The CD4 T cell-deficient mouse mutation nackt (nkt) involves a deletion in the cathepsin L (CtsI) gene

We recently reported a novel autosomal recessive mouse mutation designated nackt (nkt). Homozygous mutant mice have diffuse alopecia and a marked reduction in the proportion of CD4+ T cells in the thymus and peripheral lymphoid tissues. Here we show that the CD4 T-cell deficiency is due to a defect in the thymic microenvironment rather than the hematopoietic compartment. Furthermore, we identified the molecular basis of the mutant phenotype by demonstrating that the nkt mutation represents a 118-bp deletion of the cathepsin L (Ctsl) gene which is required for degradation of the invariant chain, a critical chaperone for major histocompatibility complex class II molecules. This finding explains the similarities in skin and immune defects observed in nkt/nkt and Ctsl -/- mice. The data reported here provide further in vivo evidence that the lysosomal cysteine protease cathepsin L plays a critical role in CD4+ T-cell selection in the thymus.

Effects of calorie restriction on thymocyte growth, death and maturation

We previously reported that calorie restriction (CR) significantly delays the spontaneous development of thymic lymphomas and other neoplasms in p53-deficient mice and their wild-type littermates. The purpose of the present study was to further characterize the anti-lymphoma effects of CR by assessing thymocyte growth, death and maturation in response to acute (6 day) and chronic (28 day) CR regimens. Male C57BL/6J mice fed a CR diet (restricted to 60% of control ad libitum intake) for 6 days displayed a severe reduction in thymic size and cellularity, as well as a decrease in splenic size and cellularity; these declines were sustained through 28 days of CR. Mice maintained on a CR diet for 28 days also displayed a significant depletion in the cell numbers of all four major thymocyte subsets defined by CD4 and CD8 expression. Analysis within the immature CD4(-)8(-) thymocyte subset further revealed an alteration in normal CD44 and CD25 subset distribution. In particular, CR for 28 days resulted in a significant decrease in the percentage of the proliferative CD44(-)25(-) subset. In addition, a significant increase in the percentage of the early, pro-T cell CD44(+)25(-) population was detected, indicative of a CR-induced delay in thymocyte maturation. Taken together, these findings suggest that CR suppresses (through several putative mechanisms) lymphomagenesis by reducing the pool of immature thymocytes that constitute the lymphoma-susceptible subpopulation.

Cyclin D2 overexpression in transgenic mice induces thymic and epidermal hyperplasia whereas cyclin D3 expression results only in epidermal hyperplasia

In a previous report, we described the effects of cyclin D1 expression in epithelial tissues of transgenic mice. To study the involvement of D-type cyclins (D1, D2, and D3) in epithelial growth and differentiation and their putative role as oncogenes in skin, transgenic mice were developed which carry cyclin D2 or D3 genes driven by a keratin 5 promoter. As expected, both transgenic lines showed expression of these proteins in most of the squamous tissues analyzed. Epidermal proliferation increased in transgenic animals and basal cell hyperplasia was observed. All of the animals also had a minor thickening of the epidermis. The pattern of expression of keratin 1 and keratin 5 indicated that epidermal differentiation was not affected. Transgenic K5D2 mice developed mild thymic hyperplasia that reversed at 4 months of age. On the other hand, high expression of cyclin D3 in the thymus did not produce hyperplasia. This model provides in vivo evidence of the action of cyclin D2 and cyclin D3 as mediators of proliferation in squamous epithelial cells. A direct comparison among the three D-type cyclin transgenic mice suggests that cyclin D1 and cyclin D2 have similar roles in epithelial thymus cells. However, overexpression of each D-type cyclin produces a distinct phenotype in thymic epithelial cells.

TCR v(beta) repertoire restriction and lack of CDR3 conservation implicate TCR-superantigen interactions in promoting the clonal evolution of murine thymic lymphomas

Thymic lymphoma development is a multistage process in which genetic and epigenetic events cooperate in the emergence of a malignant clone. The notion that signaling via TCR-ligand interactions plays a role in promoting the expansion of developing neoplastic clones is a matter of debate. To investigate this issue, we determined the TCR V(beta) repertoire of thymic lymphomas induced in AKR/J mice by either endogenous retroviruses or the carcinogen, N-methyl-N-nitrosourea (MNU). Both spontaneous and MNU-induced lymphomas displayed restricted V(beta) repertoires. However, whereas V(beta)6, V(beta)8 and V(beta)9 were expressed by a greater than expected frequency of MNU-induced lymphomas, V(beta)8, V(beta)7, V(beta)13 and V(beta)14 were over-represented on spontaneous lymphomas. The dissimilar TCR V(beta) profiles indicate that different endogenous ligands promote neoplastic clonal expansion in untreated and MNU-treated mice. Although the nature of these ligands is not clear, the lack of conservation in TCR beta chain CDR3 regions among lymphomas that express the same V(beta) segment suggests that endogenous superantigens (SAG), as opposed to conventional peptide ligands, are likely to be involved in the selection process. The biased representation of lymphomas expressing V(beta)6-, V(beta)7- and V(beta)9-containing TCRs that recognize endogenous SAG is consistent with this hypothesis. The finding that Bcl-2 is expressed at high levels in spontaneous and MNU-induced lymphomas suggests that preneoplastic thymocytes may be resistant to SAG-induced clonal deletion. A working model is presented in which preneoplastic clones expressing TCRs that recognize endogenous SAG are selectively expanded as a consequence of sustained TCR-mediated signaling.

Transgenic expression of cyclin D1 in thymic epithelial precursors promotes epithelial and T cell development

We previously reported that precursors within the keratin (K) 8+5+ thymic epithelial cell (TEC) subset generate the major cortical K8+5- TEC population in a process dependent on T lineage commitment. This report demonstrates that expression of a cyclin D1 transgene in K8+5+ TECs expands this subset and promotes TEC and thymocyte development. Cyclin D1 transgene expression is not sufficient to induce TEC differentiation in the absence of T lineage-committed thymocytes because TECs from both hCD3epsilon transgenic and hCD3epsilon/cyclin D1 double transgenic mice remain blocked at the K8+5+ maturation stage. However, enforced cyclin D1 expression does expand the developmental window during which K8+5+ cells can differentiate in response to normal hemopoietic precursors. Thus, enhancement of thymic function may be achieved by manipulating the growth and/or survival of TEC precursors within the K8+5+ subset.

Interdependence of cortical thymic epithelial cell differentiation and T-lineage commitment

Thymocyte and thymic epithelial cell (TEC) development are interdependent processes. Although lineage relationships among progressively maturing thymocyte subsets have been characterized, the developmental relationships among TEC subsets are obscure. Because epithelial cells express distinct keratin (K) species as a function of differentiation stage and proliferative status, we used K expression patterns to identify mouse TEC subsets and determine their lineage relationships. As expected, cortical and medullary TEC subsets express distinct K expression patterns in the normal thymus. However, we detected two distinct cortical TEC subsets, a major K8(+)K5(-) subset and a minor K8(+)K5(+) subset, which is highly represented at the cortico-medullary junction. Both cortical TEC subsets are also present in recombination activating gene 1 (RAG-1(-/-)) and TCRbetaxdelta-/- thymi in which T-cell development is blocked at the CD4(-)CD8(-)CD25(+)CD44(-) pre-T cell stage. In contrast, K8(+)K5(+) TECs predominate in the thymi of human CD3epsilon transgenic mice in which thymocyte development is blocked at an earlier CD4(-)CD8(-)CD25(-)CD44(+) stage. Transplantation of newborn human CD3epsilon transgenic thymi under the kidney capsule of RAG-1(-/-) mice results in the emergence of K8(+)K5(-) TECs concomitant with the appearance of CD25(+) thymocytes. Together, the data suggest that cortical TEC development proceeds from a K8(+)K5(+) precursor subset to a K8(+)K5(-) stage in a differentiation process concomitant with T-cell lineage commitment.

Cross-linking the TCR complex induces apoptosis in CD4+8+ thymocytes in the presence of cyclosporin A

Although it is generally agreed that TCR ligation is a minimal requirement for negative selection in the CD4+8+ double-positive (DP) thymocyte subset, the costimulatory requirements and specific signaling events necessary to induce apoptosis are not well defined. We have explored the consequences of cross-linking CD3/TCR complexes on thymocytes from H-Y TCR transgenic (Tg) mice. In agreement with previous reports, we demonstrate that culturing DP thymocytes with plate-bound anti-TCR antibody induces downregulation of CD4 and CD8 and upregulation of CD69 expression. Nevertheless, the activated cells did not undergo apoptosis, as determined by viable cell recoveries and by quantitation of DNA fragmentation using the TUNEL assay. However, specific depletion of the DP subset occurred within 24 hr when thymocytes were incubated in the presence of both anti-TCR and the immunosuppressant cyclosporin A (CsA). CsA also induced depletion of anti-CD3 stimulated normal DP thymocytes. Using mice homozygous for the lpr or gld mutation, we also have shown that Fas/Fas ligand interactions are not involved in the CsA-induced death of TCR-stimulated DP thymocytes. These data verify that TCR cross-linking alone is insufficient to induce apoptosis of DP thymocytes and further suggest that TCR stimulation activates a CsA-sensitive protective pathway that interferes with signaling events leading to apoptosis in DP thymocytes.

Localization of a novel chromosome 7 locus that suppresses development of N-Methyl-N-nitrosourea-induced murine thymic lymphomas

N-Methyl-N-nitrosourea (MNU) is a potent carcinogen that causes the development of murine thymic lymphomas. MNU-induced tumor incidence varies considerably among different inbred mouse strains. In particular, the AKR strain is highly susceptible, whereas the C57L strain is highly resistant to MNU-induced lymphoma formation. Crosses between AKR and C57L mice were established to investigate the genetic basis for the differential susceptibility of these inbred strains. A strong association between MNU-induced lymphoma development and coat color was observed in (AKR x C57)F2 and AKR x (AKR x C57)F1 progeny such that albino mice developed a higher tumor incidence than nonalbino animals. These data suggest that a locus on chromosome 7 influences tumor development. Analysis of four additional polymorphic loci (D7Rp2, Fes, Hbb, and Int-2) on chromosome 7 in AKR x (AKR x C57)F1 backcross mice revealed a significant linkage between high tumor incidence and homozygous inheritance of AKR alleles at the albino (tyrosinase) and Hbb loci. Thus, inheritance of at least one C57L allele at the albino or Hbb loci was associated with protection against MNU-induced lymphoma development. There was no association between tumor incidence and genotype at the D7Rp2, Fes, or Int-2 loci. Taken together, the data suggest that whereas C57L mice contain a dominant tumor suppressor gene on chromosome 7, in the AKR strain both alleles at this locus are defective resulting in enhanced susceptibility to MNU-induced lymphomagenesis.

Influence of murine leukemia proviral integrations on development of N-methyl-N-nitrosourea-induced thymic lymphomas in AKR mice

The AKR mouse strain is characterized by a high incidence of spontaneous thymic lymphoma that appears in older animals (greater than 6 months of age) and is associated with novel provirus integrations of ecotropic and recombinant murine leukemia viruses (MuLVs). Treatment of 4- to 6-week-old AKR/J mice with the carcinogen N-methyl-N-nitrosourea (MNU) results in thymic lymphomas that arise as early as 3 to 4 months of age and contain novel somatically acquired MuLV provirus integrations. The AKR/J strain develops MNU-induced lymphoma with a higher incidence and shorter latency than has been observed for other inbred mouse strains. To determine whether provirus integrations of endogenous MuLV account for the enhanced susceptibility of the AKR strain, the incidence and latency of MNU-induced lymphoma development was compared in AKR/J and AKR.Fv-1b mice. The restrictive b allele of the Fv-1 locus restricts integration and replication of endogenous N-tropic MuLV; therefore, AKR-Fv-1b mice have a very low incidence of spontaneous lymphoma. In contrast, AKR.Fv-1b mice develop MNU-induced lymphomas with an incidence and latency similar to those of the AKR/J strain. Furthermore, thymic lymphomas from both strains express an immature CD4-8+ phenotype, indicating neoplastic transformation of the same thymocyte subset. Southern blot analysis confirmed that lymphoma DNA from AKR.Fv-1b mice did not contain somatically acquired provirus integrations. These results demonstrate that provirus integration does not contribute to the predisposition of AKR mice to develop a high incidence of early MNU-induced lymphomas. Nevertheless, MNU treatment stimulated high-level expression of infectious ecotropic MuLV in AKR.Fv-1b as well as in AKR/J mice, suggesting that viral gene products might enhance lymphoma progression.

N-methyl-N-nitrosourea alters thymocyte subset distribution and targets immature CD4-8+ cells for lymphoma development

The majority of N-methyl-N-nitrosourea (MNU)-induced lymphomas in AKR/J mice express a CD4-8+ phenotype. The CD4-8+ subset in normal thymus contains functionally mature medullary cells and immature cycling cells. This study demonstrates that MNU-induced lymphomas correspond to the immature CD4-8+ subset. In addition, specific changes in the distribution of thymocyte subsets defined by CD4 and CD8 expression were observed after MNU treatment. Cortical thinning and selective depletion of immature CD4-8+ and CD4+8+ subsets occur immediately after treatment. In contrast, immature CD4-8- progenitors and mature medullary CD4+8- and CD4-8+ subsets are relatively resistant to cytotoxicity. Normal thymic architecture and subset distribution are restored within 2 weeks after which selective expansion of the immature CD4-8+ subset occurs. The data suggest that MNU induces neoplastic conversion in progenitor cells corresponding to the CD4-8- or immature CD4-8+ stages of thymocyte maturation.

Murine T-lymphomas corresponding to the immature CD4-8+ thymocyte subset

N-methyl-N-nitrosourea induces murine CD4-8+ T-lymphomas that express high levels of J11d and low levels of CD5 antigens, a phenotype characteristic of immature CD4-8+ thymocytes. This assignment is supported by the fact that CD4-8+ lymphoma cell lines acquire CD4 expression after intrathymic (i.t.) transfer, a finding consistent with the established precursor potential of the normal immature CD4-8+ subset. CD4+8+ lymphomas recovered after i.t. transfer maintain a CD4+8+ phenotype in long-term culture. Northern blot analyses reveal that CD4 expression is regulated at the transcriptional level in immature CD4-8+ and CD4+8+ cell lines. CD4-8+ lymphomas express low levels of functional CD3/TCR complexes that mediate intracellular Ca2+ mobilization in response to CD3 or alpha/beta-TCR monoclonal antibody. These data suggest that the immature CD4-8+ subset contains cells capable of undergoing TCR-mediated signaling and selection events. In contrast to normal immature CD4-8+ cells, which comprise a heterogeneous and transient subset, the CD4-8+ lymphoma lines provide stable, monoclonal models of the immature CD4-8+ stage of thymocyte development.

Nuclear events after activation of CD4+8+ thymocytes

Functionally mature T cells respond to stimulation via the Ag receptor by secretion of IL-2 and/or other lymphokines and by proliferation. However, immature CD4+8+ thymocytes do not secrete IL-2 or proliferate in response to stimulation. We have analyzed murine thymocyte populations enriched for CD4+ and CD4+8+ cells as well as the functionally mature CD4+ lymphoma C6VL-B and the CD4+8+ lymphoma 1010 for their ability to express mRNA related to early products of T cell activation signals. When stimulated with the calcium ionophore (Ionomycin) plus PMA, all the cells, regardless of their phenotype, accumulated abundant levels of c-myc mRNA. However, in contrast to the CD4+ thymocytes and C6VL-B, which accumulated abundant levels of IL-2 transcripts, neither the normal CD4+8+ thymocytes nor 1010 expressed IL-2 mRNA before or after stimulation. We have also examined these cells for the presence of the murine equivalents of two nuclear DNA-binding factors, NFAT-1 and NFIL2-A, which have been shown to be involved in IL-2 gene expression in human T cells. Our results indicate: 1) NFIL-2A binding activity is constitutively expressed in both CD4+ and CD4+8+ thymocytes and lymphomas and 2) NFAT-1 binding activity is readily detected in CD4+ thymocytes and C6VL-B, but is detected in very minimal amounts in populations enriched for CD4+8+ thymocytes and in 1010 upon activation. These results suggest that the failure of CD4+8+ thymocytes to express IL-2 mRNA upon stimulation may be in part due to the lack of inducibility of NFAT-1 binding activity, and that functional maturation of this population might be associated with acquisition of the ability to induce NFAT-1 activity.

Nuclear events after activation of CD4+8+ thymocytes

Functionally mature T cells respond to stimulation via the Ag receptor by secretion of IL-2 and/or other lymphokines and by proliferation. However, immature CD4+8+ thymocytes do not secrete IL-2 or proliferate in response to stimulation. We have analyzed murine thymocyte populations enriched for CD4+ and CD4+8+ cells as well as the functionally mature CD4+ lymphoma C6VL-B and the CD4+8+ lymphoma 1010 for their ability to express mRNA related to early products of T cell activation signals. When stimulated with the calcium ionophore (Ionomycin) plus PMA, all the cells, regardless of their phenotype, accumulated abundant levels of c-myc mRNA. However, in contrast to the CD4+ thymocytes and C6VL-B, which accumulated abundant levels of IL-2 transcripts, neither the normal CD4+8+ thymocytes nor 1010 expressed IL-2 mRNA before or after stimulation. We have also examined these cells for the presence of the murine equivalents of two nuclear DNA-binding factors, NFAT-1 and NFIL2-A, which have been shown to be involved in IL-2 gene expression in human T cells. Our results indicate: 1) NFIL-2A binding activity is constitutively expressed in both CD4+ and CD4+8+ thymocytes and lymphomas and 2) NFAT-1 binding activity is readily detected in CD4+ thymocytes and C6VL-B, but is detected in very minimal amounts in populations enriched for CD4+8+ thymocytes and in 1010 upon activation. These results suggest that the failure of CD4+8+ thymocytes to express IL-2 mRNA upon stimulation may be in part due to the lack of inducibility of NFAT-1 binding activity, and that functional maturation of this population might be associated with acquisition of the ability to induce NFAT-1 activity.

Genetics of N-methyl-N-nitrosourea induction of thymic lymphomas in AKR/J mice: assignment of a susceptibility gene to mouse chromosome 7

Treatment of young AKR/J mice with N-methyl-N-nitrosourea (MNU) results in the induction of a high incidence of thymic lymphomas occurring between 4 and 6 months of age. The tumor incidence is higher and the latency period is shorter than that observed in other MNU-treated mouse strains. Analysis of tumor incidence in crosses of AKR/J with C57L/J mice indicates that several genes influence the incidence and latency of MNU-induced thymic lymphomas. One of these genes appears to be tightly linked to the albino locus of chromosome 7.

Characterization of env gene recombination in x-ray--induced thymomas of C57BL/6 mice

A role for specific recombination events at the env region of endogenous murine leukemia virus (MuLV) sequences in radiation carcinogenesis in C57BL mice has been suggested by a number of studies. We characterized env-related cell surface antigens from a primary, x-ray--induced, and several transplanted C57BL/6 thymomas of viral and radiation etiologies by immunoprecipitation and two-dimensional peptide mapping. DNA from lymphoma cells was also analyzed by Southern blotting for evidence of mink cell focus-forming (MCF) type env recombination events. Although gp70 molecules with novel structural determinants were found on all transplanted lymphomas examined, expression of novel env antigens was variable among these lymphomas, and there was a lack of correlation of characteristic MCF-type env recombination events in endogenous retrovirus DNA sequences with novel env antigens on lymphoma cell surfaces. Neither novel gp70 antigens nor MCF-type env provirus recombinant structures were consistent features of the C57BL/6 thymomas of radiation etiology examined in this study, even though MCF-type env recombination events have been suggested as etiologically significant in MuLV-mediated lymphomagenesis in both RadLV and x-ray--induced tumors in C57BL/6 mice.

Altered expression of lymphocyte differentiation antigens on phorbol ester-activated CD4+8+ T cells

Altered expression of cell surface Ag is an early event accompanying Ag-, mitogen-, or phorbol ester-induced activation of mature T cells. In this report, phorbol ester-induced changes in the expression of several functionally significant cell surface molecules are explored on immature thymocytes and lymphoma cells presenting a cortical CD4+8+ double-positive (DP) phenotype. Both CD4 and CD8 expressions are down-modulated on DP cells incubated with PMA. Cell-surface expression of CD4 and CD8 remains depressed for 72 h in the presence of PMA, but is restored after removal of PMA from the culture medium. The PMA-mediated loss of Ag expression is associated with a rapid down-regulation of steady state CD4 and CD8 mRNA transcript levels in treated cells. The sustained loss of CD4 and CD8 surface expression on DP cells is a selective event because CD5 expression is enhanced, H-2 expression is unchanged, and CD3 expression is only transiently diminished by PMA stimulation. Other T cell-activating agents, including Con A, ionomycin, and anti-CD3 mAb, induce selected surface antigenic changes on DP cells, but do not mimic the pattern of altered Ag expression observed after PMA stimulation. These data demonstrate that, similar to mature subsets, T cells in the DP nonmature compartment undergo alterations in expression of functionally important cell-surface molecules in response to activating agents. Nevertheless, distinctions between mature and nonmature T cells regarding specific alterations in differentiation Ag phenotype suggest that the effect of PMA on expression of these molecules depends, in part, on the maturation stage of the target cell population.

Altered expression of lymphocyte differentiation antigens on phorbol ester-activated CD4+8+ T cells

Altered expression of cell surface Ag is an early event accompanying Ag-, mitogen-, or phorbol ester-induced activation of mature T cells. In this report, phorbol ester-induced changes in the expression of several functionally significant cell surface molecules are explored on immature thymocytes and lymphoma cells presenting a cortical CD4+8+ double-positive (DP) phenotype. Both CD4 and CD8 expressions are down-modulated on DP cells incubated with PMA. Cell-surface expression of CD4 and CD8 remains depressed for 72 h in the presence of PMA, but is restored after removal of PMA from the culture medium. The PMA-mediated loss of Ag expression is associated with a rapid down-regulation of steady state CD4 and CD8 mRNA transcript levels in treated cells. The sustained loss of CD4 and CD8 surface expression on DP cells is a selective event because CD5 expression is enhanced, H-2 expression is unchanged, and CD3 expression is only transiently diminished by PMA stimulation. Other T cell-activating agents, including Con A, ionomycin, and anti-CD3 mAb, induce selected surface antigenic changes on DP cells, but do not mimic the pattern of altered Ag expression observed after PMA stimulation. These data demonstrate that, similar to mature subsets, T cells in the DP nonmature compartment undergo alterations in expression of functionally important cell-surface molecules in response to activating agents. Nevertheless, distinctions between mature and nonmature T cells regarding specific alterations in differentiation Ag phenotype suggest that the effect of PMA on expression of these molecules depends, in part, on the maturation stage of the target cell population.

N-methyl-N-nitrosourea-induced T-lymphomas of AKR/J mice contain somatically acquired ecotropic-like murine leukemia proviruses

We have studied somatically murine leukemia proviral integrations in primary N-methyl-N-nitrosourea (MNU)-induced thymic lymphomas of AKR/J mice. The majority of MNU-induced lymphomas contain newly acquired murine leukemia proviral sequences. In contrast to spontaneous AKR/J lymphomas which contain multiple integrations of mink cell focus-forming recombinant proviruses, MNU-induced lymphomas contain ecotropic-related proviruses. This conclusion was based on the demonstration that EcoRI- and PvuII-digested DNA from MNU-induced lymphomas contains new 3' proviral-cellular junction fragments that hybridize with the ecotropic-specific pAKV-4 and pAKV-5 hybridization probes. Also, EcoRI/PstI double digests of DNA from MNU-induced lymphomas revealed that the acquired proviruses do not contain an internal 3' EcoRI site characteristic of mink cell focus-forming recombinant viruses. The proviral integration patterns suggest that MNU-induced lymphomas are clonal or oligoclonal in nature. This conclusion is supported by comparison of proviral integration patterns in lymphomas obtained from thymus and spleen of individual mice, and by analyses of T-cell receptor beta-chain gene rearrangements. The frequent occurrence of ecotropic-related proviral sequences in MNU-induced lymphomas suggests that these newly acquired proviruses may play a role in tumor development.

Alpha/beta T-cell antigen receptor gene and protein expression occurs at early stages of thymocyte differentiation

Alterations in gene expression that orchestrate eukaryotic cellular differentiation often require appropriate interactions between differentiating cells and a specialized microenvironment. During T-lymphocyte differentiation, immature thymocytes undergo a stringent intrathymic selection process that requires intimate contact with thymic stromal elements. Since this selection process generates T cells that are self-tolerant and recognize nominal antigen only within the context of self-major histocompatibility antigen complex molecules, it is possible that thymocyte/stromal cell interactions are mediated, in part, by antigen-specific receptors expressed on differentiating thymocytes. However, the developmental stage at which alpha/beta antigen-specific receptors are expressed during T-cell maturation has been a matter of debate. To address this issue, we have studied alpha/beta T-cell antigen receptor gene and protein expression on normal thymocyte subsets of AKR/J mice, as well as on a panel of AKR/J primary thymic lymphomas characterized for CD4 (L3T4) and CD8 (Lyt-2) differentiation antigen expression. The data unequivocally demonstrate that alpha/beta heterodimers are expressed not only on phenotypically mature thymocytes but also on the majority of CD4+8+ double-positive cells that comprise the predominant nonmature thymocyte subset. Furthermore, a fraction of thymocytes in the CD4-8- double-negative compartment, known to contain progenitor cells, also expresses readily detectable cell-surface alpha/beta receptors. Therefore, during the process of intrathymic selection, interactions between nonmature thymocytes and stromal cells via the antigen-receptor complex may play a pivotal role in T-cell differentiation and should be considered in formulating schemes for functional T-cell selection.

N-methyl-N-nitrosourea-induced and spontaneous AKR/J thymic lymphomas express distinct differentiation antigen phenotypes

Spontaneous and N-methyl-N-nitrosourea (MNU)-induced AKR/J thymic lymphomas were characterized for expression of several lymphocyte differentiation antigens. The majority (53%) of spontaneous lymphomas expressed both Lyt-2 and L3T4 antigens, similar to the predominant normal thymocyte subset. In contrast, 63% of the thymic lymphomas induced by the chemical carcinogen MNU, expressed an Lyt-2+ L3T4- antigenic profile. Although this profile suggested that MNU-induced lymphomas are phenotypically similar to a mature thymocyte subset, the presence of ThB antigen on Lyt-2+ L3T4- lymphomas did not support this notion. Diagonal gel electrophoresis of 125I-labeled membrane extracts and immunoprecipitates revealed that 17 of 29 Lyt-2+ L3T4-MNU-induced lymphomas expressed cell surface T-cell receptor heterodimer components. Northern blot analyses confirmed that the T-cell receptor material was composed of alpha and beta polypeptide chains. The results from this study indicate a distinct origin or differentiation potential of the target cells involved in viral and chemical induced lymphomagenesis of AKR/J mice.

Human milk-derived lactoferrin inhibits mitogen and alloantigen induced human lymphocyte proliferation

Purified lactoferrin (LF), isolated from human milk, was tested for its effect on human T-lymphocyte proliferative responses to phytohemagglutinin (PHA) and to alloantigens in mixed lymphocyte culture. LF inhibited proliferation in both assays in a dose-dependent manner. The suppressive effect was not due to LF mediated cytotoxicity since washing cells that had been pre-incubated with LF restored their proliferative activity. LF was most effective in suppressing the PHA response when added within 24 h of culture initiation. Iron saturated LF failed to inhibit PHA-induced proliferation, suggesting that the mechanisms of suppression involve the chelating property of LF. The suppressive effect of LF on T-lymphocyte proliferative response in vitro supports the notion that LF has significant immunoregulatory potential in vivo.

An analysis of the presence of Fc receptors on bone marrow lymphoblasts in acute lymphoblastic leukemia. A Pediatric Oncology Group study

The presence or absence of the Fc receptor (FcR) on bone marrow lymphoblasts was evaluated in 279 cases of acute lymphoblastic leukemia (ALL) by member institutions of the Pediatric Oncology Group (POG). The case material was classified as follows: 19 cases of positive (greater than or equal to 20% +), 24 additional cases as intermediate (greater than or equal to 10% but less than 20%), and the remaining 236 cases as negative (less than 10%). Intermediate and positive cases were relatively equally distributed between null cell leukemia and pre-B-cell leukemia, and there were one intermediate and two positive T-cell cases. One of two cases of B-cell leukemia was also positive. There were no distinguishing clinical or laboratory characteristics which distinguished the FcR+ cases, nor was the FcR of prognostic significance within ALL as a group or within immunologically defined phenotypes.

Proviral structure and differentiation antigen phenotype of spontaneous and chemically induced AKR lymphomas

AKR mice develop spontaneous thymomas after 6 months of age due to a novel class of murine leukemia viruses that are generated by a series of genetic recombinations between endogenous proviral loci. AKR mice also are more susceptible to N-methyl-N-nitrosourea (MNU)-induced thymomas than are low-leukemia-incidence mouse strains. To determine whether virally and chemically induced lymphomagenesis proceeds by similar pathways in AKR mice, spontaneous and MNU-induced thymic lymphomas were analyzed for a DNA restriction linkage generated during spontaneous tumor development by recombination between envelope genes of endogenous murine leukemia proviral loci. DNA from spontaneous thymic lymphomas invariably contained a restriction fragment characteristic of recombinant murine leukemia virus etiology, while four of five MNU-induced thymic lymphomas did not show this restriction linkage. In addition, analysis of lymphocyte differentiation antigen profiles indicated that MNU-induced lymphomas represent a more immature stage of T-cell differentiation than the majority of spontaneous lymphomas. These data suggest that there are fundamental differences in the mechanisms of induction of virally and chemically induced thymic lymphomas in AKR mice.

Distribution of T lymphocyte subsets in human colostrum

Lymphocytes were isolated from human colostrum and peripheral blood collected within 7 days postpartum. A 20-fold enrichment of lymphocytes from colostrum was achieved by centrifugal elutriation followed by equilibrium density gradient centrifugation. The distribution of T lymphocyte subsets was determined by immunofluorescence analysis of reactivity with monoclonal antibodies of the OKT series. In confirmation of previous reports employing sheep erythrocyte rosette assays, the majority of colostral lymphocytes reacted with OKT3 monoclonal antibody, a reagent that detects a surface antigen on mature T cells. Neither colostral nor blood lymphocytes from postpartum donors expressed the OKT6 antigen that is found in immature thymocytes. A novel finding is that the T lymphocyte population in colostrum contains both OKT4 (helper/inducer phenotype) and OKT8- (cytotoxic/suppressor phenotype) positive subsets. The relative ratio of OKT4 to OKT8-positive T cell subsets in colostrum, however, is generally lower than that observed for peripheral blood T cells.

Distribution of T lymphocyte subsets in human colostrum

Lymphocytes were isolated from human colostrum and peripheral blood collected within 7 days postpartum. A 20-fold enrichment of lymphocytes from colostrum was achieved by centrifugal elutriation followed by equilibrium density gradient centrifugation. The distribution of T lymphocyte subsets was determined by immunofluorescence analysis of reactivity with monoclonal antibodies of the OKT series. In confirmation of previous reports employing sheep erythrocyte rosette assays, the majority of colostral lymphocytes reacted with OKT3 monoclonal antibody, a reagent that detects a surface antigen on mature T cells. Neither colostral nor blood lymphocytes from postpartum donors expressed the OKT6 antigen that is found in immature thymocytes. A novel finding is that the T lymphocyte population in colostrum contains both OKT4 (helper/inducer phenotype) and OKT8- (cytotoxic/suppressor phenotype) positive subsets. The relative ratio of OKT4 to OKT8-positive T cell subsets in colostrum, however, is generally lower than that observed for peripheral blood T cells.

Heterogeneity of cell surface receptors and mitogen reactivity of individual spontaneous AKR lymphomas

Eight spontaneous thymic lymphomas from AKR mice were characterized individually in vitro for cell surface receptors and mitogen reactivity. One of the thymic lymphomas, designated 105, displayed receptors for the Fc region of immunoglobulin and for complement on a portion of the Thy-1-positive lymphoid blasts. The other T cell lymphomas did not display either receptor, and none expressed cell surface immunoglobulin. This was in contrast to the distinct behavior of each lymphoma in culture in both spontaneous and mitogen-stimulated tritiated thymidine [3H]-dThd uptake. After 48 h of culture, spontaneous [3H]-dThd uptake of the individual lymphomas ranged from 137 +/- 27 cpm to 100,442 +/- 13,422 cpm. Four of the spontaneous lymphomas did not respond to T cell mitogens by increased [3H]-dThd uptake. One lymphoma responded to the T cell mitogen concanavalin A only, whereas two lymphomas were stimulated by both phytohemagglutinin and concanavalin A. None of the lymphomas were stimulated by the B cell mitogen, lipopolysaccharide.

Separation of cytotoxic leukocyte populations of human peripheral blood and colostrum of PVP-silica (Percoll) density gradients

PVP-silica (Percoll) did not inhibit antibody-dependent cellular cytotoxicity in an 18 h 51Cr-release assay. By the use of a simple discontinuous density gradient centrifugation technique, leukocytes from peripheral blood and colostrum were separated into morphologic and cytotoxic functional populations. The major cytotoxic effector cells in colostrum are lipid-free macrophages and probably a small lymphocyte subpopulation.

T lymphocytes in colostrum and peripheral blood differ in their capacity to form thermostable E-rosettes

The cellular population of human breast milk collected within 5 days postpartum consists primarily of lipid laden polymorphonuclear leukocytes and macrophages, whereas lymphocytes comprise < 10% of the total cells. A discontinuous density gradient technique was developed to obtain highly enriched (75 +/- 6%) fractions of milk lymphocytes. The majority of milk lymphocytes are T cells as determined by their capacity to form rosettes at 4 degrees C with sheep erythrocytes (E). The lymphocytic origin of the rosetted cells was confirmed by morphologic evaluation of Wright-Giemsa-stained cytocentrifuge slides. A novel finding is that a large proportion of milk T lymphocytes form E-rosettes at 37 degrees C as well as at 4 degrees C. The capacity to form thermostable E-rosettes is not a general property of T lymphocytes in the postpartum period, since peripheral blood T lymphocytes from milk donors form few thermostable E-rosettes. In addition, peripheral blood lymphocytes did not acquire the capacity to form thermostable E-rosettes after density gradient centrifugation nor after incubation with autologous milk. The finding that T lymphocytes in milk form thermostable E-rosettes suggests that milk T lymphocytes may be activated or immature. In either case, these data support the concept that lymphocytes that home to the mammary gland are a select subset of the total lymphocyte population.

T lymphocytes in colostrum and peripheral blood differ in their capacity to form thermostable E-rosettes

The cellular population of human breast milk collected within 5 days postpartum consists primarily of lipid laden polymorphonuclear leukocytes and macrophages, whereas lymphocytes comprise < 10% of the total cells. A discontinuous density gradient technique was developed to obtain highly enriched (75 +/- 6%) fractions of milk lymphocytes. The majority of milk lymphocytes are T cells as determined by their capacity to form rosettes at 4 degrees C with sheep erythrocytes (E). The lymphocytic origin of the rosetted cells was confirmed by morphologic evaluation of Wright-Giemsa-stained cytocentrifuge slides. A novel finding is that a large proportion of milk T lymphocytes form E-rosettes at 37 degrees C as well as at 4 degrees C. The capacity to form thermostable E-rosettes is not a general property of T lymphocytes in the postpartum period, since peripheral blood T lymphocytes from milk donors form few thermostable E-rosettes. In addition, peripheral blood lymphocytes did not acquire the capacity to form thermostable E-rosettes after density gradient centrifugation nor after incubation with autologous milk. The finding that T lymphocytes in milk form thermostable E-rosettes suggests that milk T lymphocytes may be activated or immature. In either case, these data support the concept that lymphocytes that home to the mammary gland are a select subset of the total lymphocyte population.

A unique surface marker profile in T-cell acute lymphocytic leukemia

A 5-yr-old girl with acute lymphocytic leukemia presented with moderate hepatomegaly, marked splenomegaly, but no evidence of a mediastinal mass. The peripheral blood white count was 270 x 10(9)/liter with 99% leukemic cells. Surface marker analysis showed the lymphoblasts to be E-rosette negative and complement receptor positive. The patient's leukemic cells were unreactive with anti-p23,30, which detects Ia-like antigens, and strongly reactive with A99 anti-T-cell serum, which reacts with normal human thymocytes and peripheral blood T cells. The percentage of leukemic cells bearing complement receptors diminished during relapse. The leukemic cells obtained at diagnosis and during relapse were nonreactive to mitogens and alloantigens and failed to stimulate proliferation of normal lymphocytes in mixed lymphocyte culture. There was no evidence for active suppression of normal lymphocyte reactivity mediated by the leukemic cells. The surface marker and functional profile of these leukemic cells is consistent with that of an early stage in T-cell maturation.

The effects of a 10% soybean oil emulsion on lymphocyte transformation

Free essential fatty acids (EFA) are reported to suppress cell-mediated immunity. Because Intralipid contains a high concentration of esterified EFA, the effects of this emulsion on in vitro lymphocyte transformation were studied. Intralipid concentrations of 11.5, 115, and 230 mg% in lymphocyte cultures increased phytohemagglutinin (PHA) stimulation by an average of 8.2% (not significant [NS]), 18.1% (p < 0.01), and 11.8% (NS), respectively. These same concentrations also increased Varidase stimulation in lymphocyte cultures by an average of 11.3 (p < 0.02), 18.9 (p < 0.02), and 4.4% (NS), respectively. Control wells did not demonstrate allergic reactions to Intralipid. These data demonstrate that Intralipid can significantly increase the mitogenic response of human thymic lymphocytes and the antigenic response of human lymphocytes, in vitro.

Promotion of incidence of adenovirus type 12 transplantable tumors by carrageenan, a specific antimacrophage agent

Carrageenan, a sulfated polygalactose with known macrophage-toxic properties, was used to ascertain the role of macrophages in resistance to adenovirus type 12 transplantable tumors. A single ip injection of 5 or 10 mg carrageenan led to increased incidence and more rapid growth of tumors in C3H mice. Carrageenan was most effective if given 1 day before tumor inoculation; the effectiveness decreased with increasing intervals before or after tumor cell injection. The macrophage stabilizer poly-2-vinylpyridine N-oxide injected sc (150 mg/kg) 1 day before carrageenan was given reduced the incidence of tumors. These data lend further support to the importance of macrophages in tumor immunity.

Phytohemagglutinin response of murine spleen cells during pregnancy and inhibition of normal phytohemagglutinin response by pregnancy or post-partum serum

The in vitro blastogenic response of spleen cells to phytohemagglutinin-M (PHA) was evaluated as a measurement of the immunologic reactivity of virgin, pregnant and post-partum mice. In PHA-stimulated cultures 3H-thymidine incorporation by lymphocytes from post-partum mice was not significantly different from that of virgin age-matched control mice. Background 3H-thymidine incorporation was high in cultures from post-partum mice resulting in stimulation indices which were lower than those of virgin controls. Spleen cells from mice sacrificed after various intervals of pregnancy showed depressed PHA responsiveness only at the 15th day of gestation. The PHA response of normal spleen cells was depressed in the presence of serum from pregnant or post-partum mice.

Inhibition of the graft-versus-host reaction. III. Altered in vivo distribution of spleen cells pretreated with Fab fragments of antithymocyte globulin

51Cr-labeled parental strain spleen cells were pretreated in vitro with antithymocyte globulin (ATG) or Fab fragments of ATG before i.v. injection into F1 recipients. Recipients were killed at various intervals after injection and their organs were assayed for radioactivity in order to determine the in vivo distribution pattern of pretreated cells. 51Cr spleen cells pretreated with ATG were almost totally prevented from migrating to spleens, lymph nodes, bone marrow, Peyer's patches, lungs, and peripheral blood of recipients. Pretreatment of 51Cr spleen cells with noncytotoxic Fab of ATG also inhibited localization to these organs and tissues; however, the inhibition was not as complete as that of ATG-treated cells. Localization of Fab-treated 51Cr spleen cells to recipient nodes was inhibited to a greater extent than was localization to recipient spleens. There was no significant difference in the extent of inhibition of ATG-treated 51Cr spleen cells to recipient nodes and spleen. Organ counts from recipients killed at various intervals after injection of Fab-treated 51Cr spleen cells showed that Fab-treated cells do not recover their recirculating potential in vivo.

A New Serum Factor in Normal Rabbits

A hexapeptide was specifically cleaved from the C-terminus of the Fd of rabbit (Fab')2 fragments. The amino acid composition and sequence of the peptide was identical to that reported for the hinge peptide. These studies further showed that the hinge peptide could be recovered as a disulfide bonded dimer from d11 but not from d12 (Fab')2 fragments by digestion with CNBr.

The results of this investigation also demonstrated that the isolated peptides were reactive with a specific natural antiglobulin factor in rabbit sera, namely, homoreactant. As such, the peptide represents one of the smallest naturally occurring antigenic determinants isolated from a protein.

The chemical and serological properties of the isolated hinge peptide were confirmed by comparison with a synthetic peptide of determined amino acid sequence.