IA mutant functional antigen-presenting cell lines

We describe a protocol for the selection of mutant cells with an altered pattern of Ia antigenic determinants and antigen-presenting properties from a homogeneous population of functional antigen-presenting cells (APC). The APC line used in this work was obtained by fusing lipopolysaccharide-stimulated B cells from (BALB/c x A/J)F1 donors with cells from the M12.4.1 BALB/c B lymphoma cell line. The resulting hybridomas, including TA3, retained the potent antigen-presenting activity of the parental B lymphoma line and expressed Ia antigens and immune response gene-determined antigen-presenting properties of the A/J type. Mutants of TA3 were obtained by subjecting the cells to negative immunoselection with one monoclonal anti-(alpha) 1-Ak antibody and complement followed by positive immunoselection via electronic cell sorting with a second monoclonal alpha I-Ak or alpha I-Ek antibody. Two types of mutants were obtained. One, A8, appeared to have undergone a fairly limited alteration, since it lost only some of the I-Ak antigenic determinants; the second type appeared to have lost the entire I-Ak molecule but to have retained the I-E molecule. Functional studies with the A8 mutant demonstrated that the loss of a limited number of I-Ak determinants correlated with the loss of a specific I-Ak-encoded restriction element, since A8 failed to present a specific antigen, hen egg lysozyme (HEL), to a HEL-specific I-Ak-restricted T cell hybridoma but retained some capacity to present a second antigen, poly(Glu60Ala30Tyr10) (GAT), to a GAT-specific I-Ak-restricted T cell hybridoma. These results indicate that Ia antigens are the products of immune response gene loci. The availability of such mutants should allow an examination of the relationship between the structure of an Ia molecule and the antigens with which it is co-recognized by T cells.

IA mutant functional antigen-presenting cell lines

We describe a protocol for the selection of mutant cells with an altered pattern of Ia antigenic determinants and antigen-presenting properties from a homogeneous population of functional antigen-presenting cells (APC). The APC line used in this work was obtained by fusing lipopolysaccharide-stimulated B cells from (BALB/c x A/J)F1 donors with cells from the M12.4.1 BALB/c B lymphoma cell line. The resulting hybridomas, including TA3, retained the potent antigen-presenting activity of the parental B lymphoma line and expressed Ia antigens and immune response gene-determined antigen-presenting properties of the A/J type. Mutants of TA3 were obtained by subjecting the cells to negative immunoselection with one monoclonal anti-(alpha) 1-Ak antibody and complement followed by positive immunoselection via electronic cell sorting with a second monoclonal alpha I-Ak or alpha I-Ek antibody. Two types of mutants were obtained. One, A8, appeared to have undergone a fairly limited alteration, since it lost only some of the I-Ak antigenic determinants; the second type appeared to have lost the entire I-Ak molecule but to have retained the I-E molecule. Functional studies with the A8 mutant demonstrated that the loss of a limited number of I-Ak determinants correlated with the loss of a specific I-Ak-encoded restriction element, since A8 failed to present a specific antigen, hen egg lysozyme (HEL), to a HEL-specific I-Ak-restricted T cell hybridoma but retained some capacity to present a second antigen, poly(Glu60Ala30Tyr10) (GAT), to a GAT-specific I-Ak-restricted T cell hybridoma. These results indicate that Ia antigens are the products of immune response gene loci. The availability of such mutants should allow an examination of the relationship between the structure of an Ia molecule and the antigens with which it is co-recognized by T cells.

Phenotypic characterization of early events of thymus repopulation in radiation bone marrow chimeras

The phenotype of murine thymocytes repopulating the thymus of radiation bone marrow chimeras shortly after irradiation and bone marrow reconstitution was analyzed by immunofluorescence and flow microfluorometry. Thymuses in these chimeras, while essentially devoid of lymphoid cells at day 7, were repopulated by days 10 to 12 after irradiation. It was found that this initial repopulation arose from a radioresistant intrathymic precursor that expanded to an almost complete complement of host-type thymocytes. However, these host-derived thymocytes were unusual in that they were relatively deficient in Lyt 1+2- and peanut agglutinin "dull" cells as compared with normal thymocytes. Donor bone-marrow-derived cells first appeared in the irradiated chimeric thymuses between days 12 and 15 after irradiation and bone marrow transfer. By day 19, chimeric thymuses contained more than 98% donor cells. This course was identical for three chimeric combinations, each made across different genetic barriers. In contrast to the cells that populate the fetal thymus during normal ontogeny, the first donor bone-marrow-derived cells that can be detected within the irradiated chimeric thymuses already expressed phenotypically normal adult T cell subpopulations in that they contained significant numbers both of Lyt 1+2- and of Lyt 1+2+ thymocytes. Thus, the Lyt phenotype of donor cells that initially repopulate an adult thymus after irradiation is markedly different from the Lyt phenotype of cells that initially populate the fetal thymus. The differences between adult and fetal thymic development that are observed in radiation bone marrow chimeras may be important in our understanding of T cell differentiation in these animals.

Differences in the MHC-restricted self-recognition repertoire of intra-thymic and extra-thymic cytotoxic T lymphocyte precursors

The MHC specificity of TNP-specific pCTL from the thymus and spleen of F1 leads to parent chimeras was evaluated. It was found that in the presence of exogenously added helper factor IL 2, thymic pCTL were restricted to recognizing TNP only in association with host MHC determinants, whereas splenic pCTL recognized TNP in association with either host or donor MHC determinants. Thus, the spleens of F1 leads to parent chimeras contain a pCTL repertoire that is not present intrathymically. Data are presented which suggest that such pCTL did nevertheless differentiate into functional competence in the chimeric host. These results are consistent with extra-thymic differentiation as the mechanism by which such nonthymically restricted pCTL may have developed.

Analysis of Fc (IgG) receptors on human peripheral blood leukocytes by dual fluorescence flow microfluorometry. II. Quantitation of receptors on cells that express the OKM1, OKT3, OKT4, and OKT8 antigens

Human peripheral blood mononuclear cells were analyzed for the expression of Fc(IgG) receptors (FcR) by a quantitative dual fluorescence flow microfluorometric (FMF) technique. Mononuclear cells from all donors tested were distributed into three distinct subsets on the basis of FcR expression: cells expressing high, intermediate, or background levels of FcR. To characterize these subsets, cells were doubly labeled for FcR and with OKM1, OKT3, OKT4, or OKT8 hybridoma antibodies by using nonoverlapping red and green fluorophores. Each cell was then analyzed for the presence of both labels with a dual laser flow cytometer. Cells that did not express FcR were heterogeneous for OKT3, OKT4, and OKT8, did not express OKM1, and were primarily T cells on the basis of rosette formation with sheep erythrocytes (E+ cells). Most of the cells that expressed intermediate levels of FcR (an average of 1.3 x 10(4) FcR/cell) also expressed high levels of OKM1 but did not bind OKT3, OKT4, or OKT8 hybridoma antibodies. These cells were characterized as monocytes because they were removed by passage over Sephadex G-10 columns and because they were larger than the other cells as judged by light scatter. The majority of cells with the highest FcR density (an average of 4.5 x 10(4) FcR/cell) formed rosettes with E and were, by definition, T gamma cells. These cells expressed negligible levels of OKT4 and intermediate levels of OKM1, levels that clearly distinquished them from monocytes. The T gamma cells were heterogeneous in the expression of both OKT3 and OKT8, with approximately 20% being positive for OKT3 and OKT8. The level of OKT3 expression for the OKT3 and OKT8. The level of OKT3 expression for the OKT3+ T gamma cells was about the same as for as for OKT3+ T nongamma cells. In contrast, the OKT8 T nongamma cells expressed lower levels of OKT8 than did the OKT8+ T nongamma cells. By compaing our results with those obtained by other invesigators, we tentatively assigned functions to the subsets of cells that we describe here.

Differences in the MHC-restricted self-recognition repertoire of intra-thymic and extra-thymic cytotoxic T lymphocyte precursors

The MHC specificity of TNP-specific pCTL from the thymus and spleen of F1 leads to parent chimeras was evaluated. It was found that in the presence of exogenously added helper factor IL 2, thymic pCTL were restricted to recognizing TNP only in association with host MHC determinants, whereas splenic pCTL recognized TNP in association with either host or donor MHC determinants. Thus, the spleens of F1 leads to parent chimeras contain a pCTL repertoire that is not present intrathymically. Data are presented which suggest that such pCTL did nevertheless differentiate into functional competence in the chimeric host. These results are consistent with extra-thymic differentiation as the mechanism by which such nonthymically restricted pCTL may have developed.

Analysis of Fc (IgG) receptors on human peripheral blood leukocytes by dual fluorescence flow microfluorometry. II. Quantitation of receptors on cells that express the OKM1, OKT3, OKT4, and OKT8 antigens

Human peripheral blood mononuclear cells were analyzed for the expression of Fc(IgG) receptors (FcR) by a quantitative dual fluorescence flow microfluorometric (FMF) technique. Mononuclear cells from all donors tested were distributed into three distinct subsets on the basis of FcR expression: cells expressing high, intermediate, or background levels of FcR. To characterize these subsets, cells were doubly labeled for FcR and with OKM1, OKT3, OKT4, or OKT8 hybridoma antibodies by using nonoverlapping red and green fluorophores. Each cell was then analyzed for the presence of both labels with a dual laser flow cytometer. Cells that did not express FcR were heterogeneous for OKT3, OKT4, and OKT8, did not express OKM1, and were primarily T cells on the basis of rosette formation with sheep erythrocytes (E+ cells). Most of the cells that expressed intermediate levels of FcR (an average of 1.3 x 10(4) FcR/cell) also expressed high levels of OKM1 but did not bind OKT3, OKT4, or OKT8 hybridoma antibodies. These cells were characterized as monocytes because they were removed by passage over Sephadex G-10 columns and because they were larger than the other cells as judged by light scatter. The majority of cells with the highest FcR density (an average of 4.5 x 10(4) FcR/cell) formed rosettes with E and were, by definition, T gamma cells. These cells expressed negligible levels of OKT4 and intermediate levels of OKM1, levels that clearly distinquished them from monocytes. The T gamma cells were heterogeneous in the expression of both OKT3 and OKT8, with approximately 20% being positive for OKT3 and OKT8. The level of OKT3 expression for the OKT3 and OKT8. The level of OKT3 expression for the OKT3+ T gamma cells was about the same as for as for OKT3+ T nongamma cells. In contrast, the OKT8 T nongamma cells expressed lower levels of OKT8 than did the OKT8+ T nongamma cells. By compaing our results with those obtained by other invesigators, we tentatively assigned functions to the subsets of cells that we describe here.

Immunoglobulin gene rearrangement and cell surface antigen expression in acute lymphocytic leukemias of T cell and B cell precursor origins

We have explored the relationship among immunoglobulin gene rearrangement, cytoplasmic immunoglobulin production, and cell surface antigen expression within 37 cases of acute lymphocytic leukemia. All 12 cases of the T cell type had germ-line kappa and lambda genes and 11 of 12 had germ-line heavy chain genes. In contrast, all 25 cases of the "non-T, non-B" classification, which lacked both definitive T cell markers and surface immunoglobulin, had rearranged immunoglobulin genes, indicating that they represent precursor cells already committed to the B cell lineage at the gene level. 14 had rearranged heavy chain genes, yet retained germ-line light chain genes, whereas 11 cases had both heavy and light chain gene reorganizations. All patterns of immunoglobulin gene rearrangement predicted by a model that proceeds from heavy chain gene recombination to light chain genes were observed. Despite the uniform presence of rearranged immunoglobulin genes, only five cases produced cytoplasmic mu-chain, one exceptional case produced gamma-chain, and another produced only lambda-chain. The cases of B cell precursor type that do not produce immunoglobulin may represent cells that frequently possess ineffectively rearranged immunoglobulin genes. Included in this group may be a set of cells trapped within the B cell precursor series because their ineffective rearrangements have eliminated certain gene subsegments necessary for the assemblage of an effective heavy chain gene. All seven cases of the non-T, non-B subgroup that bore HLA-DR but lacked CALLA (the common acute lymphocytic leukemia-associated antigen) represented the earliest recognizable stage of B cell precursors with rearranged heavy chain genes but germ-line light chain genes. Correlations here suggest that cells entering B cell development express HLA-DR and rearrange heavy chain genes before the expression of a B cell-associated antigen recognized by the antibody BA-1, the antigen CALLA, and any subsequent light chain gene rearrangements.

The human autologous mixed lymphocyte reaction. II. Analysis of activation and proliferation

In this study, we have used cell cycle analysis as an independent measure of proliferation and the 4F2 marker to enumerate activated T cells. T-cell proliferation increased gradually throughout the 7-day culture. The degree of proliferation correlated very strongly (r = 0 . 827, p less than 10(-4)) with the degree of T-cell activation as demonstrated by the expression of the 4F2 marker. However, many more T cells became activated during the AMLR than were proliferating. Thymidine incorporation correlated well (r = 0.956, p less than 10(-4)) with numbers of proliferating cells as determined by cell cycle analysis. Adherent cells (M phi) induced fewer T cells to express 4F2 and to proliferate than did (B + null) cells. However, proportionately, M phi induced much more activation than proliferation in comparison to (B + null) cells. Additional analyses of cell cycle and the 4F2 marker for activated cells indicated that a very small percentage of responder T cells (less than 1%) respond initially to signals from autologous non-T cells. Moreover, there is a three-day delay before substantial proliferation and activation takes place, providing time for amplification and suppressive regulatory processes. Ultimately, between 5 and 30% of the initial T cells are capable of proliferating in the AMLR and up to 90% of the cells may become activated. Thus, many cells become activated (and are therefore capable of secreting immune regulatory factors or otherwise participating in immune responses) than proliferate. These results provide a basis for analysing defects in the AMLR in association with various disease states.

Normal human B cells display ordered light chain gene rearrangements and deletions

Human kappa-producing B cell lines and leukemias retain their excluded lambda light chain genes in the germ line configuration, whereas transformed lambda-producing B cells uniformly rearrange or delete their kappa genes (12). Whether the unexpected lambda gene recombinations within malignant lambda-producing B cells reflect a normal developmental process or are secondary to transformation and specific chromosomal translocations was uncertain. To resolve this issue, we purified circulating lambda-bearing B cells from a normal individual to 97% purity by using a series of negative selection steps and a final positive selection on a cell sorter. Over 95% of the collective kappa genes in these lambda B cells were no longer in their germ line form, with the majority (60%) deleted and the remainder present but in a rearranged state. The chromosomal loss of the germ line kappa genes included the joining (J kappa) segments as well as the constant (C kappa) region, yet the particular variable (V kappa) gene family studied was spared. In addition, the incidence of kappa gene deletions was higher in long-term than in freshly transformed lambda B cell lines. This implies that the deletion of aberrantly rearranged kappa genes may occur as a second event. Such a mechanism would serve to eliminate aberrant transcripts and light chain fragments that might interfere with the synthesis and assembly of effective immunoglobulin molecules. Thus, despite the nearly equal usage of kappa and lambda light chain genes in man, there appears to be a sequential order to their expression during normal B cell ontogeny in which kappa gene rearrangements precede those of lambda.

Idiotypes of anti-Ia antibodies. II. Effects of in vivo treatment with xenogeneic anti-idiotype

The effects of in vivo treatment with xenogeneic anti-idiotypic antibodies were examined in an anti-Ia idiotypic system. Monoclonal antibody 14-4-4S, specific for Ia.7, has been shown to bear idiotopes that are expressed at readily detectable levels in conventional alloantibody responses. Sera from mice treated with purified anti-idiotypic antibodies (anti-Id) were found to contain inhibitory activity in an ELISA specific for the 14-4-4S Id, whereas sera from control mice treated with heterologous normal Ig did not. In addition, sera of anti-Id-treated C3H.SW mice contained specific anti-I-E activity, shown by binding to B10.A(2R) but not B10.A(4R) LPS blasts in flow microfluorometry. The anti-I-E induced by anti-Id included more IgG1 than IgG2. Even though a significant amount of anti-I-E activity was present in the serum, absorption analysis showed that most of the idiotope-positive antibody was not I-Ek-specific. Penetrance of induction of anti-I-E by anti-Id was 100% in the C3H.SW mice tested, and activity persisted in the serum for at least 8 to 9 mo in some cases. B10 mice produced only marginal anti-I-E activity after treatment, suggesting that induction is due to specific triggering rather than due entirely to a resemblance of anti-Id to the I-E antigen. The results thus indicate long-lasting alterations in an anti-Ia idiotypic system in the absence of exposure to conventional antigen, and represent specific manipulation of anti-Ia immunity.

Idiotypes of anti-Ia antibodies. II. Effects of in vivo treatment with xenogeneic anti-idiotype

The effects of in vivo treatment with xenogeneic anti-idiotypic antibodies were examined in an anti-Ia idiotypic system. Monoclonal antibody 14-4-4S, specific for Ia.7, has been shown to bear idiotopes that are expressed at readily detectable levels in conventional alloantibody responses. Sera from mice treated with purified anti-idiotypic antibodies (anti-Id) were found to contain inhibitory activity in an ELISA specific for the 14-4-4S Id, whereas sera from control mice treated with heterologous normal Ig did not. In addition, sera of anti-Id-treated C3H.SW mice contained specific anti-I-E activity, shown by binding to B10.A(2R) but not B10.A(4R) LPS blasts in flow microfluorometry. The anti-I-E induced by anti-Id included more IgG1 than IgG2. Even though a significant amount of anti-I-E activity was present in the serum, absorption analysis showed that most of the idiotope-positive antibody was not I-Ek-specific. Penetrance of induction of anti-I-E by anti-Id was 100% in the C3H.SW mice tested, and activity persisted in the serum for at least 8 to 9 mo in some cases. B10 mice produced only marginal anti-I-E activity after treatment, suggesting that induction is due to specific triggering rather than due entirely to a resemblance of anti-Id to the I-E antigen. The results thus indicate long-lasting alterations in an anti-Ia idiotypic system in the absence of exposure to conventional antigen, and represent specific manipulation of anti-Ia immunity.

Detection of a common antigen on murine B cells and Lyt-2+ T cells by a rat monoclonal antibody, 14D10

This paper reports the production of a rat monoclonal antibody, 14D10, which recognizes a determinant shared between B cells and Lyt-2+ T cells. Three subpopulations of spleen cells were defined based on the density of bound 14D10. They have been designated 14D10-SP (strongly positive), 14D10-WP (weakly positive), and 14D10-N (negative). Dual parameter immunofluorescence studies showed that 90% of 14D10-SP cells are IgM+ cells and more than 92% IgM+ cells are 14D10-SP. Of 14D10-WP cells, approximately 60% are Lyt-1+2+ T cells and less than 10% are IgM+ cells. However, most (greater than 90%) of Lyt-2+ T cells are reactive with 14D10. Staining of purified populations of Lyt-2+ and Lyt-2- T cells with fluoresceinated 14D10 also showed greater than 90% of Lyt-2+ T cells to be 14D10+, and fewer than 10% of Lyt-2- T cells are 14D10+. Mouse thymus contained very few (congruent to 5%) 14D10+ cells. Analysis of bone marrow cells shows almost all small cells to be 14D10+. Six Abelson virus-transformed cell lines all express the antigen recognized by 14D10.

Detection of a common antigen on murine B cells and Lyt-2+ T cells by a rat monoclonal antibody, 14D10

This paper reports the production of a rat monoclonal antibody, 14D10, which recognizes a determinant shared between B cells and Lyt-2+ T cells. Three subpopulations of spleen cells were defined based on the density of bound 14D10. They have been designated 14D10-SP (strongly positive), 14D10-WP (weakly positive), and 14D10-N (negative). Dual parameter immunofluorescence studies showed that 90% of 14D10-SP cells are IgM+ cells and more than 92% IgM+ cells are 14D10-SP. Of 14D10-WP cells, approximately 60% are Lyt-1+2+ T cells and less than 10% are IgM+ cells. However, most (greater than 90%) of Lyt-2+ T cells are reactive with 14D10. Staining of purified populations of Lyt-2+ and Lyt-2- T cells with fluoresceinated 14D10 also showed greater than 90% of Lyt-2+ T cells to be 14D10+, and fewer than 10% of Lyt-2- T cells are 14D10+. Mouse thymus contained very few (congruent to 5%) 14D10+ cells. Analysis of bone marrow cells shows almost all small cells to be 14D10+. Six Abelson virus-transformed cell lines all express the antigen recognized by 14D10.

Tolerance of thymocytes to allogeneic I region determinants encountered prethymically. Evidence for expression of anti-Ia receptors by T cell precursors before their entry into the thymus

The present study has assessed whether precursor T cells express receptors specific for the recognition of allogeneic I region-encoded determinants before their entry into the thymus. Because the ability of thymocytes to proliferate in response to allogeneic stimulator cells was shown to primarily result from the recognition of allogeneic I region determinants, thymocytes must already express anti-Ia receptors. In contrast, the expression of anti- Ia receptors by functionally immature thymocyte precursors could not be directly assessed by mixed lymphocyte reaction reactivity. However, expression of anti-Ia receptors by thymocyte precursors could be assessed by their ability to be specifically tolerized by the allogeneic Ia determinants that they encountered during their differentiation. To determine whether T cell precursors could specifically recognize and be tolerized to allogeneic Ia determinants expressed prethymically, thymus- engrafted radiation bone marrow chimeras were constructed [A {arrow} A x B (Tx + A Thy)] such that strain A T cells would be differentiating within a syngeneic strain A thymus but would have been previously exposed to the allogeneic strain B Ia determinants of the irradiated A x B host. The strain A thymocytes from these experimental animals were indeed tolerant to the extrathymic allogeneic strain B Ia determinants expressed by the irradiated host. Such tolerance was not mediated by detectable suppression and was not explained by the presence intrathymically of extrathymic allogeneic Ia determinants. Thus, these results suggest that T cell precursors can be specifically tolerized entry into the thymus. In addition, the failure to detect the generation of thymocytes with specificity for the allogeneic Ia determinants of the irradiated host, which were not deleted prethymically, argues that novel anti-allo Ia receptor specificities are not generated intrathymically.

B lymphocyte subpopulation defined by a rat monoclonal antibody, 14G8

14G8 is monoclonal rat antibody that recognizes an antigen found on 30 to 40% of B lymphocytes from normal mice and on approximately 65% of B lymphocytes from mice with the xid-determined immune defect. 14G8+ B cells from normal mice resemble B cells from mice with the xid-determined defect in that the median amount of membrane IgM expressed per cell is much larger than that of 14G8- B cells. The frequency of 14G8+ cells is highest in neonatal mice (approximately 55% of all spleen cells) and falls with age to approximately 25% of all spleen cells in adult mice. Relatively few lymph node or bone marrow B cells express the antigen recognized by 14G8. 14G8 also reacts with 50% of resident peritoneal cells and with red blood cells. 14G8+ and 14G8- B cell preparations were obtained by fluorescence-activated cell sorting and by adherence to 14G8 coated dishes. 14G8+ cells responded with in vitro proliferation to both anti-mu and to LPS. Cell cycle analysis indicated that approximately 33% of these cells entered S phase in response to LPS and 38% in response to anti-mu. In contrast, 14G8- cells responded poorly to LPS (7% of cells entered S phase) although they showed good responses to anti-mu (40% of cells entered S phase). Thus, 14G8+ B cells, despite their similarity to B cells from mice with the xid defect, can proliferate to anti-mu, which B cells from defective mice fail to do. 14G8 provides a monoclonal antibody valuable in the description of functional B cell subpopulations.

B lymphocyte subpopulation defined by a rat monoclonal antibody, 14G8

14G8 is monoclonal rat antibody that recognizes an antigen found on 30 to 40% of B lymphocytes from normal mice and on approximately 65% of B lymphocytes from mice with the xid-determined immune defect. 14G8+ B cells from normal mice resemble B cells from mice with the xid-determined defect in that the median amount of membrane IgM expressed per cell is much larger than that of 14G8- B cells. The frequency of 14G8+ cells is highest in neonatal mice (approximately 55% of all spleen cells) and falls with age to approximately 25% of all spleen cells in adult mice. Relatively few lymph node or bone marrow B cells express the antigen recognized by 14G8. 14G8 also reacts with 50% of resident peritoneal cells and with red blood cells. 14G8+ and 14G8- B cell preparations were obtained by fluorescence-activated cell sorting and by adherence to 14G8 coated dishes. 14G8+ cells responded with in vitro proliferation to both anti-mu and to LPS. Cell cycle analysis indicated that approximately 33% of these cells entered S phase in response to LPS and 38% in response to anti-mu. In contrast, 14G8- cells responded poorly to LPS (7% of cells entered S phase) although they showed good responses to anti-mu (40% of cells entered S phase). Thus, 14G8+ B cells, despite their similarity to B cells from mice with the xid defect, can proliferate to anti-mu, which B cells from defective mice fail to do. 14G8 provides a monoclonal antibody valuable in the description of functional B cell subpopulations.

Expression on normal lymphocytes of two cell surface antigens, XenCSA and GIX, related to the major glycoproteins (gp70) of murine leukemia viruses

XenCSA and GIX are two cell surface antigens related to the major envelope glycoproteins (gp70) of murine leukemia viruses. The levels of expression of these gp70 determinants were assessed in 36 recombinant inbred mouse strains and selected backcrosses derived from crosses between C57BL/6 with DBA/2 and C3H/He. These two antigens segregated in backcross mice and showed a different strain distribution pattern among the recombinant inbred mice, demonstrating that XenCSA and GIX are distinct genetic markers for different endogenous gp70 sequences. It was also shown that independent sets of gene regulate the expression of XenCSA and GIX.

Expression on normal lymphocytes of two cell surface antigens, XenCSA and GIX, related to the major glycoproteins (gp70) of murine leukemia viruses

XenCSA and GIX are two cell surface antigens related to the major envelope glycoproteins (gp70) of murine leukemia viruses. The levels of expression of these gp70 determinants were assessed in 36 recombinant inbred mouse strains and selected backcrosses derived from crosses between C57BL/6 with DBA/2 and C3H/He. These two antigens segregated in backcross mice and showed a different strain distribution pattern among the recombinant inbred mice, demonstrating that XenCSA and GIX are distinct genetic markers for different endogenous gp70 sequences. It was also shown that independent sets of gene regulate the expression of XenCSA and GIX.

Texas Red, a hydrophilic, red-emitting fluorophore for use with fluorescein in dual parameter flow microfluorometric and fluorescence microscopic studies

The sulfonylchloride derivative of the red-emitting fluorophore, sulforhodamine 101, has been synthesized in order to provide a reagent for coupling to amino groups on proteins and other compounds, and it is now commercially available under the name 'Texas Red'. Texas Red conjugates of antibodies and other proteins have been prepared in high protein yields; these conjugates retained their biological activities and were strongly fluorescent. The excitation and emission spectra of Texas Red conjugates are widely separated from those of molecules labeled with fluorescein isothiocyanate. Texas Red is therefore an excellent reagent for use in single or dual label flow microfluorometric and fluorescent microscopic studies.