Flow cytometric analysis and immunohistochemistry of delayed-type hypersensitivity responses in mice immunized with rat hepatocytes

Delayed-type hypersensitivity (DTH) responses to rat hepatocytes (HCs) in mice were investigated by flow cytometric analysis and immunohistochemistry with monoclonal antibodies directed against murine class II, CD4, and CD8 antigens. Mice were immunized subcutaneously (s.c.) with 10(6) rat HCs (referred to as s.c.-immunized mice), and control mice were injected s.c. with sterile Hanks' solution (non-immunized mice). Four days later, 10(5) rat HCs were injected into the footpad of s.c.-immunized mice and non-immunized mice. The DTH response in s.c.-immunized mice significantly increased after challenge when compared to that in non-immunized mice. The numbers of class II+, CD4+, and CD8+ cells in the footpad, and CD4+ and CD8+ cells in the inguinal lymph node of s.c.-immunized mice significantly increased during the DTH response. An increase in the number of CD4+ cells in the footpad of s.c.-immunized mice after challenge was more significant than that of non-immunized mice. The number of CD4+ cells increased more markedly in the footpad of s.c.-immunized mice as compared to that of CD8+ cells. Furthermore, immunohistochemical studies of the footpad of s.c.-immunized mice showed more severe infiltration of CD4+ cells rather than CD8+ cells at the injection site of rat HCs. These results suggest that the DTH response in the footpad of mice immunized with rat HCs is associated with severe infiltration of CD4+ cells.

Clonal CD3+CD8+ large granular lymphocyte (LGL)/NK-associated (NKa) expansions: primary malignancies or secondary reactive phenomena?

This study reports the clinical, haematological and immunophenotypic features of a series of 25 patients with clonal expansions of large granular lymphocytes (LGL)/NK-associated (NKa) cells. These showed a male predominance (16:9) with a median age of 67 (range 38-91) years; four had a documented history of rheumatoid arthritis, a further 18 had diverse clinical disorders, and the remaining three were clinically well. Mild anaemia was found in approximately half the patients and a lymphocytosis (seen in approximately 70% of the cases) was usually modest (< 10.0 x 10(9)/l). Neutropenia was the most frequently observed feature, and this was typically persistent in nature. Serum studies revealed few consistent features although positive rheumatoid factor and increased soluble CD8 levels were noted in 67% and 87% of those cases tested. Phenotypically, all cases were CD2+CD3+CD8+ and expressed membrane TCR alpha beta chains; most (17/22) were additionally CD5+ and (19/22) CD7+. The staining intensities of CD5 and CD7 antigens were however lower than that of normal CD4+ and CD8+ blood lymphocytes. Expression of NKa antigens was variable although 16/22 cases were CD16+CD56- and 19/22 were CD57+. Clonal CD3+CD8+ LGL/NKa expansions with a CD16+CD56+ composite phenotype were not seen in this patient series. Analyses of 'activation' antigens showed a consistent lack of CD25 expression by CD3+ cells, but increased CD3/Ia co-expression was found in a high proportion (19/25) of cases. Studies of CD45R isoform expression by CD8+ LGL/NKa cell fractions revealed a consistent CD45RA+RO- profile for all cases tested.(ABSTRACT TRUNCATED AT 250 WORDS)

Combined effects of FK506 (tacrolimus) and cyclophosphamide on atypical B220+ T cells, cytokine gene expression and disease activity in MRL/MpJ-lpr/lpr mice

Groups of female MRL/MpJ-lpr/lpr mice received either saline or FK506 (tacrolimus; 2 mg/kg intraperitoneally) three times weekly, cyclophosphamide (CY; 20 mg/kg) once monthly, or both drugs from 8 weeks of age. Median survival for untreated and CY-treated mice was 26 weeks, and for FK506- and FK506 + CY-treated groups was > or = 44 weeks. Severity of skin lesions and lymph node hyperplasia was markedly reduced by the drug combination, whereas either drug alone was less effective. FK506 or CY alone delayed the onset of proteinuria, but by 24 weeks all of these animals were positive. In contrast, drug combination reduced the prevalence of proteinuria to < or = 60% throughout the 44 weeks of study. Sequential monitoring of peripheral blood lymphocytes revealed that combination therapy but not monotherapy markedly reduced the proportion of atypical CD3+ B220+ and CD3+CD4-CD8- T cells. Neither FK506 nor CY affected the reduction in IL-2 and IL-4 mRNA levels observed in lymph nodes of diseased animals compared with normals. Although the drug combination also did not affect IL-2 mRNA levels, IL-4 mRNA transcripts were increased six-fold compared with saline-treated controls. IL-10 and interferon-gamma (IFN-gamma) mRNAs were induced by FK506, CY and by the drug combination. Serum levels of anti-dsDNA antibodies were reduced in all treatment groups. These data demonstrate improved efficacy of combined T and B cell-directed immunosuppression in murine lupus, associated with marked inhibition of atypical T cells and selective augmentation of IL-4 within the affected lymphoid tissue.

CD8+ T cells suppress human immunodeficiency virus replication by inhibiting viral transcription

CD8+ cells from human immunodeficiency virus (HIV)-infected individuals suppress HIV replication in cultured CD4+ cells by a noncytolytic mechanism that involves a secreted CD8(+)-cell antiviral factor (CAF). The results of this study suggest that CD8+ cells, as well as CAF, arrest HIV replication at the level of viral transcription. Culturing naturally infected CD4+ cells actively producing HIV with autologous CD8+ cells or a 50% dilution of culture fluids from these cells results in a > 80% reduction in the number of cells expressing HIV antigens and RNA. This effect was observed within 2 days after exposure to CD8+ cells but required 6 days in the presence of CAF-containing culture fluids to reach the same extent of HIV suppression. Northern blot analysis of CD4+ cell extracts revealed that all viral RNA species (unspliced and single and double spliced) were reduced in quantity to a similar extent. CAF-containing culture fluids also had a direct inhibitory effect on HIV long terminal repeat (LTR)-driven transcription in HIV-infected 1G5 cells carrying an LTR-luciferase construct. Suppression of basal levels of LTR-driven transcription was not detected. Thus, the results suggest that the noncytolytic CD8+ cell antiviral activity observed in HIV infection exerts its effects, at least in part, by specifically interrupting HIV transcription. These findings could help in developing therapies for HIV infection.

Transgenic expression of interleukin 7 restores T cell populations in nude mice

The thymic lesion of the nude mouse causes a profound block in T cell development. The failure of most T cells to mature in nude mice is likely to reflect a requirement for signals elaborated in the normal thymus. Interleukin 7 (IL-7), a lymphokine that is normally expressed in the thymus and has been implicated in T cell maturation, might be central to this process. To test this possibility, we introduced a transgene directing lymphoid expression of IL-7 into nude mice and found that it substantially alleviates the block in T cell maturation caused by the thymic defect. IL-7 transgenic nude mice have increased numbers of peripheral cells expressing the T cell marker Thy-1, the T cell antigen receptor complex, and the co-receptors CD4 and CD8. The IL-7 transgene also restores T cell-specific proliferation and activation responses to the peripheral cells of transgene-rescued nude mice. Such findings point toward a fundamental role for IL-7 in the thymic maturation of T cells.

Development of CD4+CD8+ thymocytes in RAG-deficient mice through a T cell receptor beta chain-independent pathway

Antigen-binding diversity is generated by site-specific V(D)J recombination of the T cell receptor (TCR) and immunoglobulin loci in lymphocyte precursors. Coordinate expression of two structurally distinct recombinase activating genes, RAG-1 and RAG-2, is necessary for activation of site-specific V(D)J recombination. In mice bearing targeted disruptions of either the RAG-1 or RAG-2 genes, T and B lymphocyte development is arrested at the CD4-8- double negative (DN) thymocyte or B220+/CD43+ pro-B cell stage. Development of CD4+CD8+ double positive (DP) thymocytes is restored by expression of a functionally rearranged TCR beta transgene, suggesting that TCR beta expression is critical for this developmental transition. We have found that treatment of adult or newborn RAG-deficient mice with a single sublethal dose of gamma-irradiation rescues the DN to DP transition in early thymocytes, and this is accompanied by a dramatic increase in thymus cellularity. In contrast to the observed induction of thymocyte maturation, there was no phenotypic or functional evidence of coincident B lymphocyte development in irradiated RAG-deficient mice. Interestingly, maturation of DP thymocytes occurred without expression of TCR beta protein in the cytoplasm or on the cell surface. These results suggest an in vivo pathway for DP thymocyte development which is TCR beta chain independent.

Monoclonal expansion of large granular lymphocytes with a CD4+ CD8dim+/- phenotype associated with hairy cell leukemia

Peripheral blood lymphoid cell expansions with an unusual CD3+, CD4+, CD8dim+/-, CD11b+, CD57+ immunophenotype have recently been reported. They frequently have the morphology of large granular lymphocytes (LGL) and can be either monoclonal or polyclonal. Their significance is still unclear and no association with hematological neoplasms has been described. We report the case of a patient with a monoclonal expansion of LGL associated with a B-cell-derived hairy cell leukemia. The two lymphoid clones were not physically associated since T-LGL were found in the peripheral blood and hairy cells were detected in the bone marrow and kidney.

Immunohistochemical detection of T-cell subsets and other leukocytes in paraffin-embedded rat and mouse tissues with monoclonal antibodies

We describe a method for immunohistochemical localization of T-cells, CD4+ T-cells, CD8+ T-cells, B-cells, activated lymphocytes, major histocompatibility complex (MHC) class II antigens, macrophages, dendritic cells, and granulocytes in rat and mouse tissue fixed in periodate-lysine-paraformaldehyde (PLP) and embedded in paraffin. Rat and mouse spleen and eyes were fixed in PLP for 18-24 hr, rapidly dehydrated, infiltrated under vacuum with paraffin at 54 degrees C, sectioned, and stained with appropriate monoclonal antibodies (MAbs). Sections of PLP-fixed, paraffin-embedded spleen were compared with acetone-fixed frozen spleen sections with respect to morphology and staining quality. Nine of 10 MAbs to rat antigens and eight of nine MAbs to mouse antigens stained paraffin sections equally or more intensely than frozen sections. The two MAbs that showed weaker staining still gave good staining on paraffin sections. Paraffin-embedded rat and mouse eyes were easier to section serially than frozen eyes, showed superior morphology, and individually stained cells were readily identified. Therefore, a combination of PLP fixation and low-temperature paraffin embedding permits detection of the major types of immune cell in rat and mouse tissues while maintaining good morphology, particularly in diseased, damaged, or delicate tissues.

T cell receptor-mediated signaling events in CD4+CD8+ thymocytes undergoing thymic selection: requirement of calcineurin activation for thymic positive selection but not negative selection

The goal of this study was to identify the differences of intracellular signals between the processes of thymic positive and negative selection. The activation of calcineurin, a calcium- and calmodulin-dependent phosphatase, is known to be an essential event in T cell activation via the T cell receptor (TCR). The effect of FK506, an inhibitor of calcineurin activation, on positive and negative selection in CD4+CD8+ double positive (DP) thymocytes was examined in normal mice and in a TCR transgenic mouse model. In vivo FK506 treatment blocked the generation of mature TCRhighCD4+CD8- and TCRhighCD4-CD8+ thymocytes, and the induction of CD69 expression on DP thymocytes. In addition, the shutdown of recombination activating gene 1 (RAG-1) transcription and the downregulation of CD4 and CD8 expression were inhibited by FK506 treatment suggesting that the activation of calcineurin is required for the first step (or the very early intracellular signaling events) of TCR-mediated positive selection of DP thymocytes. In contrast, FK506-sensitive calcineurin activation did not appear to be required for negative selection based on the observations that negative selection of TCR alpha beta T cells in the H-2b male thymus (a negative selecting environment) was not inhibited by in vivo treatment with FK506 and that there was no rescue of the endogenous superantigen-mediated clonal deletion of V beta 6 and V beta 11 thymocytes in FK506-treated CBA/J mice. DNA fragmentation induced by TCR activation of DP thymocytes in vitro was not affected by FK506. In addition, different effects of FK506 from Cyclosporin A on the T cell development in the thymus were demonstrated. The results of this study suggest that different signaling pathways work in positive and negative selection and that there is a differential dependence on calcineurin activation in the selection processes.

Upregulation of cytokines associated with macrophage activation in the Lewis-to-F344 rat transplantation model of chronic cardiac rejection

Lewis-to-F344 rat cardiac allografts develop chronic rejection and arteriosclerotic lesions rich in mononuclear cells (especially macrophages). This study was performed to determine whether cytokine pathways associated with macrophage activation are upregulated in hearts undergoing chronic rejection. Gene transcript levels for IFN-gamma, monocyte chemoattractant protein-1 (MCP-1), and IL-6 were measured with reverse-transcription PCR assays optimized for each gene. Gene products were confirmed by immunohistology. For all three genes, transcript levels in rat cardiac allografts increased significantly on day 7 and remained elevated on days 14 and 28 posttransplantation, as compared with naive hearts, paired host hearts, and syngrafts (P < 0.006). For the inducible genes IFN-gamma and MCP-1, high transcript levels in cardiac allografts were in contrast with low levels in host spleens. On the other hand, transcript levels for the basally expressed gene IL-6 were elevated in both organs. Immunostaining confirmed allograft-specific expression for all three cytokines and localized the gene products to infiltrating mononuclear cells in the interstitium and vasculature. The sustained expression of these cytokines in cardiac allografts undergoing chronic rejection supports the widely held hypothesis that the intimal changes associated with transplant arteriosclerosis are mediated by cellular activation and cytokine production.

Focal expression of interleukin-2 does not break unresponsiveness to "self" (viral) antigen expressed in beta cells but enhances development of autoimmune disease (diabetes) after initiation of an anti-self immune response

The participation of IL-2 in insulin-dependent (type 1) diabetes (IDDM) was analyzed in transgenic (tg) mice expressing the nucleoprotein (NP) of lymphocytic choriomeningitis virus and IL-2 under control of the rat insulin promoter focally in beta cells of the islets of Langerhans. Insertion and expression of the viral (self) gene or of the IL-2 gene alone did not lead to IDDM. Infiltration primarily of CD4 and B lymphocytes and increased expression of MHC class I and II molecules occurred in islets where IL-2 was expressed. By contrast, neither cellular infiltrates nor expression of MHC class I or II glycoproteins above base levels was noted in tgs expressing the viral protein alone. Double tg mice expressing both the viral protein and IL-2 in their islets displayed a modest increase in incidence of spontaneous diabetes compared with that of single transgenic mice expressing IL-2 alone. Breaking of immunological unresponsiveness or sensitization to self antigens did not occur. Neither cytotoxic T lymphocytes (CTL) nor antibodies directed against the viral tg (NP) were generated. However, after challenge with lymphocytic choriomeningitis virus, double tg mice developed anti-self (viral) CTL and IDDM (incidence > 95%) within 2 mo. The generation of virus ("self")-specific MHC-restricted CTL was dependent on CD4+ help. In contrast, viral inoculum to single tg mice expressing either the viral protein or IL-2 failed to enhance the incidence of IDDM over 30% for viral protein or 10% for IL-2 after an 8-mo observation period. Hence, in this autoimmune model in situ expression of IL-2 did not break unresponsiveness but markedly enhanced ongoing disease.

High IL-4 production is a stable phenotype of CD8negCD45RAnegCD27neg T cells

CD27neg T cells are found only among CD4pos-CD45ROpos T cells and represent a T cell subset functionally distinct from CD27pos T cells. We examined CD4posCD45ROpos T cells that were sorted into CD27neg and CD27pos populations for their cytokine production in response to different activation pathways. We found that CD27neg T cells are characterized by high IL-4 and low IL-2 production, regardless of whether the cells were activated through CD3 plus CD28, CD2 plus CD28, or PHA plus PMA. However, subpopulation-specific patterns of cytokines were the clearest demonstrable following CD2 plus CD28 stimulation. We conclude from these data that high IL-4 production is a stable phenotype of CD27neg T cells.

T cell receptor gamma delta repertoire is skewed in cerebrospinal fluid of multiple sclerosis patients: molecular and functional analyses of antigen-reactive gamma delta clones

To study the relevance of gamma delta T cells in multiple sclerosis (MS) we analyzed the T cell receptor (TCR) gamma delta repertoire and the antigen reactivity of gamma delta clones isolated from cerebrospinal fluid (CSF). In T cell cultures derived from CSF we found an increased percentage of V delta 1+ cells as compared to peripheral blood of the same donors. Phenotypic analysis of cells from MS CSF with V gamma- and V delta-specific monoclonal antibodies (mAb) showed that the V delta 1 chain is most frequently associated with gamma chains belonging to the V gamma 1 family. Sequence analysis of TCR genes revealed heterogeneity of junctional regions in both delta and gamma genes indicating polyclonal expansion. gamma delta clones were established and some recognized glioblastoma, astrocytoma or monocytic cell lines. Stimulation with these targets induced serine esterase release and lymphokine expression characteristic of the TH0-like phenotype. Remarkably, these tumor-reactive gamma delta cells were not detected in the peripheral blood using PCR oligotyping, but were found in other CSF lines independently established from the same MS patient. Altogether, these results demonstrate that in the CSF there is a skewed TCR gamma delta repertoire and suggest that gamma delta cells reacting against brain-derived antigens might have been locally expanded.

Mouse thymus dendritic cells: kinetics of development and changes in surface markers during maturation

The early thymus precursor population of adult mice has the capacity to generate T cells, B cells and dendritic cells (DC). These precursors were injected into the thymus of irradiated recipients in order to follow the kinetics of thymic DC development. The resultant cohort of T-lineage cells developing in the thymus was accompanied by a parallel cohort of DC, present at 10(3)-fold lower frequency. The intrathymic lifespan of these DC was as short as that of T-lineage thymocytes. As the thymic DC matured, some markers characteristic of the original precursor population gradually declined (Ly-5, c-kit, Sca-2) whereas markers characteristic of thymic DC appeared and were maintained (major histocompatibility complex class II, CD11c, NLDC-145 and CD8 alpha). Some thymic DC expressed the early B-cell marker BP-1, and BP-1 mRNA, throughout their maturation. The surface markers on thymic DC could be divided into two groups. Some markers, including class I and class II MHC, CD8 alpha and BP-1, appeared to be integral components of the DC surface. In contrast, other markers, including Thy-1, CD4 and CD8 beta, had probably been picked up from associated thymocytes.

Lymphocyte subpopulations and concentrations of soluble CD8 and CD4 antigen after anaerobic training

In 13 middle-aged, moderately trained men (40-60 yr) we investigated the influence of anaerobic training on immunological parameters measured at rest. The 4 week anaerobic training program (two 30-min sessions weight lifting and one interval training per week; lactate levels 4-6 mM and 8-10 mM, respectively), caused a significant increase of the mean arm muscle force by 7% (handgrip test, p < 0.05). Evaluation of lymphocyte subsets was performed by means of three-colour immunofluorescence analysis (FACS). After 4 weeks of training we found a significant reduction of the CD4+ T-cell counts by 15% (p < 0.05) paralleled by a fall of naive cells (CD3+/CD4+/CD45RA+) by 16%, which, however, was statistically not significant. While percentages of CD3+ lymphocytes decreased significantly by 6% (p < 0.001), absolute numbers of CD3+ T-lymphocytes were not detectably affected and also the relative ratio of CD8+ T-cell subsets, i.e. the ratio of suppressor vs cytotoxic T-cells (CD3+/CD8+/CD11b+, CD3+/CD8+/CD11b- respectively) remained unchanged. Likewise the serum concentrations of the soluble CD8 and CD4 antigen (sCD8/sCD4) as determined by sandwich enzyme immunoassays were found to be unaffected. We conclude that 40-60 years old healthy human subjects performing anaerobic training experience on average a significant decrease of circulating CD4+ T-lymphocytes, while other parameters including the activation parameters sCD8 and sCD4 remained unchanged.

CD8+ dermal T cells from a sulphamethoxazole-induced bullous exanthem proliferate in response to drug-modified liver microsomes

There is evidence that T lymphocytes play a critical role in the pathogenesis of drug-induced bullous exanthems. Sulphonamides are known to be among the most frequent aetiological agents in these severe drug-induced cutaneous hypersensitivity reactions. Several studies indicate that cytochrome P450-dependent metabolites of sulphonamides act as the nominal allergens. A 70-year-old woman with a severe blistering exanthem caused by cotrimoxazole (sulphamethoxazole and trimethoprim) was studied. We employed an in vitro approach to determine whether cytochrome P450-dependent enzymes activated drug-specific T lymphocytes from this patient. Immunohistochemical analysis of involved skin revealed a majority of epidermal CD8+ T lymphocytes, whereas the dermal infiltrate was composed of both CD4+ and CD8+ T cells. Dermal T lymphocytes isolated from lesional skin proliferated in response to sulphamethoxazole, but not to trimethoprim, in the presence of autologous mononuclear cells used as antigen-presenting cells. The antigen-specific response of sulphamethoxazole-specific T cells was significantly augmented in the presence of murine liver microsomes with P450-dependent catalytic activities. Our observations suggest that some cutaneous hypersensitivity reactions to sulphamethoxazole are due to drug-specific T lymphocytes. Cytochrome P450-dependent enzymes may play a critical role in the formation of the nominal antigen, which is recognized by antigen-specific T cells.

Expression of cell interaction molecules by immature rat thymocytes during passage through the CD4+8+ compartment: developmental regulation and induction by T cell receptor engagement of CD2, CD5, CD28, CD11a, CD44 and CD53

Rat thymocytes of the T cell receptorlow (TcRlow) CD4+8+ subset which is the target of repertoire selection are heterogeneous with respect to expression of the cell interaction (CI) molecules CD2, CD5, CD11a/CD18 (LFA-1), CD28 and CD44. We show that this heterogeneity is due to the developmental regulation of these CI molecules during passage through the CD4+8+ compartment, and to up-regulation by TcR engagement. Thus, cohorts of CD4+8+ cells differentiating synchronously in vitro from their direct precursors, the immature CD4-8+ cells, were homogeneous with regard to CI molecule expression. Upon entry into the CD4+8+ compartment, they expressed relatively high levels of CD2 and CD44, and moderate levels of CD5, CD28 and CD11a. CD2, CD28 and CD44 were slightly down-regulated during the following 2 days, whereas CD5 slightly increased and CD11a remained constant. TcR stimulation using immobilized monoclonal antibodies resulted in rapid and dramatic up-regulation of CD2, CD5 and CD28 and, to a lesser extent, of CD11a and CD44. Finally CD53, a triggering structure absent from unstimulated CD4+8+ thymocytes was also rapidly induced by TcR stimulation. Inclusion of interleukin (IL)-2, IL-4, or IL-7 in this in vitro differentiation system did not affect the levels of CI molecules studied. Since the high levels of CI molecules induced by TcR-stimulation correspond to those found in vivo on TcRintermediate thymocytes known to be undergoing repertoire selection, these results suggest that upregulation of CI molecules by TcR engagement provides a mechanism by which thymocytes that have entered the selection process gain preferential access to further interactions with stromal and lymphoid cells in the thymus.

Absence of gluten-specific T lymphocytes in the skin of patients with dermatitis herpetiformis

Dermatitis Herpetiformis (DH) is an immunobullous skin disease with an associated gluten-sensitive enteropathy. Withdrawal of gluten from the diet leads to the resolution of both the skin lesions and the enteropathy. A T cell-mediated immune response to gluten has been implicated in the damage to the gut; the possible gluten specificity of the T cell infiltrate in DH skin lesions has not, however, been investigated. T cell lines (TCL) were therefore established from the skin lesions of eight patients with DH by culturing skin fragments for 11-17 days with a medium supplemented with 20 U/ml of IL-2. In three cases, gliadin (fraction of gluten toxic to the DH gut) and irradiated, autologous peripheral blood mononuclear cells were also added. The TCL were stained for CD3, CD4, CD8, TCR alpha beta and gamma delta expression by indirect immunofluorescence, and their proliferative responses to mitogens and gluten fraction III (a peptic-tryptic digest of gluten) investigated. Of the eight CD3+ TCL, four were predominantly CD4+ (82.1-98.8%), three predominantly CD8+ (92.6-98.6%) and one TCL contained both 87.6% CD4+ and 95.2% CD8+ T cells, a substantial proportion of which were presumably double-labelled CD4+, CD8+ T cells. All eight TCL, which were almost exclusively TCR alpha beta +, proliferated in response to PHA whilst six out of the eight were stimulated by Concanavalin A. None of the TCL proliferated to gluten fraction III alone; however, two TCL showed increased proliferation to the antigen in the presence of exogenous IL-2 or IL-4 (10 U/ml) compared to cytokine alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Encephalitogenic, myelin basic protein-specific T cells from naive rat thymus: preferential use of the T cell receptor gene V beta 8.2 and expression of the CD4-CD8- phenotype

Using a primary limiting dilution approach to generate T cell lines, we compared myelin basic protein (MBP)-specific T cell clones from naive unprimed Lewis rat thymuses with the corresponding T cell repertoire of primed rats. We found that in the native thymus repertoire MBP-specific, encephalitogenic T cell clones preferentially use T cell receptor V beta 8.2 genes, along with CDR3 sequences typical for the primed Lewis anti-MBP response. In contrast to T cells from primed immune organs, which all display the CD4+CD8- phenotype, the majority of naive thymus-derived T cell clones expressed reduced levels of the CD4 co-receptor. Some clones were completely CD4-CD8-, while others included CD4-CD8- subpopulations along with CD4+CD8- T cells. In the one mixed population examined in detail, the CD4-CD8- and CD4+CD8-T cell subpopulations used a T cell receptor with identical beta chain sequence. The data suggest that in the Lewis rat the biased T cell receptor gene usage by encephalitogenic T cells is a property of the natural thymic T cell repertoire, possibly as a consequence of positive selection. The unusually low expression of CD4 in the major histocompatibility complex class II-restricted autoreactive T cells could be related to their escape from negative selection within the thymus.

Programmed differentiation of murine thymocytes during fetal thymus organ culture

Fetal thymus organ culture (FTOC) has become widely used to investigate the impact of immunomodulators on T cell development. However, these studies have given variable results among different laboratories. In this study, we have found that fetal tissue age and mouse strain differences can affect the development of T cell phenotypes in this system. T cell development in FTOC occurred in two 'waves', defined as peaks of cell recovery. The first wave consisted initially of CD4-CD8- double negative (DN) cells and CD4-CD8+ single positive (SP) T cells expressing gamma delta T cell receptor (TCR). CD4+CD8+ double positive (DP) cells expressing low levels of alpha beta TCR were produced soon thereafter; and these cells dominated the cultures for the balance of the first wave. Prolonged FTOC resulted in the production of another wave of T cells which were relatively enriched for CD4 or CD8 SP cells expressing high levels of alpha beta TCR, as well as DN cells and CD4-CD8+ SP T cells expressing high levels of gamma delta TCR. As defined by cell number and differentiation of alpha beta TCR SP cells, development was delayed in FTOC using fetal thymus tissue from younger fetuses relative to that observed when older fetal thymus tissue was used. The degree of development of T cells in FTOC was also strain dependent. Organ cultures derived from 14 gestation days (gd) C.B-17 scid/scid fetal thymus did not generate TCR-bearing mature SP cells, but they did produce TCR-negative CD4 and CD8 SP cells likely to be precursors of DP thymocytes. Such cultures made from 18 gd tissue did not produce SP cells. Negative selection in FTOC was also evaluated. Mtv-specific V beta 3 cells were deleted in FTOC of C3H/HeN tissue. Deletion occurred only in late FTOC, suggesting a late encounter between the Mtv deleting elements and susceptible T cells during ontogeny. These results show that while FTOC recapitulates normal thymic development by a variety of criteria, results can be influenced by the length of culture, as well as by the age and strain of fetal thymus tissue utilized.

Constitutive activation of the Fas ligand gene in mouse lymphoproliferative disorders

Mice homozygous for lpr (lymphoproliferation) or gld (generalized lymphoproliferative disease) develop lymphadenopathy and splenomegaly and suffer from autoimmune disease. The lpr mice have a defect in a cell-surface receptor, Fas, that mediates apoptosis, while gld mice have a mutation in the Fas ligand (FasL). Northern hybridization with the FasL cDNA as probe indicated that the cells accumulating in lpr and gld mice abundantly express the FasL mRNA without stimulation. By means of in situ hybridization and immunohistochemistry, we identified the cells expressing the FasL mRNA as CD4-CD8- double negative T cells. The T cells from lpr mice were specifically cytotoxic against Fas-expressing cells. Since FasL is normally expressed in activated mature T cells these results indicate that the double negative T cells accumulating in lpr and gld mice are activated once, and support the notion that the Fas/FasL system is involved in activation-induced suicide of T cells. Furthermore, the graft-versus host disease caused by transfer of lpr bone marrow to wild-type mice can be explained by the constitutive expression of the FasL in lpr-derived T cells.

Immunofluorescence techniques for the identification of immune effector cells in rat heart: applications to the study of the myocarditis induced by interleukin-2

A detailed description is presented of immunohistochemical methods for identification of various types of immune effector cells in rat heart, involving the use of antibodies conjugated with different fluorochromes for the simultaneous demonstration of 2 or 3 different antigens by means of fluorescence microscopy. The initial results of the application of these techniques to the study of the myocarditis induced by interleukin-2 (IL-2) are also presented. Antibodies used included: OX6 antibody (for MHC class II molecules, mainly expressed by dendritic cells): W3/25 and OX8 antibody, for the demonstration of the rat equivalents of CD5 and CD8, respectively: asialo-GM1 ganglioside antibody for the identification of natural killer (NK) cells and lymphokine activated killer (LAK) cells, and ED2 antibody for labeling of macrophages. Fluorochromes used were: fluorescein isothiocyanate (green), tetramethylrhodamine isothiocyanate (red), Texas red sulfonyl chloride (red), and 7-amino-4-methylcoumarin-3-acetic acid (blue). IL-2-induced myocarditis was characterized histologically by infiltration of the myocardium by mononuclear inflammatory cells, microvascular alteration, interstitial edema, and myocyte damage and necrosis. In the initial stages, NK/LAK cells were the predominant type of infiltrating lymphocytes; however, the numbers of these cells decreased sharply in subsequent stages. Macrophages also were initially abundant, and continued to be prevalent throughout the late stages. CD8+ lymphocytes were more numerous than CD4+ lymphocytes. Dendritic-cells showed a diffuse increase in number and also accumulated around foci of myocyte necrosis. Three phenotypes of dendritic cells were recognized, and the possible implications of these findings are discussed. It is hoped that these techniques will prove useful for the immunohistochemical evaluation of various inflammatory diseases of the heart.

Detection of kappa-opioid receptor mRNA in immature T cells

The R1.1 cell line has been shown to express kappa-opioid receptors on the cell surface. Our analysis shows that the R1.1 cell line exhibits a CD4NEG CD8NEG CD3LOW CD25LOW cell surface phenotype, characteristic of thymocytes in one of the early stages of differentiation. We have developed reverse transcriptase polymerase chain reaction (RT-PCR) conditions that permit the detection of mRNA coding for the kappa-receptor. Using cell fractionation techniques we have isolated CD4NEG CD8NEG thymocytes, and analysis by RT-PCR shows that these primary immature thymocytes also express the kappa-opioid receptor. We hypothesize that the expression of kappa-opioid receptor may be a marker which is characteristic of immature T development.