CD4+ T-cell responses to Epstein-Barr virus (EBV) latent-cycle antigens and the recognition of EBV-transformed lymphoblastoid cell lines

There is considerable interest in the potential of Epstein-Barr virus (EBV) latent antigen-specific CD4+ T cells to act as direct effectors controlling EBV-induced B lymphoproliferations. Such activity would require direct CD4+ T-cell recognition of latently infected cells through epitopes derived from endogenously expressed viral proteins and presented on the target cell surface in association with HLA class II molecules. It is therefore important to know how often these conditions are met. Here we provide CD4+ epitope maps for four EBV nuclear antigens, EBNA1, -2, -3A, and -3C, and establish CD4+ T-cell clones against 12 representative epitopes. For each epitope we identify the relevant HLA class II restricting allele and determine the efficiency with which epitope-specific effectors recognize the autologous EBV-transformed B-lymphoblastoid cell line (LCL). The level of recognition measured by gamma interferon release was consistent among clones to the same epitope but varied between epitopes, with values ranging from 0 to 35% of the maximum seen against the epitope peptide-loaded LCL. These epitope-specific differences, also apparent in short-term cytotoxicity and longer-term outgrowth assays on LCL targets, did not relate to the identity of the source antigen and could not be explained by the different functional avidities of the CD4+ clones; rather, they appeared to reflect different levels of epitope display at the LCL surface. Thus, while CD4+ T-cell responses are detectable against many epitopes in EBV latent proteins, only a minority of these responses are likely to have therapeutic potential as effectors directly recognizing latently infected target cells.

Asymptomatic deficiency in the peptide transporter associated to antigen processing (TAP)

Human HLA class I deficiency is a rare disease which, in most of the patients described to date, results from a defect in subunit 1 or 2 of the peptide transporter associated with antigen processing (TAP). The clinical features of TAP deficiency include a chronic inflammation of the respiratory tract and/or granulomatous skin lesions. In this report, we describe two adult siblings with an HLA class I deficiency. One individual had only spontaneously-healing skin granulomatous lesions, while the second did not display any of the symptoms associated with HLA class I deficiency and could be considered to be healthy. We show that the patients display a homozygous TAP2 mutation which blocks the maturation of HLA class I molecules. Cell surface expression of these molecules is strongly reduced, but three times higher than on cells from other previously described TAP-deficient individuals. This higher expression results, at least in part, from the presence of HLA-B7 molecules which are probably empty of peptide. The numbers of CD8+ alphabeta T cells are almost normal in these patients. The anti-EBV T-cell response of one patient is mediated by HLA-B7 restricted CD8+ alphabeta T lymphocytes recognizing the BMRF1 nuclear EBV antigen, demonstrating that CD8+ alphabeta T cells can participate in anti-viral responses. This study shows that TAP deficiency can remain totally asymptomatic for several decades, and suggests that in some cases, TAP-independent immune responses provide efficient protection from most of the common intracellular pathogens.

Immunodominant CD8 T cell response to Epstein-Barr virus

Epstein-Barr virus (EBV) provides one of the most informative systems for analysing cytotoxic T lymphocyte responses in humans. The viral infection and its persistence are the results of an alternation of lytic and latent phases that are controlled by the immune response. Using a transient COS transfection assay that permits semi-quantitative estimation of CD8 T cell responses against a large number of HLA/viral protein combinations, we analyzed responses to EBV within a large number of polyclonal T cell lines. This allowed a rapid identification of major epitopes and the demonstration that EBV-specificT cells were mainly directed against a restricted set of immunodominant epitopes, primarily generated during the early lytic cycle. Knowledge of the antigen specificity of CDB T cell responses against EBV should help generate cytotoxic T cell lines to this herpesvirus, and more generally to study the molecular basis of immunodominance.

Frequent recognition of BCRF1, a late lytic cycle protein of Epstein-Barr virus, in the HLA-B*2705 context: evidence for a TAP-independent processing

Using a transient COS transfection assay, allowing a rapid estimation of the dominant CD8(+) T cell responses against a large number of HLA/viral protein combinations within polyclonal cell lines, we searched for HLA-B*2705-restricted CD8 T cell responses to Epstein-Barr virus (EBV) within T cell samples enriched for EBV-reactive cells. Among the 18 EBV proteins tested, only 2, the latent protein EBNA3A and the late lytic protein BCRF1 (viral IL-10), appeared dominant in the B27 context, as they triggered significant TNF and cytolytic responses in some donors. We provide evidence that the B27/BCRF1 epitope (RRLVVTLQC) is located in the signal sequence and that it can be presented in a TAP-independent manner. Using B27/BCRF1 monomeric complexes coated on immunomagnetic beads, we sorted out BCRF1-specific CD8 T cells from 8 of 15 HLA-B27(+) donors. This is, to our knowledge, the first demonstration of a recognition of BCRF1, suggesting that some immune control against EBV exists even during the late stage of the lytic cycle. This result also strengthens the unusual ability of HLA-B*2705 to present peptide in a TAP-independent manner.

Regulation of inhibitory and activating killer-cell Ig-like receptor expression occurs in T cells after termination of TCR rearrangements

A small fraction of T cells expresses killer-cell Ig-like receptors (KIR), a family of MHC class I-specific receptors that can modulate TCR-dependent activation of effector functions. Although KIR(+) cells are enriched within Ag-experienced T cell subsets, the precise relationships between KIR(+) and KIR(-) T cells and the stage of KIR induction on these lymphocytes remain unclear. In this study, we compared KIR(-) and KIR(+) alphabeta T cell clones, sorted by means of the CD158b (KIR2DL2/KIR2DL3/KIR2DS2) specific mAb GL183. We isolated several pairs of CD158b(+) and CD158b(-) alphabeta T cell clones sharing identical productive and nonproductive TCR transcripts. We showed that expression of functional KIR on T cells is regulated after termination of TCR rearrangements. Transcriptional regulation of KIR genes was documented in multiple T cell clones generated from the same donor, and the presence of KIR transcripts was also detected in KIR(-) T cells. These results document a complex regulation of KIR expression in T cells at both pre and posttranscriptional levels, under the control of yet undefined signals provided in vivo.

A global appraisal of immunodominant CD8 T cell responses to Epstein-Barr virus and cytomegalovirus by bulk screening

Knowledge of the immunodominant responses to Epstein-Barr Virus (EBV) and human cytomegalovirus (HCMV) should help to generate cytotoxic T cell lines to these herpesviruses. Here we report on the analysis of CD8 T cell responses to EBV and HCMV in the blood of kidney transplant recipients undergoing viral reactivation (n = 16) and in healthy virus carriers (n = 10). We used a transient COS transfection assay that permits semi-quantitative estimation of CD8+ T cell responses against a larger number of HLA/viral protein combinations within polyclonal T cell lines and thus allows a rapid identification of major epitopes. From the comparison of these responses to those that we previously described in the synovial fluid of patients suffering from various forms of chronic arthritis (n = 32), it appears that EBV-specific T cells are mainly directed against a restricted set of immunodominant epitopes, primarily generated during the early lytic cycle and that both IE1 and pp65 are targets of the anti-HCMV response. We suggest that this method could be generally applied to the rapid identification of immunodominant T cell epitopes in viral and tumor immunity, and could help selecting HLA-peptide complexes that could be used to detect and sort specific T cell populations.

The T cell repertoire selected in vitro against EBV: diversity, specificity, and improved purification through early IL-2 receptor alpha-chain (CD25)-positive selection

Polyclonal T cell lines specific for EBV proteins have proved efficient in preventing EBV-related immunoblastic lymphoma after allogeneic bone marrow transplantation. To gain insight into the composition of the EBV-specific T cell repertoire that ensured patient protection, we performed for the first time an extensive characterization of eight cytotoxic T cell lines selected in vitro against EBV-transformed autologous lymphoblastoid cell lines (BLCL). These T cell lines consist of 50-100 distinct T cell clones, of which 32-96% are specific for autologous BLCL. Moreover, we demonstrate that reactivities against only five EBV proteins (BZLF1, BMLF1, EBNA-3A, EBNA-3C, and LMP2) cover 86% (32/37) of the specificities detected. In addition, we describe an improved method of T cell harvesting using a CD25 selection procedure which reduces the time required to obtain specific T cells and improves the purity of EBV-specific T cells, thus showing promise for use in adoptive transfer protocols.

EBV gene expression not altered in rheumatoid synovia despite the presence of EBV antigen-specific T cell clones

T cells infiltrating the rheumatoid arthritis (RA) joint are oligoclonal, implicating an Ag-driven process, but the putative joint-specific Ags remain elusive. Here we examine expression of selected EBV genes in RA synovia and find no abnormal expression in RA. DNA of CMV and EBV was detectable by PCR in the synovial tissue of RA. RNA of several latent and lytic EBV genes was also detectable. However, there were no differences in EBV gene expression in synovial tissues or peripheral blood when comparing RA with osteoarthritis, Gulf War syndrome, and other disease controls. RA synovia with highly expanded CD8 T cell clones reactive with defined EBV peptide Ags presented by HLA class I alleles lacked evidence of abnormal mRNA expression for the relevant EBV Ag (BZLF1) or lacked amplifiable mRNA (BMLF1). Thus, local production of EBV Ags in synovial tissues may not be the cause of the accumulation of T cell clones specific for these Ags. Instead, APCs loaded with processed EBV peptides may migrate to the synovium. Alternatively, EBV-specific T cells clones may be generated in other tissues and then migrate to synovia, perhaps due to cross-reactive joint-specific Ags or because of expression of homing receptors.

Frequent enrichment for CD8 T cells reactive against common herpes viruses in chronic inflammatory lesions: towards a reassessment of the physiopathological significance of T cell clonal expansions found in autoimmune inflammatory processes

We recently evidenced a dramatic enrichment for T cells reactive against Epstein-Barr virus (EBV) within inflamed joints of two rheumatoid arthritis patients. To assess the generality of this phenomenon and its relevance to autoimmunity, we studied the responses of CD8 T cells from patients with either acute or chronic inflammatory diseases (rheumatoid arthritis: n = 18, ankylosing spondylitis: n = 5, psoriatic arthritis: n = 4, Reiter's syndrome: n = 3, arthrosis: n = 2, uveitis: n = 2, multiple sclerosis: n = 2, encephalitis: n = 1) against viral proteins derived from EBV and another common herpes virus, human cytomegalovirus (CMV). T cell responses against EBV and/or CMV epitopes were frequently observed within CD8 T cells derived from chronic inflammatory lesions, irrespective of their location (knee, eye, brain) and autoimmune features. In most cases, CD8 T cells derived from affected organs yielded stronger anti-viral T cell responses than CD8 T cells derived from patients' PBL, even in chronic inflammatory diseases devoid of autoimmune features or induced by defined bacterial agents. Taken together, these results suggest that the presence of virus-specific T cells within inflamed lesions of patients suffering from autoimmune diseases is a general phenomenon associated with chronic inflammation rather than the initiating cause of the autoimmune process. Since this phenomenon was sometimes associated with long-term T repertoire biases within inflamed lesions, the physiopathological significance of T cell clonal expansions found in a recurrent fashion within chronically inflamed autoimmune lesions should be interpreted with caution.

Exon III splicing switch of fibroblast growth factor (FGF) receptor-2 and -3 can be induced by FGF-1 or FGF-2

An essential feature of fibroblast growth factor receptors (FGFRs) is the existence of multiple possibilities of alternative splicing. One of these concerns sequences of the mRNA coding for the C-terminal half of Ig domain 3 which corresponds to a part of the ligand-binding site: two alternative exons, IIIb and IIIc, encode the C-terminal half of Ig domain 3. The IIIb/IIIc choice in the FGFR-2 and FGFR-3 is strictly tissue-specific, the IIIb exon being expressed exclusively in epithelial cells. We describe here a reversible switch from IIIb to IIIc for FGFR-2 and FGFR-3 under the influence of exogenous and endogenous FGF-1 or FGF-2. We observed that FGF-induced FGF receptor exon switching (i) occurred as early as 1 h after exposure to FGF (ii) was receptor-mediated (iii) was dependent on cell confluency and showed a link with the cell cycle (iv) was correlated with a reversible loss of epithelial properties. These results support a role for FGF in the regulation of expression of alternatively spliced FGFR mRNA.

Human peptide transporter deficiency: importance of HLA-B in the presentation of TAP-independent EBV antigens

Two siblings with a peptide TAP deficiency were recently described. Despite poor cell surface expression of HLA class I molecules, these patients were not unusually susceptible to viral infections. The majority of the cell surface-expressed class I molecules were HLA-B products as assessed by cytofluorometry and biochemical analysis. Analysis of two peptides eluted from the class I molecules expressed by TAP-deficient EBV B lymphoblastoid cell lines indicated that both were derived from cytosolic proteins and presented by HLA-B molecules. Peripheral alphabeta CD8+ T cells were present and their TCR repertoire was polyclonal. Most of the alphabeta CD8+ T cell clones studied (21 of 22) were nonreactive against cells expressing normal levels of the same HLA alleles as those of the TAP-deficient patients. However, it was possible to isolate one cytotoxic CD8+ alphabeta T cell clone recognizing the EBV protein LMP2 presented by HLA-B molecules on TAP-deficient cells. These observations suggest that in the TAP-deficient patients, CD8+ alphabeta T cells could mature and be recruited in immune responses to mediate HLA class I-restricted cytotoxic defense against viral infections. They also strengthen the physiologic importance of a TAP-independent processing pathway of the LMP2 protein, which was previously shown to contain several other TAP-independent epitopes.

Human peptide transporter deficiency: importance of HLA-B in the presentation of TAP-independent EBV antigens

Two siblings with a peptide TAP deficiency were recently described. Despite poor cell surface expression of HLA class I molecules, these patients were not unusually susceptible to viral infections. The majority of the cell surface-expressed class I molecules were HLA-B products as assessed by cytofluorometry and biochemical analysis. Analysis of two peptides eluted from the class I molecules expressed by TAP-deficient EBV B lymphoblastoid cell lines indicated that both were derived from cytosolic proteins and presented by HLA-B molecules. Peripheral alphabeta CD8+ T cells were present and their TCR repertoire was polyclonal. Most of the alphabeta CD8+ T cell clones studied (21 of 22) were nonreactive against cells expressing normal levels of the same HLA alleles as those of the TAP-deficient patients. However, it was possible to isolate one cytotoxic CD8+ alphabeta T cell clone recognizing the EBV protein LMP2 presented by HLA-B molecules on TAP-deficient cells. These observations suggest that in the TAP-deficient patients, CD8+ alphabeta T cells could mature and be recruited in immune responses to mediate HLA class I-restricted cytotoxic defense against viral infections. They also strengthen the physiologic importance of a TAP-independent processing pathway of the LMP2 protein, which was previously shown to contain several other TAP-independent epitopes.

Identification of a gp100 epitope recognized by HLA-A3 restricted melanoma infiltrating lymphocytes

The large majority of known melanoma-associated antigenic peptides presented by MHC class I molecules are presented by the most frequent allele, HLA-A*0201. Thus although a significant percentage of Caucasians express HLA-A3, no melanoma-associated antigenic peptide presented by this allele has yet been identified. We show here that the T cell clone M45-10 isolated from tumor infiltrating lymphocytes recovered from a melanoma biopsy recognizes the gp100-derived peptide ALLAVGATK presented by HLA-A*0301. Since gp100 is expressed on most melanoma cells, our results imply that the gp100-based anti-melanoma strategies developed for individuals expressing HLA-A2 will also be applicable to those expressing HLA-AS (about one Caucasian in four). gp100 is therefore a particularly promising melanoma antigen, as different peptides derived from it can be presented by at least two different frequently encountered HLA class I molecules.

Overexpression of vascular endothelial growth factor induces cell transformation in cooperation with fibroblast growth factor 2

Vascular endothelial growth factor (VEGF) is a family of homodimeric proteins produced from a single gene by alternative splicing of the VEGF transcript. VEGF induces in vivo angiogenesis and vascular permeability. We have recently demonstrated that VEGF is an autocrine growth factor for retinal pigment epithelial (RPE) cells. To further understand the role of VEGF, we overexpressed VEGF in rat RPE cells. The transfected cells exhibited a growth advantage in vitro and an increased response to the mitogenic effect of fibroblasts growth factor-2 (FGF-2), and formed colonies in soft agar upon FGF-2 addition. Moreover, analysis of FGF-receptors evidenced a dramatic increase in FGFR-1 mRNA and protein level, supporting the hypothesis that this receptor mediates the transforming effect of FGF-2. These results reveal that the oncogenic role of VEGF is exerted through a cross regulation between VEGF and FGF signal transduction pathways.

T cell response to Epstein-Barr virus transactivators in chronic rheumatoid arthritis

Rheumatoid arthritis is a multistep disorder associated with autoimmune features of yet unknown etiology. Implication of viruses such as Epstein-Barr virus (EBV) in rheumatoid arthritis pathogenesis has been suspected on the basis of several indirect observations, but thus far, a direct link between EBV and rheumatoid arthritis has not been provided. Here we show that a large fraction of T cells infiltrating affected joints from a patient with chronic rheumatoid arthritis recognizes two EBV transactivators (BZLF1 and BMLF1) in a major histocompatibility complex-restricted fashion. Responses to these EBV antigens by synovial lymphocytes from several other chronic rheumatoid arthritis patients were readily detectable. Thus these results suggest a direct contribution of EBV to chronic rheumatoid arthritis pathogenesis. They also demonstrate for the first time the occurrence of T cell responses against EBV transactivating factors, which might be central in the control of virus reactivation.

The choice between alternative IIIb and IIIc exons of the FGFR-3 gene is not strictly tissue-specific

An essential feature of fibroblast growth factor receptors (FGFR) is the existence of multiple possibilities for alternative splicing. One of these concerns sequences of the mRNA coding for the C-terminal half of Ig domain 3 which corresponds to a part of the ligand-binding site. Two alternative exons, IIIb and IIIc, encode the C-terminal half of Ig domain 3. We show here that the alternative splicing choice between IIIb and IIIc exons of the FGFR-3 is not strictly tissue-specific: epithelial cells show exclusively IIIb transcripts while fibroblastic cells show a mixture of IIIb and IIIc transcripts. This is in contrast with the strictly exclusive alternative choice between IIIb or IIIc exons of the FGFR-2 gene: epithelial cells make only the IIIb choice while fibroblastic cells make only the IIIc choice.

Oncoprotein fos activation in epithelial-cells induces an epitheliomesenchymal conversion and changes the receptor encoded by the fgfr-2 messenger-RNA from k-sam to bek

Activation of c-Fos, by using an inducible c-Fos estrogen receptor fusion protein, triggers the epitheliofibroblastoid cell conversion of mouse mammary epithelial cells. We show that this change in phenotype is accompanied by a definitive switch of the fibroblast growth factor receptor 2 from K-SAM to BEK. This splicing switch occurs a few hours after estrogen stimulation. Our data suggest that Fos proteins could be important in modulating the FGFR-2 splicing choice. Moreover, these observations reinforce previous evidence that the BEK/K-SAM choice is strictly tissue-specific: the K-SAM exon is expressed exclusively in epithelial cells, the BEK exon in cells of the fibroblastic type.

Early separation of B and T lymphocyte precursors in chick embryo

Embryonic chimeras were used to demonstrate an early separation of chicken T and B cell precursors. Genetically polymorphic cell surface antigens, Bu-1 and Ov, which are expressed on cells of the B and T lineage, respectively, are useful markers in adoptive cell transfer studies. Allelic products Bu-1a and Bu-1b can be detected with monoclonal antibodies (mAbs) L22 and 11G2, respectively, and the Ov antigen with mAb 11A9. Chimeric chickens were constructed by reconstituting irradiated 14-d Ov- H.B19 embryos with the sorted Bu-1+ or Bu-1- fractions of spleen cells from age-matched H.B19 Ov+ embryos. Chimeras were analyzed, 3-4 wk after hatching, for the presence of Ov+ cells in the bursa, thymus, spleen, and peripheral blood lymphocytes. T cell precursors giving rise to thymocytes and peripheral T cells were present only in the Bu-1-, but not in the Bu-1+, fraction. We previously demonstrated that, in contrast, all B cell precursors in spleen from 14-d embryos are exclusively present in the Bu-1+ fraction. We also analyzed the immunoglobulin light chain gene rearrangement in these populations by polymerase chain reaction. We show here that VJ recombination occurs in the Bu-1+, but not in the Bu-1-, fraction of spleen. These data demonstrate an early commitment to the B cell lineage, which occurs before the colonization of the bursa of Fabricius. Segregation of B cell precursors from the other hemopoietic precursors, and consequently separation of T and B cell precursors, occurs before the colonization of the primary lymphoid organs.

Multiple mRNAs code for proteins related to the BEK fibroblast growth factor receptor

The BEK transmembrane protein tyrosine kinase is a receptor for both acidic and basic fibroblast growth factors. We identify several different transcripts which code for BEK-related proteins. These proteins differ from BEK in regions expected to control receptor activity. Thus, some of the proteins have altered extracellular, ligand-binding domains, and others an altered carboxy-terminal tail. Still other forms of BEK differ only in their juxtamembrane domains. Sequencing of parts of the BEK gene shows that alternative splicing of the premessenger can account for at least some of this diversity. In particular, an apparently tissue specific, mutually exclusive splicing of two internal exons permits both the previously described K-SAM mRNA and the BEK mRNA to be derived from the same premessenger.

Assignment by in situ hybridization of a fibroblast growth factor receptor gene to human chromosome band 10q26

A 2.3-kb cDNA probe for the human bek fibroblast growth factor receptor was used to determine the chromosomal localization of the corresponding gene by in situ hybridization. The results show that this gene, a form of which is amplified in some poorly differentiated stomach cancers, is localized on chromosome region 10q26. The two previously identified fibroblast growth factor receptor genes are thus not on the same chromosome, as the related flg ("fms-like gene") fibroblast growth factor receptor gene has previously been mapped to human chromosome region 8p12.

Monoclonal autoantibodies from insulin-dependent diabetic patients: autoantibodies against beta-cell surface or cytoplasmic antigens

To investigate the target antigen(s) recognized during the autoimmune process in insulin-dependent diabetes mellitus (IDDM), we produced human monoclonal antibodies by Epstein-Barr virus transformation of peripheral blood lymphocytes from a large number (n = 50) of newly diagnosed IDDM patients. Screening by indirect immunofluorescence assay, using the RINm5F rat insulinoma cell line and eight other human or rat tumour cell lines, was performed to identify monoclonal antibodies that reacted with either membrane or cytoplasmic antigens. Eighteen IgM monoclonal antibodies reacting with cytoplasmic antigens of RIN cells were obtained; 14 of them also showed a staining of the cytoplasm of various non-beta-cell lines, while four displayed a binding restricted to beta-cells among the panel tested. However, among three monoclonal antibodies reacting with the membrane of RIN cells, one (HMD-1) produced an IgG antibody with a binding restricted to the membrane of beta-cells (RIN, HIT, and normal rat islet cells). The membrane antigens of HMD-1 were identified in Western blotting as proteins with molecular weights of 64 and 70 kD. This antibody had no apparent cytotoxic effect on RIN cells. These data suggest that, apart from 'natural autoantibodies,' it is feasible to obtain human monoclonal antibodies from IDDM patients that bind specifically to the beta-cell cytoplasm or to the beta-cell membrane.

The role of thymic epithelium in the acquisition of tolerance

There are two separate mechanisms of induction of T-cell tolerance in the thymus. First, MHC molecules expressed on bone-marrow-derived cells can cause clonal deletion of autoreactive cells. Second, as discussed here by Elisabeth Houssaint and Martin Flajnik, thymic epithelial cells can generate a form of tolerance that does not eliminate self-reactive clones. This nondeletional mechanism, which is also a feature of the other MHC class-II-bearing epithelia, may contribute to the establishment of tolerance-maintaining regulatory networks.

Related fibroblast growth factor receptor genes exist in the human genome

We have isolated, from a human tumor cDNA library, a gene encoding a putative receptor-like protein-tyrosine kinase that we call TK14. The amino acid sequence of the TK14 protein is closely related to the available partial sequence of the mouse protein bek, and more distantly related to the sequences of a chicken basic fibroblast growth factor receptor (73% sequence homology) and the apparent human equivalent of this receptor, the FLG protein (encoded by the fms-like tyrosine kinase gene). Overexpression of the TK14 protein by transfection of COS-1 cells with the corresponding cDNA in a simian virus 40-based expression vector leads to the appearance of new cell-surface binding sites for both acidic and basic fibroblast growth factors. This has been demonstrated by specific binding assays and chemical cross-linking experiments using 125I-labeled growth factors. It appears, therefore, that the human genome contains at least two distinct genes, for TK14 and FLG, that code for related fibroblast growth factor receptors.

Tissue distribution and appearance in ontogeny of alpha/beta T cell receptor (TCR2) in chicken

We have performed immunoperoxidase staining on cryostat tissue sections and immunofluorescence analysis on cell suspensions to identify cells expressing the alpha/beta T cell antigen receptor during ontogeny and adult life in chickens. We used the mouse monoclonal antibody, TCR2, which was previously shown to recognize the alpha/beta TCR in chickens. TCR2+ cells were observed in thymic cortex and medulla and in T-dependent areas of spleen, intestine, and cecal tonsils of young adult chickens. Some TCR2+ cells were found in the cortex of bursal follicles and in liver. The first TCR2+ cells appear in thymus on Day 13 of the embryonic life and it is only after hatching that TCR2+ cells begin to migrate to the periphery.

Class II MHC antigen induction on rat insulinoma (RINm5F) and colon carcinoma (TS) cells by co-culture with diabetic and normal xenogenic lymphocytes

Two MHC Class II-negative rat epithelial cell lines (RINm5F beta-cells and TS colic cells) were co-cultured with xenogenic lymphocytes from Type I diabetic patients or from low-dose streptozotocin (SZ) diabetic mice. MHC Class II antigens (Ag) were easily induced on both cell lines in such co-culture conditions, representing an experimental approach to insulitis. Our data indicate that: (1) lymphocytes from diabetic patients or from SZ mice were more efficient than lymphocytes from healthy controls in inducing Class II Ag on RIN cells. Lymphocytes from patients with autoimmune thyroid diseases were also more efficient than control lymphocytes, indicating that the ability to induce Class II may be related to the activation of lymphocytes rather than being diabetes-specific. (2) Rat colon carcinoma cells (TS) were also induced to express high levels of Class II Ag upon co-culture with SZ or control mouse lymphocytes. (3) Class II+ RIN cells were observed after 24 h of co-culture; their number increased after 48 and 72 h. The number of class II+ RIN increased proportionally to the number of lymphocytes in the culture. (4) Induction of Class II Ag was obtained by cell-free supernatants of mouse lymphocytes/RIN co-cultures and was inhibited by cyclosporine A, suggesting that Class II induction in this model is mediated by lymphokines. (5) Depletion experiments indicate that both monocytes and lymphocytes play a role in this Class II induction.

In vitro relationship of CD4 cells from type I diabetic patients and xenogeneic beta-cell membranes

In a rosette assay, 63 patients with recent-onset type I (insulin-dependent) diabetes mellitus had a higher (P less than .001) number of lymphocytes adhering to rat insulinoma RINm5F cells (diabetic rosettes) than 153 healthy control (background rosettes) or 20 nondiabetic subjects with other organ-specific autoimmune diseases. Furthermore, lymphocytes from diabetic patients displayed a highly correlated (r = .97, P less than .001) binding on two different xenogeneic beta-cell lines (RIN and hamster insulinoma HIT cells). This phenomenon was not found on a panel of seven non-beta-cell lines (e.g., exocrine pancreatic cells, endocrine cells). By increasing lymphocyte-to-RIN ratios (0.25:1 to 30:1), the supernumerary RIN-adherent lymphocytes from diabetic patients, expressed as the percentage of lymphocytes involved conjugates, were only detectable at lower ratios (0.25:1 to 4:1), and their binding efficiency was two times higher than that of control lymphocytes. This efficiency fell at higher ratios (greater than 4:1) to the level of background rosettes that remained constant through the ratio scale. This specific RIN-rosette formation was abrogated when lymphocytes from diabetic patients were preabsorbed on beta-cells (either HIT or RIN) but not on non-beta-cells, whereas preabsorption of control lymphocytes did not modify the number of background rosettes. In addition, diabetic rosettes, but not background rosettes, were inhibited by competition with RIN membrane extracts but not by non-beta-cell extracts. Moreover, diabetic rosettes were inhibited during blocking experiments with anti-CD3 monoclonal antibody (MoAb) but not with unrelated MoAbs.(ABSTRACT TRUNCATED AT 250 WORDS)

Bu-1 antigen expression as a marker for B cell precursors in chicken embryos

Genetically polymorphic cell surface antigen, Bu-1, is expressed on B cells as well as on a subset of macrophages. Bu-1+ cells are also present in embryonic spleen and bone marrow, and these could represent prebursal precursors for B cells and Bu-1+ macrophages. To test the repopulation capacity of these cells we sorted 14-day embryonic spleen cells from Bu-1a-homozygous donors into Bu-1a+ and Bu-1a- fractions and transferred them into age-matched irradiated Bu-1b-homozygous recipients. Four to six weeks after hatching, the recipients were analyzed for Bu-1 chimerism. The results demonstrate that B cell precursors are exclusively present in the Bu-1+ population of 14-day embryonic spleen, whereas the Bu-1+ macrophage subpopulation can be repopulated by either the Bu-1+ or the Bu-1- fraction of these embryonic cells. Bone marrow cells from young chickens could also repopulate the Bu-1+ macrophage subset but not the B cell compartment, thus confirming previous data that postnatal bone marrow does not contain B cell precursors. These results demonstrate that all B cell precursors in the 14-day embryonic spleen carry the Bu-1 antigen, and suggest that there is no lineage relationship between the Bu-1+ cells and macrophages.

B cell precursors in chick embryos surgically bursectomized at 72 h of incubation

To determine the presence of precursor B cells in chick embryos surgically bursectomized at 72 h of incubation (E-Bx) we studied chick chimeras that were produced by establishing parabiotic connections between blood vessels of chorioallantoic membranes of normal and surgically bursectomized chick embryos. Using sex chromosomes and a B cell alloantigen (Bu-1a) as markers we showed that chick embryos bursectomized at 72 h of incubation contain B cell precursors capable of colonizing the bursa of Fabricius and developing into B lymphocytes. The repopulation capacity of 14-day-old embryonic spleen cells from E-Bx recipients was tested by transferring them into age-matched X-irradiated Bu-1-disparate embryos. The results show that B cell precursors are present in 14-day spleen of chick embryos bursectomized at 72 h of incubation. These precursors carry the Bu-1 B cell alloantigen, suggesting that commitment to the B cell lineage can take place in the absence of bursa.

Inability of adult circulating haemopoietic stem cells to sustain haemopoiesis in mouse fetal liver microenvironment

Liver rudiments were removed from mouse embryos at Day 9 of gestation, before the 28-somite stage, when they are still not colonized by extrinsic haemopoietic stem cells (HSC), and they were grafted under the kidney capsule of syngeneic adult mice. Hepatocytes differentiated normally, but no colonization by HSC occurred. As control, we used precolonized thymic rudiments taken at Day 10 of gestation, when they are still included in the third branchial arches. They were grafted in the same conditions as liver rudiments and they became colonized by extrinsic HSC that gave rise to lymphocytes. So, adult HSC are not able to colonize the fetal liver rudiment while they have the capacity to home the fetal thymus. We discuss these results in terms of an ontogenic maturation of HSC that could change their homing capacities around birth.

Cytoadherence of lymphocytes from type I diabetic subjects to insulin-secreting cells. Marker of anti-beta-cell cellular immunity

We studied the ability of lymphocytes from type I (insulin-dependent) diabetic patients to adhere to murine beta-cells. Lymphocytes from 17 recent-onset type I diabetic subjects (less than 6 mo) displayed enhanced ability to form rosettes with RINm5F cells (P less than .001) compared with lymphocytes from 27 healthy subjects forming background rosettes, whereas the number of RIN cytoadherent lymphocytes was unimpaired in 12 type II (non-insulin-dependent) diabetic subjects. This phenomenon tended to decline in 21 subjects with long-standing diabetes (greater than 1 yr) who taken as a group presented a normal number of RIN rosetting lymphocytes. The islet specificity of these diabetic rosettes was confirmed because, compared with controls, lymphocytes from recent-onset type I diabetic subjects also displayed a greater intensity of adherence to normal mouse islets but not to unrelated K562 and TS cell lines. As demonstrated by indirect immunofluorescence studies, these diabetic rosettes contained 54% of T-lymphocytes (OKT3+, OKT4+, or OKT8+), whereas only 20% of T-lymphocytes were found in background rosettes. The high percentage (66%) of la+ cells found in diabetic rosettes suggests that at least some of the cytoadherent T-lymphocytes from recent-onset type I diabetic subjects are activated. Natural killer (NK) cells do not seem to be the major cell type implicated in this phenomenon, because Leu 11+ cells were less represented in diabetic rosettes (25%) than in background rosettes (53%).(ABSTRACT TRUNCATED AT 250 WORDS)

Ontogeny and tissue distribution of the chicken Bu-1a antigen

By using a sensitive technique of immunofluorescence on polyethylene glycol-embedded tissue sections, we could better determine the distribution of L22+ cells in embryonic and adult chickens. L22 mAb was originally described as reacting with bursa and bursa-derived lymphocytes. We now present evidence to suggest that this mAb also reacts with a subset of macrophages found in bursa, thymus, spleen, liver, intestine and peritoneum. The L22+ cells appear early during embryonic life, simultaneously in yolk sac, bursa, thymus, spleen and bone marrow. At all steps of their ontogeny, thymocytes were L22-, while most, if not all, bursal lymphoid cells were L22+. Moreover, L22 antigen can be detected on haemopoietic cells probably precursors, before and during their entry into the bursal rudiment on Day 9 or 10 of embryonic life. We conclude from these data that L22 is not restricted to the B-cell lineage as it is shared with a subset of macrophages. Furthermore, our observations of L22+ cells during embryonic life favour the hypothesis of separate lineages for B-cell and T-cell precursors in chick embryo, which was previously put forward on the basis of different sets of experiments.

Cell lineage segregation during bursa of Fabricius ontogeny

The population dynamics of myeloid and lymphoid lineages during bursa of Fabricius ontogeny were analyzed by immunofluorescence by using two monoclonal antibodies (mAb). CL-1 mAb reacts with all chicken hemopoietic cells, except mature erythrocytes. L22 mAb reacts with bursa and bursa-derived lymphocytes, with a minor subset of macrophages and with some cells of the thymic medulla. The staining of embryonic bursas by these antibodies helps to distinguish between two different lineages of hemopoietic cells: CL-1+/L22+ cells represent B lymphocytes and a minor subset of macrophages, while CL-1+/L22- cells correspond to most of the macrophages and to the granulocytes, which disappear at the end of the embryonic life. CL-1+/L22- as well as CL-1+/L22+ cells were first observed outside the bursal rudiment. This indicates that there is a pre-bursal segregation between these two hemopoietic lineages and that two different kinds of precursors colonize the bursal rudiment at about the same time (day 9 for CL-1+/L22- cells and days 9 or 10 for CL-1+/L22+ cells). Moreover our data show that the colonization of the bursal epithelium by hemopoietic precursors is a two-step phenomenon. The first cells which enter belong to the CL-1+/L22- lineage, express Ia-like antigens at a high level, are dendritic in morphology, and represent cells of the macrophage/dendritic cell lineage. They are responsible for the formation of the epithelial bud which are then colonized by a small number of lymphoid precursors which belong to the CL-1+/L22+ lineage. Quail-chick bursa grafting experiments were also performed and the grafts were examined for CL-1 (restricted to chicken hemopoietic cells) and L22 reactivity. These observations confirmed our previous findings about the kinetics of the colonization of bursal rudiment by hemopoietic precursors and give support for a pre-bursal segregation between two hemopoietic pathways.

Cell lineage segregation during bursa of Fabricius ontogeny

The population dynamics of myeloid and lymphoid lineages during bursa of Fabricius ontogeny were analyzed by immunofluorescence by using two monoclonal antibodies (mAb). CL-1 mAb reacts with all chicken hemopoietic cells, except mature erythrocytes. L22 mAb reacts with bursa and bursa-derived lymphocytes, with a minor subset of macrophages and with some cells of the thymic medulla. The staining of embryonic bursas by these antibodies helps to distinguish between two different lineages of hemopoietic cells: CL-1+/L22+ cells represent B lymphocytes and a minor subset of macrophages, while CL-1+/L22- cells correspond to most of the macrophages and to the granulocytes, which disappear at the end of the embryonic life. CL-1+/L22- as well as CL-1+/L22+ cells were first observed outside the bursal rudiment. This indicates that there is a pre-bursal segregation between these two hemopoietic lineages and that two different kinds of precursors colonize the bursal rudiment at about the same time (day 9 for CL-1+/L22- cells and days 9 or 10 for CL-1+/L22+ cells). Moreover our data show that the colonization of the bursal epithelium by hemopoietic precursors is a two-step phenomenon. The first cells which enter belong to the CL-1+/L22- lineage, express Ia-like antigens at a high level, are dendritic in morphology, and represent cells of the macrophage/dendritic cell lineage. They are responsible for the formation of the epithelial bud which are then colonized by a small number of lymphoid precursors which belong to the CL-1+/L22+ lineage. Quail-chick bursa grafting experiments were also performed and the grafts were examined for CL-1 (restricted to chicken hemopoietic cells) and L22 reactivity. These observations confirmed our previous findings about the kinetics of the colonization of bursal rudiment by hemopoietic precursors and give support for a pre-bursal segregation between two hemopoietic pathways.

A chicken leukocyte common antigen: biochemical characterization and ontogenetic study

A monoclonal antibody, designated CL-1, was produced by immunizing mice with chicken peripheral blood lymphocytes (PBL) and selected in an indirect immunofluorescence assay. CL-1 characterizes a cell surface antigen expressed on all chicken hemopoietic cells except mature erythrocytes. Cells stained by CL-1 were detected at early stages of embryonic development in the various hemopoietic compartments. CL-1 reacts with two chicken PBL proteins of 200 kDa and 215 kDa which are probably the homologues of the T-200 and B-220 antigens previously described in the mouse. Moreover, CL-1 does not react with quail hemopoietic tissues and can be useful in experiments using quail-chick chimeras to study the ontogeny of the hemopoietic system.

The follicle-associated epithelium in the bursa of Fabricius cell origin studied by means of quail-chick chimeras and monoclonal antibodies

The cell origin of the follicle-associated epithelium (FAE) of the bursa of Fabricius was studied by two different technical approaches. Precolonized quail bursal rudiments were grafted into chick embryos and the grafts were recovered 2 wk after hatching of the recipients. By taking advantage of the distinct nuclear characteristics of chick and quail cells, it could be shown that the specialized FAE consists of a mixture of epithelial cells, with special features, among which hemopoietic cells, originating from the host, are dispersed. Staining of chicken bursas with different monoclonal antibodies reacting either with the epithelial component (BEP-1) or with the hemopoietic cells of the bursa (L22, L17) confirmed that hemopoietic cells, presumably macrophages, are mixed with the epithelial cells at the level of FAE.

The bursal microenvironment: phenotypic characterization of the epithelial component of the bursa of Fabricius with the use of monoclonal antibodies

Monoclonal antibodies were raised against newborn chick bursa of Fabricius, and here we describe two antibodies, BEP-1 and BEP-2, which react selectively with the epithelial component of the bursa of Fabricius. In previous studies, using quail chick chimeric bursas, we have demonstrated that the epithelium of the bursal rudiment, presumably of endodermal origin, gives rise to the epithelium lining the bursal lumen, the basement membrane-associated epithelium and the network of reticular cells of the medulla, while the interfollicular connective cells are derived from the mesoderm. When tested in indirect immunofluorescence assay on bursa tissue sections or cell suspensions, BEP-1 reacts with a surface antigen present on all the epithelial cells of the bursa and could be used as a marker for this cell lineage. BEP-2 binds to an intracytoplasmic antigen that is present in about 5% of cells, representing the epithelial cells, and which is excreted in the medulla. BEP-2 also reacts with the epithelial cells of the thymic medulla and with the mucin-secreting goblet cells of the intestinal villi. A rabbit antiserum raised against human cytokeratin gives a different pattern of reactivity on bursal tissue compared to BEP-1 and BEP-2, tentatively suggesting that these two antibodies do not bind to keratin-like molecules. During ontogeny, BEP-1 reactivity appears in bursal epithelium from the early stages of bursal ontogeny (8 days). BEP-2 reactivity is detected around hatching time. BEP-1 and BEP-2 do not show any antigenic heterogeneity among the epithelial cells of the bursa.

Split tolerance induced by chick embryo thymic epithelium allografted to embryonic recipients

To test the capacity of the epithelial component of the chick embryo thymus to induce tolerance to major histocompatibility complex (MHC) antigens, pre-colonized thymic rudiments were grafted into chick embryonic recipients. Semi-allogeneic or allogeneic transplantations were done between two lines of chickens histocompatible at the MHC locus. Approximately 10% of these thymic chimeras hatched and were studied 3 mo after hatching. Thymic grafts were not rejected by the allogeneic host. The tolerance of chimeric chickens to thymus donor MHC antigens was tested by using a skin graft rejection test and a graft-vs-host (GvH) assay. Chimeric chickens that received an MHC-incompatible thymic graft during the embryonic life tolerated skin graft with the MHC haplotype of the thymus donor. Nevertheless, the lymphocytes within the thymic graft, the host thymus, and the blood were tolerant to the host MHC antigens but were alloreactive in GvH reaction for the MHC antigens of the thymic graft type. These results suggest that the epithelial component of the thymus when taken before the starting of the colonization by hemopoietic precursors and grafted into an early chick embryonic host can induce a tolerance for the MHC determinants involved in allograft rejection but not in the GvH reaction.

Split tolerance induced by chick embryo thymic epithelium allografted to embryonic recipients

To test the capacity of the epithelial component of the chick embryo thymus to induce tolerance to major histocompatibility complex (MHC) antigens, pre-colonized thymic rudiments were grafted into chick embryonic recipients. Semi-allogeneic or allogeneic transplantations were done between two lines of chickens histocompatible at the MHC locus. Approximately 10% of these thymic chimeras hatched and were studied 3 mo after hatching. Thymic grafts were not rejected by the allogeneic host. The tolerance of chimeric chickens to thymus donor MHC antigens was tested by using a skin graft rejection test and a graft-vs-host (GvH) assay. Chimeric chickens that received an MHC-incompatible thymic graft during the embryonic life tolerated skin graft with the MHC haplotype of the thymus donor. Nevertheless, the lymphocytes within the thymic graft, the host thymus, and the blood were tolerant to the host MHC antigens but were alloreactive in GvH reaction for the MHC antigens of the thymic graft type. These results suggest that the epithelial component of the thymus when taken before the starting of the colonization by hemopoietic precursors and grafted into an early chick embryonic host can induce a tolerance for the MHC determinants involved in allograft rejection but not in the GvH reaction.

Tissue distribution and ontogenic appearance of a chicken T lymphocyte differentiation marker

A monoclonal antibody, designated T10A6, was produced by immunizing mice with H.B14 chicken thymocytes. T10A6, when tested by immunofluorescence, labeled 80% of thymocytes, and a subset of peripheral T cells: 20% of spleen leukocytes, 10% of blood leukocytes, 8% of bone marrow cells but less than 1% of bursal lymphocytes. Tissue distribution on polyethylene glycol sections showed that in the thymus T10A6 stained most cortical thymocytes and a portion of medullary cells. In the spleen, the positive cells appeared scattered mainly in the T-dependent areas. Ontogenic studies revealed that the antigen recognized was found in the chick embryo thymus from day 11 onward and the expression of this antigen on thymocytes reached the adult level from day 13. The first positive cells were detected in the spleen on day 13 of embryonic life. T10A6 (IgG1) precipitated a 65-kDa material from thymocytes. This is the first description of a monoclonal antibody recognizing a peripheral T cell subpopulation in chicken.

Post-natal ontogenesis of graft-versus-host reactivity of peanut agglutinin lectin-negative thymocytes in the chicken

Chicken thymocyte fractionation by peanut agglutinin lectin yields two cell subpopulations which differ in their GvH competence when injected into major histocompatibility complex (MHC)-(B locus) incompatible embryos. The nonagglutinated PNA- fraction displayed a degree of alloreactivity similar to that of peripheral blood lymphocytes while the PNA+ cells were nonreactive. Analysis of chickens at the age of 4 to 24 weeks showed that the development of GvH-reactive PBL preceded by 12 weeks the maturation of GvH-reactive PNA- thymocytes. Possible interpretations for this difference between the time of appearance of GvH reactivity of PNA- thymocytes and PBL are discussed.

Ontogenic restriction of colonization of the bursa of Fabricius

The capacity of hemopoietic precursor cells (HPC) to home to embryonic bursal and thymic grafts was investigated in embryonic and newly hatched chickens. Whereas thymic grafts developed normal histogenesis in both types of recipients, the bursal rudiment was colonized and developed in embryonic, but not in newly hatched hosts. In the latter, noncolonized bursal grafts developed neither lymphoid follicles nor granulopoiesis in the mesenchyme. These results are interpreted in terms of ontogenic "maturation" of the HPC which lose their homing potential towards the bursa while they preserve their thymic seeding capacity. This hypothesis is consistent with previously reported data which indicated cyclic continuous recruitment of the thymic lymphoid population, but restricted bursal colonization to a relatively brief period of embryonic life.

Differentiation of the mouse hepatic primordium. II. Extrinsic origin of the haemopoietic cell line

The whole hepatic primordium (endoderm + mesenchyme of the septum transversum) was isolated from mouse embryos at various developmental stages, from 8 to 10 days of gestation, and was either grafted into chick or quail embryo or cultivated in vitro. Haemopoiesis developed only if the liver rudiment had been explanted after the 28- to 30-somite stage, but not if explanted prior to this stage, despite normal differentiation of the hepatocytes. However, when the liver rudiment, isolated before the 28-somite stage in in vitro culture, was supplied with exogenous haemopoietic stem cells, haemopoiesis developed in the hepatic tissue. These data show that foetal hepatic haemopoiesis depends on migration of haemopoietic cells which home the liver rudiment at the 28- to 30-somite stage.

Ontogeny of the avian thymus and bursa of Fabricius studied in interspecific chimeras

Differences in the structure of the interphase nucleus between two species of birds, the Japanese quail (Coturnix coturnix japonica) and the chick (Gallus gallus) have been used to distinguish cells from different origins in interspecies combinations. This biological cell marking technique was applied to thymus and bursa of Fabricius histogenesis. Using various combinations between components of quail and chick thymic and bursic rudiments, the respective contribution of endodermal epithelium, mesenchyme and blood-borne extrinsic elements to the histogenesis of thymus and bursa was analyzed. It was demonstrated that the whole lymphoid population in these organs is derived from immigrant blood-borne stem cells. Thymus and bursa become attractive for stem cells at a precise stage of their development. In thymus the attractive period last about 24 hours in the quail and 36 hours in the chick. In the bursa of Fabricius the invasion lasts several days in both quail and chick embryos. The mechanisms which control the onset and the interruption of the stem cells inflow have been investigated.

[Reversibility of the morphological and functional dedifferentiation occurring in cultures of avian embryonic liver cells (author's transl)]

Primary cell cultures are established from 8-day quail embryo livers. During the first three days the culture is made up of areas of epithelial-like cells and scattered fibroblasts. The cytoplasm of the epithelial cells shows a high glycogen content as detected by the PAS reaction controlled with salivary amylase digestion. During the following days an important increase in the number of fibroblastic cells is observed. After 6-7 days of cultivation, the epithelial cells have disappeared and the culture is entirely fibroblastic. PAS technique does not show any trace of glycogen in these cultures which have been prolonged up to 45 days. Six-to 45-day primary cultures entirely made up of fibroblasts were associated with hepatic or pulmonary mesenchyme in organotypic culture for 3-4 days. In some cases the explant was first cultivated in vitro for 2 days and then grafted into a 5-day-old chick embryo on the chorioallantoic membrane for 6 days. In the secondary cultures hepatocytes showing an epithelial arrangement and a high glycogen content were observed. It appears from this observation that some of the primary culture fibroblasts are in fact dedifferentiated parenchymal cells. Such a dedifferentiation is a reversible phenomenon since the cells retain the ability to express their initial determination if they are placed in convenient environmental conditions. The role of the specific tissular arrangement in the stability of the differentiated state is discussed.