10) and B10 CR strains were resistant to LPC-1 as previously shown with MPC-11. Heterozygosity within the H-2 complex alone was insufficient for resistance to either tumor. Among hybrids between BALB/c and the B10 CR strains, however, the presence of certain H-2 haplotypes influenced the degree of resistance seen and this H-2 effect was different for the two tumors. A sex effect on resistance to LPC-1, but not to MPC-11, was seen among F₁ hybrids between BALB/c and DBA/1 although not in any other F₁ hybrids. Among ((B10×BALB/c)F₁×BALB/c) and (BALB/c×(B10×BALB/c)F₁) and ((BALB/c×B10)F₁×BALB/c) and ((BALB/c×B10)F₁×BALB/c) backcross mice, however, significantly more males than females were resistant to LPC-1 and the results of this study are compatible with the idea that in F₁ hybrids between BALB/c and B10, resistance to LPC-1 is controlled by two dominant autosomal genes, one of which is sex-limited and neither of which is linked to H-2. In contrast, hybrid resistance to MPC-11 in this cross is controlled by a single gene. Cross-protection experiments indicated that the two tumors share at least one tumor-associated transplantation antigen.     

Xenogeneic antisera against T-lymphocyte receptors recognizing allogeneic transplantation antigens: Preparation and properties

Antireceptor sera ARS-1 (anti-CBA-anti-C57BL/6) and ARS-2 (anti-C57BL/6-anti-BALB/c) were prepared in a xenogeneic system by immunizing rabbits with alloimmune CBA anti-C57BL/6 and C57BL/6 anti-BALB/c lymphocytes and subsequent exhaustive absorption of rabbit immune sera with red blood cells, lymphocytes, liver cells, and serum from intact mice. In the cytotoxicity test, both ARS sera lysed only activated T lymphocytes of corresponding, but no other specificities, and did not affect intact lymphocytes. They did not inactivate in vitro the PFC-producing antibodies to SRBC or inhibit the immune response to SRBC and Viantigen of Salmonella typhi in adoptive transfer experiments. Pretreatment of intact CBA lymphocytes in vitro with ARS-1 plus complement suppressed their ability to induce lethal GvH disease in irradiated (CBA × C57BL/6)F₁, but not (CBA × BALB/c)F₁ recipients; similar pretreatment of C57BL/6 lymphocytes did not lower lethality among irradiated (CBA × C57BL/6)F₁ recipients. This method of preparing ARS may help to obtain highly specific antireceptor sera for regulation of the immune response to different antigens in outbred animals and in humans.     

Immunosuppressive activity of murine newborn spleen cells. I. Selective inhibition of in vitro lymphocyte activation.

Cell-mediated immune responses to newborn lymphocyte alloantigens were investiated using mitogen activation, mixed lymphocyte reaction (MLR) and cell-mediated lympholysis (CML). Spleen cells from 1- to 5-day-old (C57BL/6 × Balb/c) F₁ mice co-cultured with maternal strain (BALB/c) splenocytes did not affect DNA synthesis of maternal strain cells in the presence of concanavalin A or phytohemagglutinin. Newborn cells did inhibit the lipopolysaccharide response of maternal strain lymphocytes and these cells also depressed DNA synthesis when added to MLR cultures of BALB/c and C57BL/6 spleen cells. Newborn cells expressed poor stimulatory capacity in semiallogeneic MLR and also caused marked inhibition of DNA synthesis when added to semiallogeneic MLR containing BALB/c (responder) and CB6F₁ adult splenocytes (stimulator). The suppression of MLR by neonatal cells persisted for the first 2 weeks of life and was associated with a soluble factor released during culture. The suppressive activity was almost completely abrogated after depleting the T-cells from newborn splenocytes. However, these same cells did not interfere with the in vitro generation of cytotoxic lymphocytes in the CML assay. The selective immunosuppressive properties of newborn spleen cells may be important during pregancy by protecting the immunologically alien fetus from rejection by the mother.     

Regulatory T cells enhance susceptibility to experimental trypanosoma congolense infection independent of mouse genetic background

Background

BALB/c mice are highly susceptible while C57BL/6 are relatively resistant to experimental Trypanosoma congolense infection. Although regulatory T cells (Tregs) have been shown to regulate the pathogenesis of experimental T. congolense infection, their exact role remains controversial. We wished to determine whether Tregs contribute to distinct phenotypic outcomes in BALB/c and C57BL/6 mice and if so how they operate with respect to control of parasitemia and production of disease-exacerbating proinflammatory cytokines.

Methodology/Findings

BALB/c and C57BL/6 mice were infected intraperitoneally (i.p) with 10³ T. congolense clone TC13 and both the kinetics of Tregs expansion and intracellular cytokine profiles in the spleens and livers were monitored directly ex vivo by flow cytometry. In some experiments, mice were injected with anti-CD25 mAb prior or post T. congolense infection or adoptively (by intravenous route) given highly enriched naïve CD25⁺ T lymphocytes prior to T. congolense infection and the inflammatory cytokine/chemokine levels and survival were monitored. In contrast to a transient and non significant increase in the percentages and absolute numbers of CD4⁺CD25⁺Foxp3⁺ T cells (Tregs) in C57BL/6 mouse spleens and livers, a significant increase in the percentage and absolute numbers of Tregs was observed in spleens of infected BALB/c mice. Ablation or increasing the number of CD25⁺ cells in the relatively resistant C57BL/6 mice by anti-CD25 mAb treatment or by adoptive transfer of CD25⁺ T cells, respectively, ameliorates or exacerbates parasitemia and production of proinflammatory cytokines.

Conclusion

Collectively, our results show that regulatory T cells contribute to susceptibility in experimental murine trypanosomiasis in both the highly susceptible BALB/c and relatively resistant C57BL/6 mice.     

Analysis of subpopulations of glass-adherent mouse skin cells controlling resistance/susceptibility to infection with Leishmania tropica,and correlation with the development of independent proliferative signals to Lyt-1+/Lyt-2+ T lymphocytes

A comparison has been made between the course of Leishmania tropica infection of BALB/ c, CBA, and (BALB/c × CBA)F₁ mice in vivo and the growth of the parasite in isolated adherent skin cells in vitro. The susceptible phenotype of the BALB/c mouse was reflected in an innate susceptibility of a discrete subpopulation of adherent skin cells to permit extensive and prolonged growth and replication of the parasite in tissue culture. When cells infected in culture were used to stimulate proliferation of immune lymphocytes from “cured” mice, the skin cells of susceptible BALB/c mice were deficient in their ability to induce proliferation of lymphocytes of BALB/c, CBA, or BCF₁ origin (all immunized in the appropriate bone marrow reconstituted irradiated BCF₁ hosts). In contrast, these skin cells were able to induce proliferation of immune lymphocytes if the L. tropica antigen source used was a soluble excreted extract (EF), rather than that produced by a live parasite infection. Stimulation of naive lymphocytes using an infected adherent skin cell population from BALB/c mice was found to produce a cell population(s) (Thy-1.2⁺, Lyt-2⁺ and including some Lyt-1⁺ cells) able to inhibit subsequent sensitization of normal BCF₁ lymph node cells by L. tropica antigens. The susceptibility of the BALB/c mouse in vivo thus may be attributable to the early contact of T-lymphocyte subsets in BALB/c mice with the high-antigen load maintained in this discrete skin cell population. These particular skin cells were also found to express low levels of Ia antigens.     

Experimental Murine Fascioliasis Derives Early Immune Suppression with Increased Levels of TGF-�� and IL-4

In fascioliasis, T-helper 2 (Th2) responses predominate, while little is known regarding early immune phenomenon. We herein analyzed early immunophenotype changes of BALB/c, C57BL/6, and C3H/He mice experimentally infected with 5 Fasciola hepatica metacercariae. A remarkable expansion of CD19⁺ B cells was observed as early as week 1 post-infection while CD4⁺/CD8⁺ T cells were down-regulated. Accumulation of Mac1⁺ cells with time after infection correlated well with splenomegaly of all mice strains tested. The expression of tumor necrosis factor (TNF)-α mRNA in splenocytes significantly decreased while that of IL-4 up-regulated. IL-1β expression was down-modulated in BALB/c and C57BL/6 mice, but not in C3H/He. Serum levels of transforming growth factor (TGF)-β were considerably elevated in all mice during 3 weeks of infection period. These collective results suggest that experimental murine fascioliasis might derive immune suppression with elevated levels of TGF-β and IL-4 during the early stages of infection.     

Foxp3+ Regulatory T Cells Delay Expulsion of Intestinal Nematodes by Suppression of IL-9-Driven Mast Cell Activation in BALB/c but Not in C57BL/6 Mice

Accumulating evidence suggests that IL-9-mediated immunity plays a fundamental role in control of intestinal nematode infection. Here we report a different impact of Foxp3⁺ regulatory T cells (Treg) in nematode-induced evasion of IL-9-mediated immunity in BALB/c and C57BL/6 mice. Infection with Strongyloides ratti induced Treg expansion with similar kinetics and phenotype in both strains. Strikingly, Treg depletion reduced parasite burden selectively in BALB/c but not in C57BL/6 mice. Treg function was apparent in both strains as Treg depletion increased nematode-specific humoral and cellular Th2 response in BALB/c and C57BL/6 mice to the same extent. Improved resistance in Treg-depleted BALB/c mice was accompanied by increased production of IL-9 and accelerated degranulation of mast cells. In contrast, IL-9 production was not significantly elevated and kinetics of mast cell degranulation were unaffected by Treg depletion in C57BL/6 mice. By in vivo neutralization, we demonstrate that increased IL-9 production during the first days of infection caused accelerated mast cell degranulation and rapid expulsion of S. ratti adults from the small intestine of Treg-depleted BALB/c mice. In genetically mast cell-deficient (Cpa3-Cre) BALB/c mice, Treg depletion still resulted in increased IL-9 production but resistance to S. ratti infection was lost, suggesting that IL-9-driven mast cell activation mediated accelerated expulsion of S. ratti in Treg-depleted BALB/c mice. This IL-9-driven mast cell degranulation is a central mechanism of S. ratti expulsion in both, BALB/c and C57BL/6 mice, because IL-9 injection reduced and IL-9 neutralization increased parasite burden in the presence of Treg in both strains. Therefore our results suggest that Foxp3⁺ Treg suppress sufficient IL-9 production for subsequent mast cell degranulation during S. ratti infection in a non-redundant manner in BALB/c mice, whereas additional regulatory pathways are functional in Treg-depleted C57BL/6 mice.     

Teratocarcinoma transplantation rejection loci: AnH-2-linked tumor rejection locus

Embryoid bodies (ascites tumor) from a 129/Sv transplantable teratocarcinoma produce tumors (100%) in syngenic 129/Sv mice but fail to form tumors (3–6%) in BALB/c mice, C3H/He mice and C57BL/6 mice, in spite of the fact that the malignant stem cells of this tumor do not express detectable H-2 antigens. The available evidence indicates that this allogeneic tumor restriction has an immunological basis; 100% of the F₁ hybrid mice between 129/Sv and the three other inbred mouse strains accept the 129/Sv teratocarcinoma. The backcross and F₂ mice segregate the BALB/c, C3H/He and C57BL/6 tumor transplantation rejection loci in a manner that indicates that each of these inbred strains of mice contain one to two major transplantation rejection loci. A linkage analysis in the BALB/c and C3H/He backcross and F₂ generations indicates that these mice have a teratocarcinoma transplantation rejection locus on chromosome 17, about eight to nine recombination units from theH- 2 complex. An F₁ complementation analysis between allogeneic mice that each reject teratocarcinomas tumors (BALB/c × C57BL/6 and C3H/He × C57BL/6), indicates that the C57BL/6 mice have the 129/Sv tumor-accepting (sensitive) allele at theH-2-linked locus but reject teratocarcinomas because of antigenic differences at a second locus.While these major teratocarcinoma transplantation rejection loci determine the acceptance or rejection of a tumor by a mouse injected with high doses of tumor tissue (750 g of tumor protein), evidence is presented for a number of minor genetic factors that can (1) affect the efficiency of tumor rejection and (2) cause complete tumor rejection at lower tumor doses (7.5–75 g of tumor protein).     

DonorIgh-linked genetic control of allotype-specific antibody response

Immunogenicity of allogeneic immunoglobulins in mice were studied, measuring the allotype-specific antibody activity by agglutination of allogeneic antibody-coated red blood cells. It was found that the serum from C.B-20 mice (Igh ^b , BALB/c-congenic) was uniquely immunogenic in BALB/c mice for allotype antibody response. Whereas the C57BL/6 (Igh ^b ) serum was immunogenic only when heat aggregated and/or combined with adjuvant, the ultracentrifugation-deaggregated C.B-20 serum was definitely immunogenic when administered in a moderate dose (100 μl/mouse). Even more surprising was the fast that very low doses (0.01–0.1 μl) of soluble C.B-20 serum, but not C57BL/6 serum, down regulated the allotype-specific response effectively. Genetic analysis on congenic mice suggested that the immunogenicity is controlled by donorIgh orIgh-V(Id-C.B) inasmuch as the serum from BALB/c-congenic C.B-20 (Igh-V ^b C ^b ), but not BALB/c-congenic BAB/14 (Igh-V ^a C ^b ), mice was active in BALB/c mice in soluble form. Further studies showed that the Id-C.B was dominantly expressed on the immunoglobulins of (BALB/c×C.B-20)F₁ and (C56BL/6×C.B-20)F₁ strains, and was originally derived from the C57BL/Ka strain. The major determinant for the antibody production was encoded inIgh-C, but not inIgh-V. It is suggested thatId-C.B controls the allotype-specific antibody response in an unusual manner, possibly acting as a unique determinant activating helper T cells.     

Surface immunoglobulin of mouse thymus cells and its in vitro biosynthesis

Surface immunoglobulin (Ig) was demonstrated on thymocytes from BALB/c and CS7BL mice by lactoperoxidase radioiodination of the cells. Active synthesis of Ig in these cells was demonstrated in short-term tissue culture using ¹⁴C-labeled amino acids. The demonstration of intracellular and surface Ig required procedures that minimize proteolytic degradation.Monomeric α chains and light chains were found in the cytoplasm and on the surface of BALB/c thymocytes, whereas monomeric μ chains and light chains in the cytoplasm and on the surface of CS7BL thymocytes. Cytotoxic tests with an alloantiserum revealed that in the thymus of BALB/c mice the IgA monomeric subunits are synthesized by the θ⁺ cells.     

Analysis of the Dynamics of Infiltrating CD4+ T Cell Subsets in the Heart during Experimental Trypanosoma cruzi Infection

Chagas disease, caused by the protozoan parasite Trypanosoma cruzi, affects several million people in Latin America. Myocarditis, observed during both the acute and chronic phases of the disease, is characterized by an inflammatory mononuclear cell infiltrate that includes CD4⁺ T cells. It is known that Th1 cytokines help to control infection. The role that T_reg and Th17 cells may play in disease outcome, however, has not been completely elucidated. We performed a comparative study of the dynamics of CD4⁺ T cell subsets after infection with the T. cruzi Y strain during both the acute and chronic phases of the disease using susceptible BALB/c and non-susceptible C57BL/6 mice infected with high or low parasite inocula. During the acute phase, infected C57BL/6 mice showed high levels of CD4⁺ T cell infiltration and expression of Th1 cytokines in the heart associated with the presence of T_reg cells. In contrast, infected BALB/c mice had a high heart parasite burden, low heart CD4⁺ T cell infiltration and low levels of Th1 and inflammatory cytokines, but with an increased presence of Th17 cells. Moreover, an increase in the expression of IL-6 in susceptible mice was associated with lethality upon infection with a high parasite load. Chronically infected BALB/c mice continued to present higher parasite burdens than C57BL/6 mice and also higher levels of IFN-γ, TNF, IL-10 and TGF-β. Thus, the regulation of the Th1 response by T_reg cells in the acute phase may play a protective role in non-susceptible mice irrespective of parasite numbers. On the other hand, Th17 cells may protect susceptible mice at low levels of infection, but could, in association with IL-6, be pathogenic at high parasite loads.     

Natural regulatory T cells mediate the development of cerebral malaria by modifying the pro-inflammatory response

Cerebral malaria (CM) is a severe neurologic complication that arises predominantly in children and non-immune adults infected with Plasmodium falciparum. In the current study, the dynamics of CD4⁺CD25⁺Foxp3⁺ regulatory T cells (Tregs) and pro- and anti-inflammatory cytokines were analyzed in P. berghei ANKA (P.bANKA)-infected C57BL/6, BALB/c, and DBA/2 mice. We showed that C57BL/6 mice were susceptible to CM, while BALB/c and DBA/2 mice were resistant to CM and succumbed to hyperparasitemia and severe anemia. The proportion and absolute numbers of Tregs in BALB/c and DBA/2 mice were significantly higher than in C57BL/6 mice. The levels of pro-inflammatory cytokines, such as IFN-γ, TNF-α, IL-6, IL-17 and NO in CM-susceptible C57BL/6 mice were obviously higher than in CM-resistant BALB/c and DBA/2 mice, while the level of the anti-inflammatory cytokine IL-10 was the opposite to that of pro-inflammatory cytokines, confirming that an appropriate balance between pro- and anti-inflammatory immune responses is essential to control the pathogenesis of severe malaria, and Tregs are important regulators if this balance is to be maintained. In vivo depletion of Tregs significantly protected C57BL/6 mice from experimental CM and the production of pro- and anti-inflammatory cytokines was reversed, indicating that this cell population contributes to pathogenesis by modulating the balance of pro- and anti-inflammatory responses. Our data demonstrate that Tregs mediate the incidence and outcome of CM in P.bANKA-infected mice by modifying the pro-inflammatory response.     

Interaction of thymus lymphocytes with histoincompatible cells. IV. Mixed lymphocyte reactions of activated thymus lymphocytes

CS7BL-activated CBA T cells (T.TDL) were obtained by thoracic duct cannulation of (CBA × C57BL)F₁ mice 4 days after heavy irradiation and injection of CBA thymus cells. T.TDL behaved differently from the TDL of normal CBA mice in unidirectional mixed lymphocyte culture in a number of respects: (a) the response of T.TDL was directed specifically against C57BL antigens, whereas normal TDL responded to both C57BL and BALB/c antigens; (b) the response of T.TDL was rapid but transient compared to that of TDL; (c) whereas only approximately 3% of TDL synthesized DNA specifically in response to C57BL antigens, as many as 25% of C57BL-activated T.TDL responded to these antigens. Evidence is presented which suggests that the T.TDL have a very limited capacity to proliferate. Most of the cells which responded to antigen synthesized DNA without subsequently entering mitosis.     

Trypanosoma brucei: influence of host strain and parasite antigenic type on infections in mice

Inbred mice were infected with cloned populations of Trypanosoma brucei brucei Lister S42 under carefully controlled conditions. The course of infection was found to depend both on host strain and the antigenic type of the infecting organisms. The two antigenic types used, “NIM2” and “NIM6” had differing virulence for (CBA/H × C57BL/6)F₁ mice, and when mice were infected with parasites of one clone, trypanosomes of the other type frequently appeared after the initial population had been eliminated. Different mouse strains had varying susceptibility to clone NIM6. In most cases there was an inverse relation between the survival time and the parasite load during the first peak of parasitemia. The differences in resistance to T. brucei were unrelated to H-2 haplotype: C57BL/6 and (CBA/H × C57BL/6)F₁ were most resistant, CBA/H, BALB/c and DBA/2 less so, and C3H/He most susceptible.     

In vitro elicitation of cytotoxic response against a nonimmunogenic murine tumor by allosensitization

Summary The murine lymphoma (thymoma) PIR-2 of C57BL/6 origin, primarily induced in our laboratory by fractionated X-ray irradiation, has been shown to be nonimmunogenic by its failure to immunize syngeneic mice in vivo or to evoke a cytotoxic response in primary mixed lymphocyte-tumor cell cultures (MLTC) in vitro. We were able, however, to demonstrate the existence of anti-PIR-2 cytotoxic cells among allogeneic-primed C57BL/6 responding lymphocytes using the technique of limiting dilution cultures (LDC). The frequency of anti-PIR-2 cytotoxic cells among C57BL/6 lymphocytes sensitized against BALB/c splenocytes in mixed leukocyte culture (MLC) was 1/20 to 1/40, and the cytotoxic activity of positive LDC wells against PIR-2 reached 60% as determined by a 4-h ⁵¹Cr-release assay. The frequency of anti-PIR-2 cytotoxic cells could be increased two- to 10-fold (up to 1/4) by removing nylon-wool-adherent cells from the primed cell population and/or by enriching the primed lymphoblast population on a Percoll density gradient. Anti-PIR-2 cytotoxic cells were found to be Thy1⁺; Lytl^–2⁺ cells. Clones isolated from the LDC wells manifested strong cytotoxic activity toward PIR-2 cells and the stimulating BALB/c splenocytes but not against other H-2^b tumor lines or C57BL/6 splenocytes. We suggest that the procedure of allostimulation in MLC-LDC is an effective in vitro means of generating highly reactive cytotoxic cells against poorly immunogenic neoplasms.     

Enduring allogeneic marrow engraftment via nonspecific bone-marrow-derived regulating factors (MRF)

An ultrafiltration fraction of MW > 100,000 separated from the original medium in which bone marrow had been suspended (supernatant) stimulated incorporation of [³H]thymidine by marrow in vitro and was designated marrow regulating factor (MRF). The administration of MRF to F₁ hybrid mice transplanted with parental bone marrow resulted in lasting chimerism of the surviving mice. A few of the hybrids receiving parental marrow but no MRF survived: however, none were chimeric. Administration of MRF after irradiation in C57BL/ 6 mice transplanted with bone marrow from DBA/2 and BALB/c donors resulted in endogenous reconstitution. However, administration of MRF before (preconditioning) and again after irradiation resulted in survival of the majority of mice. These C57BL/6 mice were chimeras of DBA/2 or BALB/c marrow but showed no sign of secondary disease. Thus the use of MRF abrogates resistance to and promotes engraftment of foreign marrow and enduring chimerism when the recipients (F₁ hybrids) appear to be nonreactive to the donor (parental marrow) and also when alloreactivity is bidirectional (allogeneic combinations).     

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.     

Comparison of the ease of tolerance induction in thymus and bone marrow of three strains of mice

Three strains of mice which vary in their susceptibility to induction of immune tolerance with human gamma-globulin were studied to evaluate the cellular basis for their sensitivity to induction of the unresponsive state. Tolerance induction in BALB/c mice was difficult to establish, while tolerance induction was easily achieved in C57BL/6 and CBF₁ (BALB/c × C57BL/6) mice. The degree of unresponsiveness obtained with various tolerogen doses in intact C57BL/6 and CBF₁ mice was reflected in the sensitivity of their thymocytes to the production of the unresponsive state. In the BALB/c mouse strain slight immune suppression observed at low tolerogen doses was correlated with bone marrow cell unresponsiveness while significant levels of tolerance observed at a high tolerogen dose was due to suppression of thymus cells. It was apparent that CBF₁ mice had inherited both thymus cells and bone marrow cells which exhibited the sensitivity to induction of immune tolerance characteristic of those same cells of their C57BL/6 parent.