A new lymphocyte alloantigen (Ly-10) controlled by a gene linked to theLyt-1 locus

Spleen cells from a (BALB/cxC57BL/6)F₁ mouse immunized with CBA/J spleen cells were fused with the myeloma cell line NS-1. One of the six established hybrid cell lines continuously secreted antibody that recognized a new antigenic specificity, tentatively called Ly-10.1. This newly found antigen is expressed on thymocytes, on splenic T and B cells, on bone-marrow cells, and on the cells derived from brain, kidney and liver. It is also expressed on a continuous cell line, 416B, with stem-cell characteristics. The unique tissue distribution and, furthermore, a distinct strain distribution pattern distinguishes Ly-10.1 from any known murine lymphocyte alloantigen. On the basis of reactivity with cells of the C57BL/6-Lyt-1^a congenic strain, one gene governing Ly-10 expression is assigned to the Lyt-1 region of chromosome 19.We chose the notation Ly-10 rather than Ly-9 to allow for a future decision that Lgp 100 (Ledbetter et al. 1979) should be renamed Ly-9.     

A V region determinant (idiotope) expressed at high frequency in B lymphocytes is encoded by a large set of antibody structural genes.

Idiotope Ac38, a V region determinant of the lambda 1 chain-bearing, germ line encoded antibody B1-8, is expressed at high frequency (approximately 1/40) in lambda 1 chain-bearing B cells. Here, we describe the isolation of lambda-positive hybridomas from C57BL/6 mice which had been immunized with antibody Ac38, the antibody recognizing idiotope Ac38. In Northern blot analysis, mRNA isolated from 10 such hybridomas hybridizes with a cDNA probe from the VH gene expressed in the cell line B1-8. Amino acid sequence analysis of the VH regions of four of the hybridoma proteins reveals that they are all derived from related, though distinct, germ line VH genes. In one case the sequence data suggest that extensive somatic mutation has taken place. Only one of the four sequences derives from the same VH gene that is expressed in the cell line B1-8. Together with earlier evidence, the present data demonstrate that the Ac38 idiotope is a marker for at least five VH and three D region genes in the C57BL/6 germ line. This explains the high frequency at which this idiotope is expressed in the B cell population. In addition, our sequence determinations identify two VH genes in the C57BL/6 strain which are closely related (and possibly allelic) to two known BALB/c VH genes. One of these genes is the gene expressed in the BALB/c myeloma MOPC 104E.     

Expression of Ly-6 on activated T and B cells: Possible identity with Ala-1

The antigens Ala-1 and Ly-6 were first thought to be different on the grounds that Ala-1 was present only on activated T and B lymphocytes while Ly-6 was present only on post-thymic T lymphocytes. In this paper, it is shown that Ly-6 is expressed on activated B cells, including PFC and LPS blasts, and that after typing of several recombinant inbred lines,Ala-1 andLy-6 remain genetically inseparable. Based on available data, it is most likely that Ly-6 is in fact Ala-1, although further testing is required to confirm the absence of Ly-6 from nonactivated lymphocytes.Abbreviations used in this paper Con A concavalin A - LPS lipopolysaccharide - SRBC sheep red blood cells - PFC plaque-forming cells - RI recombinant inbred strains - B6 C57BL/6 mice     

Chromosomal location of the Ly-49 (A1, YE1/48) multigene family. Genetic association with the NK 1.1 antigen

The Ly-49 (A1, YE1/48) Ag is a disulfide-linked dimer with 44-kDa subunits, and is expressed on the cell surface of rare T cell tumors of C57BL/6 origin. Although this Ag is undetectable by flow microfluorimetry analysis, normal cells have been shown to express the A1 Ag by immunoprecipitation experiments performed on surface radioiodinated spleen and thymus cells. We (J. Immunol. 143:1379, 1989) and others (J. Immunol. 142:1727, 1989) have recently isolated cDNA encoding the Ly-49 Ag. Southern blots with an Ly-49 cDNA probe revealed multiple bands, consistent with cross-hybridization to other members of a multigene family, and significant RFLP between the C57BL/6 and BALB/c strains. When the RFLP patterns displayed by other common laboratory strains as well as informative recombinant inbred strains were examined, the Ly-49 gene family displayed five RFLP patterns and the entire family was found to reside on a contiguous stretch of the distal portion of mouse chromosome 6, the same region to which the NK1.1 Ag has been mapped. Although tissue distribution studies and transfection analysis ruled out the possibility that Ly-49 was identical to NK1.1 Ag, approximately 20% of NK1.1 cells isolated from normal spleen coexpressed Ly-49 and all Ly-49+ cells were CD3-. Although spleen cells cultured in high doses of rIL-2 demonstrated similar coexpression of NK1.1 and Ly-49, approximately 10% of CD3+ cells coexpressed Ly-49. The chromosomal mapping data and the expression of the Ly-49 and NK1.1 Ag suggest that the NK1.1 Ag may be a member of the Ly-49 multigene family.     

Ly-49P activates NK-mediated lysis by recognizing H-2Dd

Little is known regarding the ligand specificity of Ly-49 activating receptor subfamily members expressed by NK cells. A new Ly-49 activating receptor related to Ly-49A in its extracellular domain, designated Ly-49P, was recently cloned from 129 strain mice. We independently cloned an apparent allele of Ly-49P expressed by nonobese diabetic and nonobese diabetes-resistant mouse strain NK cells. We found it to be reactive with the A1 Ab thought to recognize a polymorphic epitope expressed only by the Ly-49A inhibitory receptor of the C57BL/6 strain. Rat RNK-16 cells transfected with Ly-49P mediated reverse Ab-dependent cellular cytotoxicity of FcR-positive target cells, indicating that Ly-49P can activate NK-mediated lysis. We determined that RNK-16 lysis of Con A blasts induced by Ly-49P was MHC dependent, resulting in efficient lysis of H-2Dd-bearing targets. We found that the Dd alpha1/alpha2 domain is required for Ly-49P-mediated RNK-16 activation, as determined by exon shuffling and transfection. Thus, Ly-49P is the second activating Ly-49 receptor demonstrated to induce NK cytotoxicity by recognizing a class I MHC molecule.     

Ly-m11: the H-3 region of mouse chromosome 2 controls a new surface alloantigen

Spleen cells from an SJL mouse immunized with B10.S spleen cells were fused with the nonsecretor myeloma line NS.1. One established hybrid cell line continuously secreted antibody that recognized a new antigenic specificity, tentatively called "Ly-m11." This newly found antigen is detectable on nearly 100 percent of spleen and lymph-node cells, 70 percent of bone-marrow cells, and 20 percent of thymus cells by direct cytotoxicity assays, and on the cells derived from kidney and liver. Strains that are Ly-m11 (+) include C57BL/6, C57BL/10J, B10.S, C57BR/cdJ, C57L/J, and C57BL/KsJ. Other mouse strains so far tested are Ly-m11 (-). The strain distribution pattern distinguished Ly-m11 from any known murine lymphocyte alloantigens, but it follows the H-3 alpha haplotype which is defined by skin transplantation. Linkage tests of nine congenic strains of H-3 and/or H-13/alpha loci and five recombinant inbred lines including CXB, BXH, AKXL, SWXL, and BXD revealed no recombinations between H-3 and Ly-m11 loci on chromosome 2. This newly discovered Ly-m11 alloantigen could itself constitute a minor histocompatibility antigen detectable by serological means.     

Zidovudine (azido dideoxythymidine) inhibits characteristic early alterations of lymphoid cell populations in retrovirus-induced murine AIDS

Using flow cytometry technology and multiparameter analyses, we report early and characteristic alterations in lymphoid cell profile in spleen and lymph nodes due to LP-BM5 retrovirus disease (murine AIDS (MAIDS)) and the effect of azido dideoxythymidine, a nucleoside inhibitor, on these changes. MAIDS has been characterized by rapid and profound lymphoproliferation accompanied by hypergammaglobulinemia and immunosuppression. As early as 2 wk postinfection, there is a selective depletion of CD8+ cells whereas the total number of CD4+ cells increases throughout the first 8 wk of infection although the frequency is relatively stable. These population changes were partially delayed by oral AZT therapy for 6 wk postinfection. Ly-6C (AL-21) is expressed on roughly 50% of CD4+ and CD8+ cells in C57BL/6 mice. In MAIDS, the residual population of CD8+ cells is primarily Ly-6C+. The CD4+ cells have a transient increase in ratio of Ly-6C+/Ly-6C- cells at 2 wk postinfection but by 6 wk are primarily Ly-6C-. There was an increase in both the total number and percentage of Mac 1+ cells and a selective depletion of certain splenic B cell subpopulations. Azido dideoxythymidine delays these early population changes.     

Embryonic stem cells derived from C57BL/6J and C57BL/6N mice

Mouse embryonic stem (ES) cells with the C57BL/6 genetic background allow the generation of knockout mice without the need to backcross to C57BL/6. However, C57BL/6 ES cells whose pluripotency after homologous recombination has been confirmed are not yet available from public cell banks. To facilitate the use of ES cells derived from C57BL/6 sublines in both biologic and medical research, we demonstrated that the use of knockout serum replacement as a medium supplement and 8-cell blastomeres as recipient embryos allowed establishment of ES cells and production of germline chimeric mice, respectively. Under effective conditions, a large number of ES cell lines were established from C57BL/6J and C57BL/6N blastocysts. The majority of ES cells in many cell lines obtained from both strains showed a normal chromosome number. Germline chimeric mice were generated from C57BL/6J and C57BL/6N ES cells. Finally, the ES cell line B6J-S1UTR, derived from C57BL/6J, was used for successful production of gene knockout mice. C57BL/6J ES (B6J-S1UTR and B6J-23UTR) and C57BL/6N ES (B6N-22UTR) cells are available from the cell bank of the BioResource Center at RIKEN Tsukuba Institute (http://www.brc.riken.jp/lab/cell/english/).     

Assignment of the Ly-6--Ril-1--Sis--H-30--Pol-5/Xmmv-72--Ins-3--Krt-1--Int-1--Gdc-1 region to mouse chromosome 15

Previous work has demonstrated linkage between Ly-6, H-30, and a locus, Ril-1, that affects susceptibility to radiation-induced leukemia. Results of preliminary linkage analyses suggested further that the cluster might be linked to Ly-11 on the proximal portion of mouse chromosome 2. Using molecular probes to examine somatic cell lines and recombinant inbred and congenic strains of mice, we have re-evaluated these linkage relationships. A cloned genomic DNA fragment derived from a retroviral site has been used to define a novel locus, Pol-5, that is tightly linked to both H-30 and Ril-1 as shown by analysis of the B6.C-H-30 ^c congenic mouse strain. Following the segregation of the Pol-5 mouse-specific DNA fragment in a series of somatic cell hybrids carrying various combinations of mouse chromosomes on a rat or Chinese hamster background mapped Pol-5 to mouse chromosome 15. During the course of these studies, restriction fragment length polymorphisms were defined associated with several loci, including Pol-5, Ly-6, Sis, Ins-3, Krt-1, Int-1, and Gdc-1. Three of these loci, Sis, Int-1, and Gdc-1, have been previously mapped to chromosome 15 by others using somatic cell hybrids or isoenzyme analyses. Following the inheritance of these eight loci in recombinant inbred strains of mice allowed the definition of a linkage group on the chromosome with the order Ly-6-Ril-1--Sis--H-30--Pol-5--Ins-3--Krt-1--Int-1--Gdc-1. Analyses of alleles inherited as passengers in B6.C-H-30 ^c, C3H.B-Ly-6 ^b, and C57BL/6By-Eh/+ congenic mouse strains and in situ hybridization experiments support the above gene order and indicate further that the cluster is located on distal chromosome 15, with Ly-6 and Sis near Eh.Abbreviations A agouti - Abl cellular homolog of the Abelson leukemia virus oncogene - Ada adenosine deaminase - Ak-1 adenylate kinase-1 - AXB A/J × C57BL/6J recombinant inbred strain - B2m beta-2 microglobulin - BXA C57BL/6J × A/J recombinant inbred strain - BXD C57BL/6J × DBA/2J recombinant inbred strain - BXH C57BL/6J × C3H/HeJ recombinant inbred strain - CXB BALB/cBy × C57BL/6By recombinant inbred strain - DNA deoxyribonucleic acid - Eh hairy ears - Fpgs folypolyglutamyl synthetase - FXI fractionated x-irradiation - Gdc-1 glycerol phosphate dehydrogenase-1 - Il2r IL-2 receptor - Ins-3 a novel insulinlike gene - Int-1 mammary tumor integration site-1 - Itp inosine triphosphatase - Krt-1 the locus designated here includes a cluster of at least three keratin genes - LTR long terminal repeat - Ly lymphocyte - Lv-6 lymphocyte antigen-6 - Ly-11 lymphocyte antigen-11 - MIH minor histocompatibility - Myc cellular homolog of the Abelson leukemia virus oncogene; pa, pallid; - Pol-5 locus encoding retroviral polymerase-5 - RFLP restriction fragment length polymorphism - RI recombinant inbred mouse strains - Ril-1 radiation-induced leukemia susceptibility-1 locus - SDP strain distribution pattern - Sis cellular homolog of the simian sarcoma virus oncogene - SFFV spleen focus-forming virus - Tpi-1 triosephosphate isomerase-1 - Ve velvet     

Investigations into the nature of Igh-V region-restricted T cell interactions by using antibodies to antigens on methylcholanthrene-induced sarcomas. I. Analysis of an Igh-V-restricted suppressor-inducer factor

We have previously demonstrated the relationship between antigens on BALB/c methylcholanthrene (MC)-induced fibrosarcomas and T cell regulatory molecules by using a variety of antisera raised to these sarcomas in BALB/c and BALB/c X C57BL/6 (CB6F1) mice. One such pool of antiserum, a CB6F1 anti-CMS 4 (Pool XIV) serum, was used to investigate the nature of the T cell regulatory structures recognized by these antibodies. Pool XIV antiserum was capable of blocking the induction of feedback suppression by Ly-1 TsiF, an SRBC-specific suppressor T cell factor secreted by Ly-1+, 2- I-J+ T cells. Ly-1 TsiF induces suppression by interacting with an Ly-1+,2+ I-J+ T cell target. Successful interaction of Ly-1 TsiF with its target cell requires genetic homology between inducer and target cells at the variable region of the immunoglobulin heavy chain gene complex (Igh-V). The addition of Pool XIV antiserum to primary in vitro anti-SRBC cultures resulted in blocking the ability of Ly-1 TsiF from Igha (BALB/c) and Ighj (CBA/J) mice to induce suppression on syngeneic cells, whereas suppression induced by Ly-1 TsiF in Ighb (B6), Ighc (DBA/2), Ighd (A/J), and Ighe (AKR) mice are unaffected by addition of the Pool XIV antiserum. The ability of Pool XIV antiserum to block Ly-1 TsiF activity is linked to the Igh region, because Pool XIV antiserum can block Ly-1 TsiF from BALB/c (H-2d, Igha) and the Igh congenic B.C9 (H-2b, Igha) while not affecting Ly-1 TsiF activity on B6 (H-2b, Ighb) or its Igh congenic C.B20 (H-2d, Ighb). In CB6F1 animals, Pool XIV antiserum could block the ability of CB6F1 Ly-1 TsiF to suppress BALB/c spleen cells but not B6 spleen cells. Conversely, Pool XIV antiserum could block the ability of BALB/c Ly-1 TsiF to suppress CB6F1 spleen cells, whereas B6 Ly-1 TsiF showed normal suppressive activity in the presence of Pool XIV antiserum. In contrast, Pool XIV was capable of blocking the ability of Ly-1 TsiF from BALB/c into CB6F1 bone marrow chimeras (BMC) to suppress both BALB/c and B6 mice, whereas the activity of Ly-1 TsiF from B6 into CB6F1 BMC on BALB/c or B6 spleen cells was unaffected by the addition of Pool XIV antiserum. We then investigated the molecular nature of the molecule recognized by Pool XIV antiserum on the Ly-1 TsiF.(ABSTRACT TRUNCATED AT 400 WORDS)     

A new erythrocytic antigen of C57BL/10 (B10) mice

A new antigen, detectable on murine erythrocytes by hemagglutination assay with a (BALB/cCrl X SWR/J)F1 anti-B10.D2n/Sn alloantiserum, is described. Among the inbred and congenic mouse strains tested for reactivity with the antiserum, only the immunizing strain, B10.D2, and its congenic resistant partner, C57BL/10 (B10), reacted. Three other C57 strains, C57BL/6J, C57BL/6By, and C57L, were negative for the antigen. F1 hybrids between B10 and BALB/c, an antigen-negative strain, were positive for the antigen indicating that its expression is dominant. Typing of 39 (BALB/c X (BALB/c X B10)F1) and 62 [BALB/c X B10)F1 X BALB/c) backcross mice revealed that a single gene controls expression of the antigen. The gene is autosomal and not linked to H-2, Ly-4, or the c (albino) or b coat color genes.     

CD73 and Ly-6A/E distinguish in vivo primed but uncommitted mouse CD4 T cells from type 1 or type 2 effector cells

Primed CD4 T cells may develop into effector T cells such as Th1 and Th2, or remain uncommitted as Th primed precursor (Thpp) cells that can subsequently differentiate into Th1 and Th2 cells. Although mouse Thpp-like cells have also been identified among spleen and particularly lymph node cells, further characterization of these cells has been difficult without a defining cell surface marker. Using Affymetrix GeneChips followed by FACS analysis, we found that in vitro-derived Thpp cells expressed CD73 but not Ly-6A/E, whereas Th1 and Th2 cells showed the reciprocal pattern. CD73+ Ly6A/E- memory CD4 T cells were identified in normal C57BL/6 mice, and the proportion of these cells was highest in lymph nodes, lower in spleens, and lowest in the lungs. These cells produced IL-2 and MIP-1alpha, but much less IL-4 and IFN-gamma than CD73- Ly6A/E+ cells. Similar results were obtained with additional Ly-6.2 mouse strains, but not Ly-6.1 strains. Restimulation of Thpp-like CD73+ Ly-6A/E- cells in Th1- or Th2-polarizing conditions induced differentiation into populations producing mainly IFN-gamma or mainly IL-4, respectively. In contrast, the effector-like CD73- Ly-6A/E+ population was more committed, and continued to produce both IL-4 and IFN-gamma in both conditions. CD73 and Ly-6A/E expression therefore identify a population of Thpp-like cells in C57BL/6 mice and at least some other Ly-6.2 mice.     

Subpopulations of mouse Lyt-2+ T cells defined by the expression of an Ly-6-linked antigen, B4B2

The production and characterization of a rat mu,kappa monoclonal anti-mouse T cell subset antibody, B4B2, is reported in this paper. B4B2 typing of lymphoid tissues of commonly used inbred mouse strains revealed two types of reactivity patterns. They can be characterized as C57BL/6-like (B6-like) or C3H/He-like (C3H-like). Among B6-like strains, B4B2 recognizes 5 to 10% of spleen cells, 30 to 50% of bone marrow cells, and less than 2 to 3% of thymocytes. In C3H-like strains, B4B2 reacts with less than 1% of spleen cells, 2 to 8% of bone marrow cells, and less than 1% of thymocytes. B4B2 recognizes a T cell subset differentiation antigen expressed by B6-like strains but not by C3H-like strains. Typing of BXH recombinant inbred strains showed linked expression of B4B2 and the Ly-6 antigen. The expression of B4B2 antigen appears to be under codominant control as the median fluorescence distribution of B4B2+ cells in C57BL/6 was approximately twice that of (C57BL/6xC3H)F1. B4B2 was shown to react with approximately 40 to 50% of Lyt-2+ T cells and less than 1% of L3T4+ T cells. No staining of resting or activated B cells by B4B2 was detected. The ratio of B4B2+:Lyt-2+ cells was similar for resting T cells and activated T cells obtained from mitogen-stimulated cultures or mixed lymphocyte cultures. In neonatal spleen, substantially more B4B2+ than Lyt-2+ cells were found. With increasing age, however, a rapid decline in B4B2+ cells and a corresponding increase of Lyt-2+ cells was observed. By approximately 1 mo of age, the relative proportion of these subsets had reversed so that Lyt-2+ cells became more numerous than B4B2+ cells.     

Loss of TNF signaling facilitates the development of a novel Ly-6C(low) macrophage population permissive for Leishmania major infection

In the absence of TNF, the normally resistant C57BL/6 (B6.WT) strain develops a fatal, progressive form of leishmaniasis after infection with Leishmania major. It is not yet understood which TNF activity or the lack thereof is responsible for the dramatic progression of leishmaniasis in TNF-negative (B6.TNF(-/-)) mice. To elucidate the underlying mechanisms resulting in the fatal outcome of L. major infection in this gene-deficient mouse strain, we analyzed the monocytic component of the inflammatory infiltrate in the draining popliteal lymph node and the site of the infection using multicolor flow cytometry. The leukocytic infiltrate within the draining lymph node and footpad of B6.TNF(-/-) mice resembled that of B6.WT mice over the first 2 wk of cutaneous L. major infection. Thereafter, the B6.TNF(-/-) mice showed an increase of CD11c(+)Ly-6C(+)CCR2(+) monocytic dendritic cells within the popliteal lymph node in comparison with B6.WT mice. This increase of inflammatory dendritic cells was paired with the accumulation of a novel CD11b(+)Ly-6C(low)CCR2(low) population that was not present in B6.WT mice. This B6.TNF(-/-)- and B6.TNFR1(-/-)-specific cell population was CD115(+)Ly-6G(-)iNOS(-), not apoptotic, and harbored large numbers of parasites.     

A new mouse cell-surface antigen (Ly-m18) defined by a monoclonal antibody

Spleen cells from C3H/An mice immunized with spleen cells of C57BL/6-H-2 ^k mice were fused with myeloma cell line NS.1. One established hybrid cell line continuously secreted antibody that recognized a new surface antigen provisionally called Ly-m18. The new alloantigen is expressed on 90 percent of thymus cells, 55 percent of spleen cells, and 45 percent of either lymphnode or bone-marrow cells. It is also expressed on cells derived from brain, kidney, and liver. Fifty percent of either peripheral T or B cells express the Ly-m18 antigen, and some tumor cell lines with T, B, pre-B or stem cell characteristics are Ly-m18 (+). The strain distribution pattern distinguishes Ly-m1 8 antigen from all other murine lymphocyte alloantigens. The typing data of two sets of CXB and AKXL recombinant inbred strains indicate that the Ly-m18 gene is linked to the Ltw-2 locus which has not yet been assigned to a chromosome.Abbreviations used in this paper RI recombinant inbred - Con-A concanavalin A - LPS lipopolysaccharide - MLR mixed lymphocyte reaction The prefix m (monoclonal) is used following a suggestion by Klein and co-workers (1979).     

Relative positioning of the T cell and B cell determinants on an immunogenic peptide: its influence on antibody response

A tryptic peptide of bovine beta-casein (amino acid residues 184-202) was used as a model antigen to investigate how the relative position of the (helper) T cell and B cell determinants on a protein antigen influences the antibody response. Immunization with the peptide elicited a considerably higher anti-peptide response in the C3H/He strain than in the C57BL/6 strain, despite the fact that the C57BL/6 T cells showed higher reactivity than the C3H/He T cells. The T cell and B cell determinants of the peptide were identified in these two strains. Each strain recognized a single B cell determinant and a single T cell determinant. In the C3H/He strain, the T and B cell determinants were located apart from one another, while the T and B cell determinants of the C57BL/6 strain were located in a region close each other. The results suggest that the level of an antibody response depends on the topological relationship of the T cell and B cell determinants on the antigen molecule.     

Characterization and differentiation of CD4-, CD8- thymocytes sorted with the Ly-24 marker

Heterogeneity within the CD4-, CD8- thymocyte population was explored by flow microfluorometry on thymocytes from 6-wk-old female C57BL/6 mice. Double negative cells were obtained by twice killing thymocytes with anti-CD4 and anti-CD8 antibodies. The resultant population lacked CD4, CD8, and Ig on cell surfaces; it contained cells bearing Ly-24 (27%), Ly-6C (6%), and Ly-5 (B220) detected by 6B2 (6%). These markers are the same as those characteristic of lpr/lpr T cells; they also are found on bone marrow cells. In order to investigate the maturational pathway of CD4-, CD8- thymocytes, such cells were cultured in vitro for 6 days with phorbol myristate acetate + calcium ionophore. There was a marked increase in cells bearing Ly-24 with time; by 6 days essentially all bore Ly-24. A lesser increase (to 15%) in 6B2 + Thy-1 positive cells was observed. Small numbers of cells bearing CD4 and/or CD8 also were found after 6 days in vitro. In additional studies, CD4-, CD8- cells were first sorted with respect to Ly-24 and then cultured with phorbol myristate acetate + calcium ionophore. Ly-24+ cells proliferated vigorously and formed clusters whereas Ly-24- cells did not. The former gave rise to large numbers of CD4+, CD8+ cells; the latter exhibited little differentiation. These studies demonstrate substantial heterogeneity within the CD4-, CD8- thymocyte population. Use of the markers Ly-24, Ly6C, and 6B2 allows a subdivision of such progenitor thymocytes. Different stages of maturation as well as possible lineages of cells may be investigated by combining such hemopoietic cell surface markers with in vitro culture.     

Genetic variation in C57BL/6 ES cell lines and genetic instability in the Bruce4 C57BL/6 ES cell line

Genetically modified mouse strains derived from embryonic stem (ES) cells are powerful tools for gene function analysis. ES cells from the C57BL/6 mouse strain are not widely used to generate mouse models despite the advantage of a defined genetic background. We assessed genetic variation in six such ES cell lines with 275 SSLP markers. Compared to C57BL/6, Bruce4 differed at 34 SSLP markers and had significant heterozygosity on three chromosomes. BL/6#3 and Dale1 ES cell lines differed at only 3 SSLP makers. The C2 and WB6d ES cell lines differed at 6 SSLP markers. It is important to compare the efficiency of producing mouse models with available C57BL/6 ES cells relative to standard 129 mouse strain ES cells. We assessed genetic stability (the tendency of cells to become aneuploid) in 110 gene-targeted ES cell clones from the most widely used C57BL/6 ES cell line, Bruce4, and 710 targeted 129 ES cell clones. Bruce4 clones were more likely to be aneuploid and unsuitable for ES cell-mouse chimera production. Despite their tendency to aneuploidy and consequent inefficiency, use of Bruce4 ES cells can be valuable for models requiring behavioral studies and other mouse models that benefit from a defined C57BL/6 background. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

B cell potential can be obtained from pre-circulatory yolk sac, but with low frequency

The ontogenic source of definitive hematopoietic system has been identified in non-mammalian vertebrates such as birds and amphibians by orthotopic embryo grafting, but remains unclear for mammals because of technical difficulties. Here, we successfully generated mouse chimeras by grafting yolk sac (YS) on YS of the host embryos before establishing circulation between YS and embryo proper and cultured the whole embryo for 66 h. Donor YS were isolated from C57BL/6 Ly-5.1 and EGFP-transgenic mouse embryos, and recipient embryos from C57BL/6 Ly-5.2 mouse. Almost one-half of the grafts in YS-YS chimeras survived and had obvious blood flow; graft-derived cells comprised 12.7+/-0.9% of the blood cells in the circulation. These graft-derived blood cells consisted mainly of erythroid cells, some myeloid cells and a few blastic cells. In addition, CD19(+) B cells were generated from the graft-derived cells isolated from aorta-gonad-mesonephros (AGM) regions of the YS-YS chimeras; however, the frequency of the YS-derived B cell was low (1.0+/-0.6%) when co-cultured with OP9 stromal cells. These results demonstrate that B cell potential exists in YS before the circulation. Although the major source for B cell is intra-embryonic AGM region, YS may contribute to definitive lymphopoiesis in vivo in mice.     

Mouse serum amyloid P-component (SAP) levels controlled by a locus on chromosome 1

Recombinant inbred strains were used to demonstrate the existence of a major locus on chromosome 1, designated Sap, which controls the endogenous concentration of the mouse acute phase reactant, serum amyloid P-component (SAP). Levels of SAP were associated with alleles at the Ly-9 locus in two sets of RI strains: BXD (C57BL/6J × DBA/2) and BXH (C57BL/6J × C3H/HeJ). Low endogenous levels of SAP were present in the C57BL/6J progenitor strain and in most of the RI strains which inherited the Ly-9 ^ballele. High levels of SAP were present in the DBA/2J and C3H/HeJ progenitors and in most of the RI strains which inherited the Ly-9 ^aallele. In the BXD strains 91% of the genetic variation of SAP levels was accounted for by segregation at the Ly-9 locus while an additional 9% was attributed to genetic factors unlinked to Ly-9. In the BXH strains the percentage of genetic variation accounted for by Ly-9 segregation was reduced to 46%, while 54% was accounted for by other genetic factors. Because of background genetic variation it was not possible to detect any crossovers between Sap and Ly-9. However, in the BXD strains the linkage between Sap and Ly-9 appears to be quite close. The B6.C-H-25 ^ccongenic strain, which carries a segment of BALB/c chromosome 1 including the minor histocompatibility locus H-25 on a C57BL/6By background, had the same endogenous SAP level as the BALB/c donor strain.