V(beta)8(+) T cells protect from demyelinating disease in a viral model of multiple sclerosis.

Previous studies illustrated the influence of T cell subsets on susceptibility or resistance to demyelination in the Theiler's murine encephalomyelitis virus (TMEV) model of multiple sclerosis. Genetic segregation analysis showed a correlation with disease phenotype in this model with particular V(beta) genes. In this study we investigated the contribution of specific V(beta) TCR to the pathogenesis of virus-induced demyelinating disease. Spectratype analysis of cells infiltrating the CNS early in infection demonstrated an over-representation of V(beta)8(+) T cells in mice expressing a susceptible H-2 haplotype. We infected transgenic mice expressing the V(beta)8.2 TCR directed against a non-TMEV antigen and found an increase in demyelinating disease in mice of either susceptible or resistant background compared with littermate controls. In addition, depletion studies with an anti-V(beta)8-specific antibody in both susceptible (B10.Q) and resistant (C57BL/6) mice resulted in increased demyelination. TCR analysis of VP2-specific cytotoxic T cell clones from mice with a resistant genotype identified only the V(beta)8.1 TCR, suggesting that limited T cell diversity is critical to TMEV clearance. Together, these results support a protective role for V(beta)8(+) T cells in virus-induced demyelinating disease.

Impact of V beta 8+/+ T cells on the development of increased airway reactivity and IgE production in SJL mice.

SJL mice have been extensively characterized as "low-responder" animals in terms of IgE-dependent immediate-type hypersensitivity responses. Since these mice are genetically deficient in certain TCR Vbeta gene segments, we asked whether this might be the reason for the "low-responder" status. Specifically in H-2d mice the TCR-Vbeta8.2 gene element has been shown to play an important role in Th2 immune responses to ovalbumin (OVA). Utilizing a TCR Vbeta8. 2-transgenic SJL (SJL Vbeta8+/+) mouse, we examined whether the H-2s -bearing "low-responder" mouse could be converted into a "high-responder" animal. Remarkably, non-sensitized SJL Vbeta8+/+ mice demonstrated strongly elevated levels of total IgE antibody. Mitogen-stimulated T cells from these mice released high amounts of IL-4 as compared to SJL wild-type (wt) mice. In addition, sensitization to OVA via the airways resulted in the development of increased airway responsiveness in SJL Vbeta8+/+ mice, but not in SJL wt animals. The results indicate that the capacity to produce IgE and IL-4 and to develop increased airway responsiveness can be restored in SJL wt mice by introducing the Vbeta8.2 gene segment into the TCR repertoire.

B cell-deficient mice have increased susceptibility to HSV-1 encephalomyelitis and mortality.

We studied the susceptibility of B cell-deficient mice to encephalomyelitis following intraperitoneal inoculation of HSV-1. B cell-deficient mice developed striking CNS signs including tail atony, clumsy gait and limb paralysis after HSV-1 infection. In addition, B cell-deficient mice had decreased survival (LD50 = 2.2 x 10(7) PFU) compared to control C57BL/6 mice (LD50 = 2.3 x 10(8) PFU). B cell-deficient mice had encephalomyelitis and detectable virus in the brain 7 days post-infection while C57BL/6 mice did not. Passive transfer of hyperimmune sera protected B cell-deficient mice from death, suggesting a role for antibody in susceptibility to HSV-1 encephalomyelitis.

In the absence of T cells, natural killer cells protect from mortality due to HSV-1 encephalitis.

The importance of natural killer (NK) cells in the resistance to herpes simplex virus type 1 (HSV-1), a common infection of immunocompromised patients, is unclear. Previous data on the role of NK cells in murine HSV-1 infection has been contradictory. Adoptive transfer studies suggested that NK cells mediated resistance to HSV-1, but in vivo depletion approaches demonstrated that NK cells were not important. We studied the course of HSV-1 infection after intranasal (i.n.) inoculation of E26 mice (lacking NK and T cells), T cell knockout (T cell ko) mice (lacking T cells only), or normal control mice. The E26 mice showed greater mortality and an impaired ability to clear virus from lung and brain compared to T cell ko mice and control mice, and had severe necrotizing HSV-1 encephalitis. Therefore, the data support the hypothesis that NK cells play an important role in the natural defense of murine HSV-1 infection.

Recombinant CD40L treatment protects allogeneic murine bone marrow transplant recipients from death caused by herpes simplex virus-1 infection.

Posttransplant infection associated with host immune deficiency is the major cause of nonrelapse mortality of human bone marrow transplant recipients. In a new murine model of posttransplant infection, allogeneic bone marrow transplant recipients were infected with herpes simplex virus-1 (HSV-1) via intraperitoneal inoculation 12 weeks after transplantation. Allogeneic transplant recipients with graft-versus-host disease (GVHD) had significantly increased mortality from HSV-1 encephalitis, with deficiencies of both specific anti-HSV-1 antibody and total serum IgG2a. GVHD mice displayed a Th2 cytokine profile (increased interleukin-4 [IL-4] and decreased interferon-gamma) and decreased lipopolysaccharide (LPS) responses, suggesting that both T-cell and B-cell defects contributed to the impaired production of antibody. Because passive transfer of hyperimmune serum protected mice from HSV-1 infection, we hypothesized that CD40 ligand (CD40L), which induces B-cell maturation, would protect mice from HSV-1 infection. CD40L-treated GVHD mice showed elevated IgG2a levels and increased survival compared with vehicle-treated transplant recipients.

Detection of rare apoptotic T cells in vivo.

The flow cytometric analysis of apoptosis in lymphocytes from in vivo samples has been difficult because of the low frequency of apoptotic events. To overcome this obstacle, many investigators have relied on in vitro incubations to increase the number of apoptotic cells before analysis. In this report, we show that an adaptation of the terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-digoxigenin nick-end labeling (TUNEL) assay for use in flow cytometry can be used to detect rare apoptotic lymphocytes from freshly harvested LN suspensions. This approach is both specific and extremely sensitive. This method also is amenable to multiparameter analyses and allows a phenotypic analysis of these rare apoptotic cells. However, we observed that some monoclonal antibodies can stain apoptotic-but not viable-cells nonspecifically. Therefore, the specificity of all antibodies to stain apoptotic cells was confirmed in competition assays.

A role for transforming growth factor-beta1 in the increased pneumonitis in murine allogeneic bone marrow transplant recipients with graft-versus-host disease after pulmonary herpes simplex virus type 1 infection.

To gain further insights in the pathogenesis of herpesvirus pneumonia in allogeneic bone marrow transplant recipients, transplanted mice (B10.BR --> CBA) with graft-versus-host disease (GVHD) and control mice (transplanted mice without GVHD and normal CBA mice) were infected intranasally with herpes simplex virus type 1 (HSV-1). When compared with infected control mice, infected allogeneic transplant recipients with GVHD showed increased periluminal mononuclear cell infiltrates. However, infected allogeneic transplant recipients with GVHD showed lower virus content in the lung tissue than infected control mice. High concentrations of transforming growth factor-beta 1 (TGF-beta1) were detected in the bronchoalveolar lavage (BAL) fluid of mock-infected allogeneic transplant recipients with GVHD, which increased slightly after infection. Anti-TGF-beta treatment of allogeneic transplant recipients with GVHD significantly decreased the histological evidence of pneumonitis at day 4 after HSV-1 infection. We conclude that allogeneic transplant recipients with GVHD have (1) increased pneumonia, (2) highly elevated levels of TGF-beta1 in the BAL fluid, and (3) reduced pulmonary virus content after HSV-1 infection. Our data suggest that the newly recognized dysregulation of cytokine (TGF-beta1) production may be more important than the viral load for the increased severity of HSV-1 pneumonia in allogeneic transplant recipients with GVHD.

Oligomerization of p53 is necessary to inhibit its transcriptional transactivation property at high protein concentration.

We have previously shown that transactivation by tumor suppressor protein p53 can be inhibited in vivo at elevated protein concentrations. In this study we characterize the structural requirements of this function. We show that oligomerization domain of p53 is involved in loss of transactivation at high protein concentrations: mutants not able to oligomerize are neither able to suppress transactivation, although these transactivating properties can be untouched.

Tacrolimus (FK506) increases neuronal expression of GAP-43 and improves functional recovery after spinal cord injury in rats.

Tacrolimus (FK506), a widely used immunosuppressant drug, has neurite-promoting activity in cultured PC12 cells and peripheral neurons. The present study investigated whether tacrolimus affects the expression of the neuronal growth-associated protein, GAP-43, as well as functional recovery after photothrombotic spinal cord injury in the rat. In injured animals receiving tacrolimus, the number of neurons expressing GAP-43 mRNA and protein approximately doubled compared to that in injured animals receiving vehicle alone. This increase in GAP-43-positive cells was paralleled by a significant improvement in neurological function evaluated by open-field and inclined plane tests. Another FKBP-12 ligand (V-10,367) had similar effects on GAP-43 expression and functional outcome, indicating that the observed effects of tacrolimus do not involve inhibition of the phosphatase calcineurin. Thus, tacrolimus, a drug which is already approved for use in humans, as well as other FKBP-12 ligands which do not inhibit calcineurin, could potentially enhance functional outcome after CNS injury in humans.

Experimental autoimmune myasthenia gravis in B10.BV8S2 transgenic mice: preferential usage of TCRAV1 gene by lymphocytes responding to acetylcholine receptor.

Multiple TCRBV genes have been implicated in experimental autoimmune myasthenia gravis (EAMG) pathogenesis in susceptible H-2(b) strains of mice. We studied the contribution of specific TCRBV and AV genes in EAMG pathogenesis using B10.BV8S2 transgenic mice (H-2[b]). The TCR transgenic mice predominantly have TCRBV8S2 transgene, but can use any of the endogenous AV gene repertoire. The transgenic mice were immunized with acetylcholine receptor (AChR) in CFA and evaluated for EAMG pathogenesis. Although the lymphocyte responses to AChR in B10.BV8S2 transgenic and nontransgenic TCR wild-type mice were equivalent, a marked reduction in lymphocyte response to the dominant AChR alpha chain peptide 146-162 was observed in the TCR transgenic mice. After boosting with AChR in CFA, anti-AChR Abs were detected in the serum, and 14 of 42 (33%) of the TCR transgenic mice developed clinical EAMG. Furthermore, EAMG in TCR transgenic mice was prevented by treatment with mAb to TCRBV8, which depleted BV8-expressing T cells. Cloning and sequencing of TCRAV genes from AChR-reactive T cells from B10.BV8S2 transgenic mice revealed a pattern of restricted TCRAV gene usage. The majority (60%) of the clones sequenced showed a sequence identical with that of the TCRAV1S8 gene. In the normal spleen cells of TCR transgenic mice, AV gene usage was more random. Thus, despite the presence of a complete endogenous TCRAV repertoire in B10.BV8S2 transgenic mice, T cells responding to AChR preferentially used a single endogenous TCRAV gene, thus implicating the involvement of the TCRAV1S8 gene in EAMG pathogenesis.

High-dose cyclophosphamide, carmustine, and etoposide with autologous transplantation in Hodgkin's disease: a prognostic model for treatment outcomes.

PURPOSE: To identify clinical factors predictive of treatment outcome after high-dose chemotherapy (HDC) for Hodgkin's disease and to develop a prognostic model for progression-free and overall survival. PATIENTS AND METHODS: 102 patients with relapsed or refractory Hodgkin's disease were treated with high-dose cyclophosphamide, carmustine, and etoposide and autologous marrow and/or peripheral blood progenitor cell support. Median follow-up of survivors is 4.1 years (1.8-7.5 years). Factors potentially important for treatment outcome were examined in univariate analysis, and Cox regression with forward selection was performed. A prognostic model was developed. RESULTS: Poorer progression-free and overall survival were associated with nodular sclerosis histology, abnormal performance status, progressive disease at HDC, more than one extranodal site of disease, and shorter time from initial diagnosis to HDC. These factors and the presence of B symptoms at relapse also predicted for decreased overall survival. Progressive disease immediately prior to HDC, more than one extranodal disease site, and abnormal performance status retained significance for both progression-free and overall survival in multivariate analysis. Progression-free and overall survival are 42% (95% confidence interval, CI, 34 to 53) and 65% (95% CI 54 to 73) at three years. A model based on number of risk factors present divides patients into low, intermediate, and high risk groups with three-year actuarial survival of 82%, 56%, and 19% respectively. Treatment outcome for patients treated with HDC at first chemotherapy relapse was not significantly different from that of the group overall (p > 0.3). CONCLUSIONS: Asymptomatic patients with Hodgkin's disease involving at most one extranodal site whose disease is controlled by conventional dose chemotherapy or radiation therapy at the time of HDC have good outcomes after this therapy. Presence of increasing numbers of risk factors are associated with poorer outcomes. Results of HDC compare favorably to those of standard dose salvage therapy. These data can be used to estimate likely outcomes in patients undergoing HDC for Hodgkin's disease, to identify potential candidates for innovative therapies, and to evaluate strategies for the optimal use of HDC in Hodgkin's disease.

Suppression of herpes simplex virus type 1 (HSV-1)-induced pneumonia in mice by inhibition of inducible nitric oxide synthase (iNOS, NOS2).

Intranasal Herpes simplex virus type 1 (HSV-1) infection of mice caused pneumonia. Manifestations of the disease included: histological pneumonitis, pulmonary influx of lymphocytes, decreased pulmonary compliance, and decreased survival. Immunohistochemical staining demonstrated iNOS induction and the nitrotyrosine antigen in the lungs of infected, but not uninfected mice, suggesting that nitric oxide contributes to the development of pneumonia. To elucidate the role of nitric oxide in the pathogenesis of HSV-1 pneumonia, infected mice were treated either with the inhibitor of nitric oxide synthase activity, N(G)-monomethyl-L-arginine (L-NMMA), or, as a control, with PBS or D-NMMA. L-NMMA treatment decreased the histological evidence of pneumonia and reduced the bronchoalveolar lavage lymphocyte number to one-quarter of the total measured in control-treated mice. L-NMMA treatment significantly improved survival and pulmonary compliance of HSV-1-infected mice. Strikingly, the L-NMMA-mediated suppression of pneumonia occurred despite the presence of a 17-fold higher pulmonary viral titer. Taken together, these data demonstrated a previously unrecognized role of nitric oxide in HSV-1-induced pneumonia. Of note, suppression of pneumonia occurred despite higher pulmonary virus content; therefore, our data suggest that HSV-1 pneumonia is due to aspects of the inflammatory response rather than to direct viral cytopathic effects.

Bone marrow transplantation for therapy-related myelodysplasia: comparison with primary myelodysplasia.

Therapy-related myelodysplasia (MDS) is a fatal marrow disorder distinct from primary MDS. We examined the efficacy of bone marrow transplantation (BMT) as a treatment for patients with therapy-related MDS. Eighteen patients with therapy-related MDS and twenty-five patients with primary MDS received an allogeneic, syngeneic, or unrelated donor BMT. Graft-versus-host disease prophylaxis included methotrexate, methotrexate plus cyclosporine, FK-506, or T cell depletion. Conditioning regimens consisted of cyclophosphamide/total body irradiation, with and without cytosine arabinoside, busulfan/cyclophosphamide, and cyclophosphamide/etoposide/carmustine. For patients with therapy-related MDS, the median age was 32 years and the actuarial disease-free survival was 24% (95% confidence interval 6, 42%) with a median follow-up of 3 years. For patients with primary MDS, the median age was 36 years and the actuarial disease-free survival at 3 years was 43% (95% confidence interval 22, 64%). Four of the therapy-related patients and two of the primary patients have relapsed. Three patients experienced graft failure; all three had received T cell-depleted marrow and two had marrow fibrosis. Our results suggest that patients with therapy-related MDS can be successfully transplanted. Transplantation should be considered early in the disease, since long-term disease-free survival is achievable.

Restriction of the TCR repertoire inhibits the development of memory T cells and prevents autoimmunity in lpr mice.

The lpr mutation, a disruption of the fas gene, induces spontaneous autoimmunity characterized by high titers of autoantibodies, lymphadenopathy, autoreactive T cells, and early mortality. The mechanism of autoimmunity, however, remains unknown. The driving force for disease could result from the T cell recognition of autoantigen or, alternatively, an intrinsic T cell defect that promotes autoreactivity. We investigated the role of antigen-TCR interaction in the pathogenesis of lpr autoimmunity by transferring the DO-11.10 TCR beta-chain transgene (Vbeta8.2-Dbeta1.1-Jbeta1.1) to the MRL-lpr/lpr background producing the MRL-lprbeta strain. Our results show that the MRL-lpr beta transgenic strain has increased survival, lower titers of autoantibodies, and decreased lymphadenopathy compared with nontransgenic littermates. These beneficial effects were associated with decreased expansion of CD4+ T cells expressing memory phenotypes (CD44+, CD45RB-, and LECAM-) in the transgenic compared with nontransgenic strains. A role for impaired recognition of autoantigen by T cells expressing the TCR transgene was suggested by comparing the phenotypes of Vbeta8.2+ (transgene+) vs Vbeta8.2- (transgene-) CD4+ T cells within the transgenic mice. These experiments show that Vbeta8.2- T cells, which express endogenously rearranged TCR, are the major contributors to the expansion of memory T cells in the transgenic mice. In contrast, T cells with memory phenotypes expand similarly in both the Vbeta8.2+ and Vbeta8.2- subsets of nontransgenic mice. Based on these results, we hypothesize that TCR recognition of autoantigen is a major contributor to autoimmunity in lpr mice and that T cells expressing a memory phenotype are perpetrators of this process.

TCR-beta transgenic mice fail to mediate a GVHR due to defects of allorecognition and subsequent IL-2 generation.

All T cells of TCR-beta transgenic mice bear a single TCR-beta chain and consequently the diversity of the TCR may be reduced by as much as one million-fold. Despite this limited diversity, many measures of lymphocyte function in these mice are normal. We have previously demonstrated that lymphoid cells from TCR-beta mice are unable to mediate an intense graft-versus-host response (GVHR). In order to investigate the mechanism of this hyporesponsiveness, we studied in vivo allorecognition in diverse strains of TCR-beta mice. All tested strains of TCR-beta mice failed to mediate a substantial GVHR across multiple H-2 barriers. In addition, mixtures of cells from several strains of TCR-beta mice only generated mild GVHRs. Sensitive tests of in vitro allorecognition show that lymphoid cells from TCR-beta mice respond less vigorously to alloantigen as measured both by decreased proliferation and decreased IL-2 production in a MLR. In addition, cells from TCR-beta mice fail to use exogenous IL-2 appropriately in their response to alloantigen. We conclude that the fixed TCR-beta chain causes a defective response to alloantigen, which is measured as decreased IL-2 generation and utilization, and that this abnormality results in a decreased GVHR.

V beta 8.2 transgene expression interferes with development of experimental autoimmune thyroiditis in CBA k/q but not k/k mice.

The thyroiditogenic T cell receptor (TCR) repertoire is not yet well defined in murine experimental autoimmune thyroiditis (EAT). Our recent work has shown that, while V beta 8+ T cells have no major role in EAT induction with mouse thyroglobulin (MTg), V beta 13 may be involved. To examine the effect of skewing the TCR repertoire on EAT development, CBA (H2k) mice were mated with B10.Q mice harboring an ovalbumin-specific V beta 8.2 TCR transgene (trg), and the trg+ mice were backcrossed to CBA. FACS analysis showed that peripheral blood T cells from trg+ mice had about 76 and 90% V beta 8.2+ cells in the CD4+ and CD8+ subsets, respectively, compared with about 15 and 11% in trg- sibs. The transgenic CBA k/k and k/q mice were immunized with MTg and sacrificed 28 days later. In all trg+ mice, anti-MTg titers and T cell proliferative responses to MTg were significantly lowered. However, thyroid infiltration was distinctly different in the two strains of transgenic mice; a significant decrease was seen primarily in k/q, but not k/k, trg+ mice. Thus, skewing the TCR repertoire to overexpress an irrelevant TCR revealed the possession of a less flexible thyroiditogenic TCR repertoire in k/q, but not k/k, mice.

Plasticity of the T cell receptor repertoire in TCR beta-chain transgenic mice.

The potential alpha beta T cell receptor (TCR) repertoire in normal mice is extremely large and estimated by M. M. Davis and P. J. Bjorkman (Nature 334, 395, 1988) to include 5.2 x 10(18) different receptor molecules. This tremendous diversity provides the basis for T cell recognition of the universe of antigens including bacterial, viral, and allogeneic epitopes. Expression of a single TCR beta-chain transgene should alter the repertoire by limiting the available diversity, therefore, creating holes in the repertoire or producing TCR with decreased affinity. To determine the effect of drastically decreasing the size of the repertoire, we investigated T cell responses in TCR beta-chain transgenic mice expressing the V beta 8.2 transgene. Previous results showed that > 98% of T cells in these mice express the transgene; thus, the TCR repertoire is reduced by orders of magnitude. We tested the T cell responses of the transgenic mice and nontransgenic littermates to nine different MHC haplotypes in mixed lymphocyte reactions, five protein antigens, and eight immunogenic peptides. Surprisingly, the transgenic mice responded to all antigenic stimuli tested indicating the lack of a hole in the TCR repertoire. Interestingly, however, the response in every case was quantitatively lower than the response by the nontransgenic littermates. In contrast, transgenic and nontransgenic T cells responded equivalently to stimulation with mitogens or to stimulation with immobilized alpha-TCR mAb indicating that the transgenic T cells had a normal capacity to respond. To differentiate between decreased TCR affinity and decreased precursor frequency, we performed a limiting dilution analysis to the peptide antigens CI:NP and OVA324-339. The results showed approximately a three-to eight-fold decrease in the frequency of transgenic T cells responding to the peptide compared to nontransgenic littermates. We previously showed that the response to cI84-98 and PLP could be blocked with anti-V beta 8 mAb indicating that V beta 8.2-bearing T cells are capable of responding to peptide antigen. Analysis of TCR V alpha chain expression by PCR and flow cytometry showed similar V alpha expression in both the transgenic and the nontransgenic mice. These results demonstrate tremendous plasticity in the TCR repertoire permitting T cell responses by the transgenic mice to all antigens tested. However, the decreased magnitude of the responses may impair the capacity to defend against natural pathogens. Therefore, although the large TCR repertoire of normal mice may not be necessary to produce in vitro responses to many experimental antigens, it may confer survival benefits in natural environments.

Expression of an ovalbumin-specific V beta 8.2 TCR transgene inhibits collagen arthritis in B10.Q mice.

Previous studies have illustrated the importance of T cells bearing alpha beta TCRs in the induction and development of collagen induced arthritis (CIA) in mice. However, the scope of TCR usage in CIA has yet to be clearly defined. Given the inherent diversity of the TCR repertoire, the relative flexibility of the arthritogenic TCR repertoire specific for type II collagen (CII) is not clear. Therefore, we chose to examine the influence of a highly skewed TCR repertoire on CIA. Arthritis susceptible B10.Q (H-2q) mice were mated with C57L (H-2b) animals expressing an ovalbumin-specific V beta 8.2 TCR transgene (Tg) and Tg+ offspring were further backcrossed to B10.Q. Homozygous H-2q/q, V beta 8.2 Tg+ mice displayed a high level of V beta 8.2+ T cells in peripheral blood. However, expression of some endogenous V beta TCR, such as V beta 14, was still detected. Upon immunization with bovine CII in adjuvant, V beta 8.2 Tg+ mice were highly resistant to CIA when compared with Tg- littermates. Analysis of sera demonstrated a marked reduction in antibody specific for homologous mouse CII as well as heterologous bovine CII in Tg+ animals. Interestingly, V beta 8.2 Tg+ mice still mounted good antibody responses following immunization with human thyroglobulin, indicating that the skewed TCR repertoire affected anti-CII but not antithyroglobulin responses. Thus, our findings show that constraints placed on the TCR repertoire inhibit pathogenic responses against CII and suggest that in H-2q mice the arthritogenic TCR repertoire bears only limited flexibility.

T cell receptor (beta chain) transgenic mice have selective deficits in gamma delta T cell subpopulations.

TCR-beta (T cell receptor-beta chain) transgenic mice have altered lymphocyte development. TCR-beta transgenic mice are hyporesponsive to alloantigens in vivo and are deficient in gamma delta T cells. In order to begin a study of the relationship between a deficiency of alloreactive gamma delta cells and the defective function of in vivo alloantigen recognition, we analysed the gamma delta T cell development in TCR-beta mice. The presence of the TCR-V beta 8.2 chain transgene is associated with inhibition of gamma chain gene rearrangement. In order to determine how the presence of the TCR-beta transgene affects gamma delta T cell development, gamma delta T cells were studied in the skin, intestine and spleen. TCR-beta mice have dramatically reduced numbers of gamma delta T cells in the spleen and moderately reduced numbers of gamma delta T cells among intestinal intraepithelial lymphocytes. In contrast, these mice have normal numbers of gamma delta dendritic epidermal cells (DEC). These selective deficits could be due to the developmental regulation of transgene transcription during fetal life. We examined transcription of the TCR-beta transgene in the fetal thymus and found that the TCR-beta transgene is first transcribed at high levels on day 16 of fetal life, after DEC have already migrated from the thymus to the epidermis. Furthermore, mRNA from the transgene was detected in DEC, ruling out the formal possibility that DEC bear a gamma delta receptor only because they are incapable of expressing the transgene.(ABSTRACT TRUNCATED AT 250 WORDS)