Generation of cytomegalovirus-specific human T-lymphocyte clones by using autologous B-lymphoblastoid cells with stable expression of pp65 or IE1 proteins: a tool to study the fine specificity of the antiviral response

Cytotoxic T lymphocytes (CTLs) play a central role in the control of persistent human cytomegalovirus (HCMV) infection in healthy virus carriers. Previous analyses of the specificity of HCMV-reactive CD8(+) CTLs drawn from in vitro models in which antigen-presenting cells were autologous fibroblasts infected with laboratory HCMV strains have shown focusing of CTL responses against the major tegument protein, pp65. By contrast, the 72-kDa major immediate-early protein (IE1) was identified as a minor target for this response. Here we have studied the fine specificity and T-cell-receptor features of T-cell clones generated against autologous B lymphoblastoid cell lines stably transfected with HCMV cDNA coding for either pp65 or a natural variant of IE1. This strategy allowed efficient generation of T-cell clones against IE1 and pp65 and led to the identification of several new IE1 and pp65 epitopes, including some located in polymorphic regions of IE1. Such an approach may provide relevant information about the characteristics of the CTL response to IE1 and the effect of viral polymorphism on the immune response against HCMV.

Implication of gammadelta T cells in the human immune response to cytomegalovirus

In normal individuals, gammadelta T cells account for less than 6% of total peripheral T lymphocytes and mainly express T-cell receptor (TCR) Vdelta2-Vgamma9 chains. We have previously observed a dramatic expansion of gammadelta T cells in the peripheral blood of renal allograft recipients only when they developed cytomegalovirus (CMV) infection. This increase was long lasting (more than 1 year), was associated with an activation of gammadelta T cells, and concerned only Vdelta1 or Vdelta3 T-cell subpopulations. Analysis of gammadelta TCR junctional diversity revealed that CMV infection in these patients was accompanied by (a) a marked restriction of CDR3 size distribution in Vdelta3 and, to a lesser extent, in Vdelta1 chains; and (b) a selective expansion of Vdelta1 cells bearing recurrent junctional amino acid motifs. These features are highly suggestive of an in vivo antigen-driven selection of gammadelta T-cell subsets during the course of CMV infection. Furthermore, Vdelta1 and Vdelta3 T cells from CMV-infected kidney recipients were able to proliferate in vitro in the presence of free CMV or CMV-infected fibroblast lysates but not uninfected or other herpes virus-infected fibroblast lysates. This in vitro expansion was inhibited by anti-gammadelta TCR mAb's. These findings suggest that a population of gammadelta T cells might play an important role in the immune response of immunosuppressed patients to CMV infection.

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.

The mechanism of chromosome 7 inversion in human lymphocytes expressing chimeric gamma beta TCR

Functional chimeric TCR chains, encoded by V gamma J gamma C beta or V gamma J beta C beta hybrid gene TCR, are expressed at the surface of a small fraction of alpha beta T lymphocytes in healthy individuals. Their frequency is dramatically increased in patients with ataxia-telangiectasia, a syndrome associated with inherited genomic instability. As the TCR gamma and beta loci are in an inverted orientation on chromosome 7, the generation of such hybrid genes requires at least an inversion event. Until now, neither the sequences involved in this genetic mechanism nor the number of recombinations leading to the formation of functional transcriptional units have been characterized. In this manuscript, we demonstrate that at least two rearrangements, involving classical recombination signal sequence and the V(D)J recombinase complex, lead to the formation of productive hybrid genes. A primary inversion 7 event between D beta and J gamma genic segments generates C gamma V beta and C beta V gamma hybrid loci. Within the C gamma V beta locus, secondary rearrangements between V gamma and J gamma or V gamma and J beta elements generate functional genes. Besides, our results suggest that secondary rearrangements were blocked in the C beta V gamma locus of normal but not ataxia-telangiectasia T lymphocytes. We also provide formal evidence that the same D beta-3' recombination signal sequence can be used in successive rearrangements with J gamma and J beta genic segments, thus showing that a signal joint has been involved in a secondary recombination event.

A polymorphism in the major immediate-early gene delineates groups among cytomegalovirus clinical isolates

Major immediate-early gene exon 4 sequences were determined at codons 161-241 and 254-397 in 25 cytomegalovirus clinical strains and compared with those of reference strains AD169 and Towne. The nucleotide sequences at codon 161-241 segregated into three groups which could be determined by restriction mapping of a 247-nucleotide amplified target. AD169 and Towne belonged to the same group. Clustered variations and group-specific amino-acid motifs found in the deduced peptide sequence of the two immediate-early (IE) exon 4 regions raised a question is to the effects of polymorphism on IE1 function and/or immunogenicity. On the basis of restriction analysis of polymerase chain reaction (PCR) products, virus isolates were also classified into four glycoprotein B (gB) genotypes. Strain distribution in IE1 and gB genotypes showed a lack of concordance of the two grouping methods, and no preferential association was observed between the clinical context or kind of specimen and IE1 or gB groups. These data lead up to further prospective studies which could provide important information on the implication of the MIE gene region in virus pathogenesis and indicate whether linkage unbalance exists in particular clinical contexts between IE1 and gB loci.

Acute graft-versus-host disease after bone marrow transplantation with a single HLA-DPB1*1001 mismatch: involvement of different TCRBV subsets

HLA-DP incompatibility is not considered as an exclusion criterion for bone marrow donors, because such incompatibility was not shown to affect significantly the risk for acute graft-versus-host disease (GVHD). In line with this clinical observation, it was proposed that in the context of bone marrow transplantation, HLA-DP determinants did not function as transplantation antigens in the same way as HLA-A, -B or -DR. In contrast to the above conclusion, we recently demonstrated the presence of HLA-DPB1*0501 specific T cell clones in a skin biopsy of a patient who developed aGVHD after receiving a bone marrow transplant (BMT) in which the only mismatched allele in the GVHD direction was HLA-DPB1*0501. At that time, this case was unique and occurred in a relatively uncommon graft setting where the patient received purified CD34+ BM cells from an unrelated donor. In the present study, we analyzed the immunological events associated with an aGVHD which occurred in the context of a 'regular' allogeneic BMT involving a single HLA-DPB1*1001 mismatch between donor and recipient in the GVHD direction. To this end, we analyzed several amplified T cell subsets present within a T cell line derived from a skin biopsy performed at the onset of GVHD. Our results demonstrated that T cell populations belonging to the TCRBV2, TCRB6.7, TCRBV14 and TCRBV17 subsets were specific for the HLA-DPB1*1001 mismatched allele. These data strengthen and generalize our first conclusion that a single HLA-DP mismatch between donor and recipient can activate a strong T cell response in vivo and consequently challenge the notion that HLA-DP incompatibility should not be taken into account in the choice of BM donors. Moreover, they also underline the idea that HLA-DP antigens may represent an interesting immune target for future therapeutic approaches.

Epitope-function relationships of human leukemia inhibitory factor receptors using a novel set of anti-gp190 mAB

The binding and functional properties of a set of six mAb directed against the human gp190 [leukemia inhibitory factor (LIF) receptor] signal transducing molecule were determined. Each of the antibodies reacted with a distinct epitope on gp190 expressed either by gp190-transfected Chinese hamster ovary cells or by the LIF receptor-positive choriocarcinoma JAR cell line. Two of the antibodies (1B4 and 6E6) had binding stoichiometries that were approximately 2-fold lower than those of other mAb (10B2, 12D9 and 7G7), suggesting either that gp190 is present as a pre-associated homodimer in the cell membrane or that part of gp190 is pre-associated with another component. Two mAb (1C7 and 1B4) were found to inhibit LIF binding on the two cell types studied. On JAR cells, this inhibition was, however, restricted to the high-affinity LIF component, suggesting different modes of LIF engagement with the low- and high-affinity receptor species. mAb 1C7 and 1B4 were also found to synergize for inhibiting LIF high-affinity binding. This synergy also extended to the inhibition of LIF- or oncostatin M (OSM)-induced proliferation of a Ba/F3 cell line co-transfected with human gp130 and gp190. However, this mAb combination inhibited LIF- but not OSM-induced haptoglobin secretion by HepG2 cells, suggesting that whereas haptoglobin secretion induced by LIF involves gp130/gp190 common LIF/OSM type I receptors, that induced by OSM mainly involves type II OSM receptors.

Reconstitution of two isoforms of the human interleukin-11 receptor and comparison of their functional properties

Long-term stable Ba/F3 transfectants (B13R alpha1 and B13R alpha2) expressing two isoforms of the human IL-IIR alpha receptor (alpha1 full length or alpha2 lacking the cytoplasmic domain) in combination with human gp130 were established. IL-11R alpha1 and IL-11R alpha2 were each expressed and detected as three bands upon Western blot analysis, with apparent molecular masses in agreement with those of the polypeptide backbone (47 and 44 kDa, respectively) with no, one or two N-linked sugars. B13R alpha1 and B13R alpha2 bound IL-11-thioredoxin with similar efficiencies and proliferated with superimposable dose-response curves to IL-11, demonstrating that the intracellular domain of IL-11R alpha has no significant contribution on ligand binding and signaling. Analysis of a set of anti-human gp130 mAbs confirmed the similar responsiveness of B13R alpha1 and B13R alpha2 transfectants.

Human HLA-specific T-cell clones with stable expression of a suicide gene: a possible tool to drive and control a graft-versus-host- graft-versus-leukemia reaction?

Allogeneic bone marrow transplantation is still limited by the morbidity and mortality caused by graft-versus-host disease (GVHD), resulting from host recognition by donor T lymphocytes. It is possible to drastically reduce the T-cell content of the graft. However, transplanted T cells can also have a beneficial effect by graft enhancement and the graft-versus-leukemia effect. How can we keep the beneficial GVL effect while protecting the patient from possible GVHD? A recent report proposed the ex vivo transfer of the herpes simplex thymidine kinase (HSv-tk) gene into donor T cells before their infusion with hematopoietic stem cells. This procedure is expected to allow selective donor T-cell depletion with ganciclovir should GVHD occur, but it has two major drawbacks: reinjection of a fraction of untransfected T cells cannot be avoided and heterogeneity of the transfected population results in increased risks such as HSv-tk gene instability or dysfunction of some of the transfected T cell. Alternative approaches must be considered. We demonstrate here the feasibility of generating HSv-tk transfected HLA-specific CD4+ cytotoxic T-cell clonal populations, in which 100% of the cells have the HSv-tk gene inserted at a single site within their genome. These clones retained their specificity, their function, and their sensitivity to ganciclovir treatment. Our approach is not limited to bone marrow transplantation. Indeed, this procedure represents a useful alternative to retroviral gene transduction and is applicable to every circumstance where clinical use of gene modified T-cell clones is to be considered.

A ciliary neurotrophic factor-sensitive human myeloma cell line

We obtained a human myeloma cell line (XG4-CNTF) whose growth was completely dependent on addition of ciliary neurotrophic factor (CNTF). Half-maximal proliferation was induced by adding 20 pg/mL CNTF. Response to CNTF correlated with expression of membrane CNTF receptor alpha-chain (CNTFR alpha), as shown by PCR analysis and immunostaining with anti-CNTFR alpha antibodies. CNTF-induced proliferation was completely inhibited by antibodies to gp130 interleukin-6 (IL-6) transducer, unlike antibodies to IL-6 or IL-6 receptor (IL-6R). Growth of XG4-CNTF cells using the gp130 IL-6 transducer was also supported by other cytokines: IL-6, leukemia inhibitory factor (LIF), and oncostatin M (OM). This cell line should be very useful for studying the interactions of IL-6-related cytokines with their receptors.

Acute graft versus host disease due to T lymphocytes recognizing a single HLA-DPB1*0501 mismatch

Analysis of a large number of unrelated bone marrow transplantations (BMT) has shown that HLA-DP incompatibility did not detectably influence the risk for acute graft-versus-host disease (aGVHD). Accordingly, it was proposed that HLA-DP determinants did not function as transplantation antigens in the same way as HLA-A, -B, or -DR. We have previously shown that HLA-DP (as well as HLA-A, -B, -DQ, or -DR)-specific T cells could be isolated from skin biopsies of patients who developed an aGVHD after semiallogeneic BMT. Nevertheless, whether a single HLA-DP mismatched allele could induce a detectable allo-specific reaction in vivo after BMT remained to be established. To directly address this issue we studied one patient who presented aGVHD after receiving purified CD34+ bone marrow (BM) cells from an unrelated donor with a single HLA-DP mismatch in the GVHD direction. To characterize the immunological events associated with GVHD, we analyzed the peripheral T cell repertoire, the T cell receptor Vbeta diversity, and the specificity of T cells invading a skin biopsy at the onset of GVHD. Our results demonstrated that a large fraction of skin-infiltrating lymphocytes, which expressed diverse T cell receptors, were reactive against this single HLA-DPB1 *0501 mismatch and consequently that a single HLA-DP mismatch between BM donor and recipient can activate a strong T cell response in vivo.

Anti-gp130 transducer monoclonal antibodies specifically inhibiting ciliary neurotrophic factor, interleukin-6, interleukin-11, leukemia inhibitory factor or oncostatin M

Five cytokines activate the gp130 IL-6 transducer: ciliary neurotrophic factor, interleukin-6, interleukin-11, leukemia inhibitory factor and oncostatin M. Human plasmacytoma cell lines, completely dependent on the addition of one of these five cytokines for their growth, were used to obtain anti-gp130 monoclonal antibodies specifically inhibiting one of these five cytokines without affecting the biological activity of the others. These antibodies should improve our understanding of the interaction of gp130 transducer using cytokines with gp130 transducer and facilitate the design of new cytokine inhibitors.

HLA-target antigens and T-cell receptor diversity of activated T cells invading the skin during acute graft-versus-host disease

To study the repertoire and specificity of T lymphocytes infiltrating skin lesions during graft-versus-host disease (GVHD), we performed an exhaustive molecular and functional analysis of 146 T-cell clones derived from the skin of three patients undergoing an acute GVHD after allogeneic bone marrow transplantation (BMT) from HLA-mismatched related donors. Analysis of T-cell receptor (TCR) rearrangement and TCR chain junctional sequences demonstrated the presence of 11 distinct clones among the 64 derived from patient UPN1, six among the 58 derived from patient UPN2, and seven among the 24 derived from patient UPN3. Three of the 11 T-cell clones from patient UPN1, and all clones from patients UPN2 and UPN3 reacted with mismatched HLA alleles between the bone-marrow donor and recipient. Moreover, both HLA class I (HLA-A2 and -B27) and class II (HLA DP101, DP401, DP1301, DQ8, and DR402) molecules were recognized during this early antihost response. Finally, both TCR alpha and beta chains turned out to be extremely diverse, even within populations of clones derived from the same patient and directed against the same HLA allele. Taken together, these results indicate that any HLA mismatch is potentially targeted during early GVHD, and that the T-cell response at the onset of GVHD is both oligoclonal and highly diversified.

Leukemia inhibitory factor (LIF) and oncastsin M (OSM) high affinity binding require additional receptor subunits besides GP130 and GP190

The structure of Leukaemia Inhibitory Factor (LIF) and Oncostatin M (OSM) receptors is not completely resolved. Heterodimerization of gp190 and gp130 has been proposed to form a high affinity receptor (type I) shared by LIF and OSM, while heterodimerization of gp130 with an as yet unidentified subunit is proposed to form a high affinity OSM receptor (type II) not shared by LIF. We have analysed the binding stoichiometries, cross-competition properties and cross-linking patterns of LIF and OSM to the choriocarcinoma JAR cell line. The data obtained are not fully accounted for by the model proposed above. They indicate rather that third chains of 140-150 kDa molecular mass, in addition to the gp130 and gp190 subunits, enter in the structure of LIF and OSM high affinity receptors. These results were strongly supported by transfection experiments in CHO cells. CHO cells co-transfected with the human gp190 and gp130 cDNAs expressed high affinity LIF receptors but no high-affinity OSM receptors, indicating that an additional component is required for high affinity OSM binding. High-affinity LIF cross-linking on these cells also showed the association of LIF with a 150 kDa component in addition to the gp130 and gp190 subunits.

Structural analysis of gamma delta TCR using a novel set of TCR gamma and delta chain-specific monoclonal antibodies generated against soluble gamma delta TCR. Evidence for a specific conformation adopted by the J delta 2 region and for a V delta 1 polymorphism

We recently showed that secretion of non-chimeric disulfide-linked human gamma delta TCR ('soluble' TCR, sTCR) comprising V gamma 9 and V delta 2 regions could be achieved by simply introducing translational termination codons upstream from the sequences encoding TCR transmembrane region. Here we extended these findings by demonstrating efficient secretion and heterodimerization of gamma delta sTCR comprising V gamma 8, V delta 1 and V delta 3 regions, obtained via the same strategy. After immunization against immunoaffinity-purified soluble TCR, several hundreds of TCR-specific monoclonal antibodies (mAb) were generated, which fell in at least seven groups. One set of mAb was directed against a V gamma 8-specific epitope. Strikingly, despite the high degree of sequence homology between V gamma 8 and other V gamma I domains, none of these mAb were crossreactive with other members of the V gamma I family. Three other sets of mAbs were shown to recognize delta chains comprising V delta 1, V delta 2 and V delta 3 regions respectively, regardless of their junctional sequence or of the gamma chain to which they were paired. Among the V delta 1-specific mAb, some specifically recognized V delta 1D delta J delta C delta chains while others reacted with both V delta 1 D delta J delta C delta and V delta 1J alpha C alpha chains, which suggested V domain conformational alterations induced by the C region. Moreover, reactivity of one V delta 1-specific mAb (#R6.11) was affected by a polymorphic residue located on the predicted CDR4 loop of the V delta region. Two delta chain-specific mAb (#178 and #515) showed a highly unusual reactivity, which was negatively affected by particular V delta and J delta sequences: (i) mAb #515 and #178 recognized all TCR delta chains except those comprising V delta 1 or V delta 2 regions, respectively and (ii) within TCR delta chains carrying 'permissive' V delta regions, none of those comprising the J delta 2 region were recognized by #515 and/or #178 mAbs, which suggested a highly specific conformation adopted by this particular J delta sequence. Apart from its usefulness in TCR structural studies, this novel set of mAb represents an important tool for the characterization and isolation of gamma delta T cells expressing particular combinations of V gamma/V delta regions and for analysis of V alpha/V delta usage by alpha beta T cells. Moreover, since our present data strongly suggest that gamma delta TCR are easier to obtain in a soluble form than alpha beta TCR, an efficient strategy for the generation of V alpha region-specific mAb might be to immunize with chimeric gamma delta sTCR comprising particular V alpha regions.

Alterations of T cell repertoire after bone marrow transplantation: characterization of over-represented subsets

We recently demonstrated that frequencies of T cell receptor-V (TcR-V)-specific subsets are frequently altered after both allogeneic and autologous BMT. The data reported here describe several characteristics of altered T cell subsets: (i) their capacity to endure peripherally, (ii) their correspondence to clonal donor T cell subsets, (iii) the origin of the clone (in one case amenable to analysis) from a mature T cell and not from new lymphopoiesis, and (iv) the presence of such a clone throughout a year of follow-up in a patient with chronic graft-versus-host disease (GVHD) in whom it represented up to 1/10th of CD3+ peripheral blood lymphocytes (PBL) and was found to be host-reactive. Taken together, these findings provide direct evidence for the oligoclonality of a large proportion of the peripheral T cell repertoire in patients subsequent to bone marrow transplantation, possibly accounting for their frequent depressed immune status. Moreover, the anti-host reactivity demonstrated in a clone from the patient with chronic GVHD strongly suggests that an oligoclonal response can be linked to a pathological process.

Dual T cell receptor beta chain expression on human T lymphocytes

Allelic exclusion of lymphocyte antigen receptor chains has been hypothesized as a mechanism developed by the immune system to ensure efficient lymphocyte repertoire selection and tight control of lymphocyte specificity. It was effectively shown to be operative for both the immunoglobulin (Ig) and the T cell receptor (TCR) beta chain genes. Our present observations suggest that close to 1% of human T lymphocytes escape this allelic control, and express two surface TCR beta chains with distinct superantigenic reactivities. Since this high frequency of dual beta chain expressors did not result in any dramatic immune dysregulations, these results question the need for a mechanism ensuring clonal monospecificity through allelic exclusion.

Surface expression of functional T cell receptor chains formed by interlocus recombination on human T lymphocytes

Structural diversity of lymphocyte antigen receptors (the immunoglobulin [Ig] of B cells and the alpha/beta or gamma/delta T cell receptor [TCR] of T cells) is generated through somatic rearrangements of V, D, and J gene segments. Classically, these recombination events involve gene segments from the same Ig or TCR locus. However, occurrence of "trans" rearrangements between distinct loci has also been described, although in no instances was the surface expression of the corresponding protein under normal physiological conditions demonstrated. Here we show that hybrid TCR genes generated by trans rearrangement between V gamma and (D) J beta elements are translated into functional antigen receptor chains, paired with TCR alpha chains. Like classical alpha/beta T cells, cells expressing these hybrid TCR chains express either CD4 or CD8 coreceptors and are frequently alloreactive. These results have several implications in terms of T cell repertoire selection and relationships between TCR structure and specificity. First, they suggest that TCR alloreactivity is determined by the repertoire selection processes operating during lymphocyte development rather than by structural features specific to V alpha V beta regions. Second, they suggest the existence of close structural relationships between gamma/delta and alpha/beta TCR and more particularly, between V gamma and V beta regions. Finally, since a significant fraction of PBL (at least 1/10(4)) expressed hybrid TCR chains on their surface, these observations indicate that trans rearrangements significantly contribute to the combinatorial diversification of the peripheral immune repertoire.

Characterization of a new functional TCR J delta segment in humans. Evidence for a marked conservation of J delta sequences between humans, mice, and sheep

Through analysis of TCR delta-chain cDNA derived from human gamma delta T cell clones and polyclonal gamma delta T cell lines, we isolated a novel functional J delta gene segment (termed J delta 4) whose genomic fragment has been mapped within the TCR-delta locus between J delta 2 and J delta 1. Frequency of J delta 4 use was estimated among adult gamma delta PBL by using V delta 1, V delta 2, and V delta 5 genes. In all cases, this new J element was used at a low, albeit significant frequency, close to that of J delta 2. Finally, like human J delta 1 and J delta 2, which show a high degree of homology with their counterparts in the mouse and sheep, but unlike other J gamma, J beta, or J alpha elements, J delta 4 turned out to be highly homologous to a recently described ovine J delta. These results suggest the existence of strong selective pressures, possibly linked to an Ag-driven process, leading to specific conservation of J delta sequences among these three species.

Characterization of a new functional TCR J delta segment in humans. Evidence for a marked conservation of J delta sequences between humans, mice, and sheep

Through analysis of TCR delta-chain cDNA derived from human gamma delta T cell clones and polyclonal gamma delta T cell lines, we isolated a novel functional J delta gene segment (termed J delta 4) whose genomic fragment has been mapped within the TCR-delta locus between J delta 2 and J delta 1. Frequency of J delta 4 use was estimated among adult gamma delta PBL by using V delta 1, V delta 2, and V delta 5 genes. In all cases, this new J element was used at a low, albeit significant frequency, close to that of J delta 2. Finally, like human J delta 1 and J delta 2, which show a high degree of homology with their counterparts in the mouse and sheep, but unlike other J gamma, J beta, or J alpha elements, J delta 4 turned out to be highly homologous to a recently described ovine J delta. These results suggest the existence of strong selective pressures, possibly linked to an Ag-driven process, leading to specific conservation of J delta sequences among these three species.

Alteration of the T cell repertoire after bone marrow transplantation

We investigated T cell receptor (TCR) alpha/beta and gamma/delta repertoire reconstitution after autologous and allogeneic bone marrow transplantation (BMT) in humans using 13 monoclonal antibodies directed at constant and variable regions of the TCR. The TCR gamma/delta repertoire was studied kinetically during the first month and then 1 year post-BMT whereas alpha/beta peripheral blood T lymphocytes (PBTL) were studied within the first 3 months and 1 year post-BMT. Through these two studies, we found 7 of 26 patients with over-represented TCR gamma/delta subsets during the early period post-BMT. Moreover, during this period the V gamma 9V delta 2 frequency among gamma/delta T cells was found to be higher than among normal donors. Study on TCR alpha/beta T cells also revealed abnormally expanded V-specific subset (5 of 10 patients within 3 months following BMT) demonstrating that repertoire alteration early after BMT is a general phenomenon concerning potentially all T cell subsets. More surprisingly, the alpha/beta T cell repertoire was also found to be altered late after BMT (7 of 15 patients after 1 year post-BMT presented one or more overepresented alpha/beta TCR subset). These alterations of TCR combinatorial diversity should be taken into account in understanding the immunological status of patients after BMT.

Close correlation between Daudi and mycobacterial antigen recognition by human gamma delta T cells and expression of V9JPC1 gamma/V2DJC delta-encoded T cell receptors

Recent studies have demonstrated that a large fraction of human gamma delta PBL recognize Ag of prokaryotic and eukaryotic origins, respectively found in hydrosoluble mycobacterial extracts and on the Daudi Burkitt's lymphoma cells. The structural basis of the recognition of these Ag have been presently studied in detail, through analysis of a large panel of thymus- and peripheral blood-derived gamma delta T-cell clones. Our results suggest that Daudi and mycobacteria-reactive gamma delta subsets are strictly overlapping and hence that gamma delta T-cell responses against these two Ag are closely related. Daudi cells and mycobacteria were recognized by V gamma 9+V delta 2+, but not by V gamma 9+V delta 2-, V gamma 9-V delta 2+, or V gamma 9-V delta 2- PBL clones. However, not all V gamma 9+V delta 2+ clones were reactive and, in particular: 1) the proportion of Ag-reactive lymphocytes was much lower among thymus- than PBL-derived clones (respectively 24/36 vs 72/73); 2) none of the V gamma 9+V delta 2+ clones expressing a V9J2C2 gamma chain (n = 4) were reactive to Daudi or mycobacteria, indicating that expression of a disulfide-linked TCR is probably a prerequisite for recognition of these Ag; and 3) among V gamma 9+V delta 2+ clones bearing disulfide-linked TCR, almost all (50/53) clones expressing a V9JPC1 gamma chain were reactive, whereas a large fraction (6/10) of those expressing a V9J1C1 gamma chain were weakly or nonreactive. Together, these observations suggest that germline residues specific to V gamma 9, V delta 2, and J gamma P elements directly contribute to recognition of Daudi and mycobacterial Ag. Furthermore, these findings may provide an explanation for coordinate use of these gene elements by a large fraction of gamma delta PBL, through peripheral selection events mediated by ligands identical or structurally related to the above Ag.

Close correlation between Daudi and mycobacterial antigen recognition by human gamma delta T cells and expression of V9JPC1 gamma/V2DJC delta-encoded T cell receptors

Recent studies have demonstrated that a large fraction of human gamma delta PBL recognize Ag of prokaryotic and eukaryotic origins, respectively found in hydrosoluble mycobacterial extracts and on the Daudi Burkitt's lymphoma cells. The structural basis of the recognition of these Ag have been presently studied in detail, through analysis of a large panel of thymus- and peripheral blood-derived gamma delta T-cell clones. Our results suggest that Daudi and mycobacteria-reactive gamma delta subsets are strictly overlapping and hence that gamma delta T-cell responses against these two Ag are closely related. Daudi cells and mycobacteria were recognized by V gamma 9+V delta 2+, but not by V gamma 9+V delta 2-, V gamma 9-V delta 2+, or V gamma 9-V delta 2- PBL clones. However, not all V gamma 9+V delta 2+ clones were reactive and, in particular: 1) the proportion of Ag-reactive lymphocytes was much lower among thymus- than PBL-derived clones (respectively 24/36 vs 72/73); 2) none of the V gamma 9+V delta 2+ clones expressing a V9J2C2 gamma chain (n = 4) were reactive to Daudi or mycobacteria, indicating that expression of a disulfide-linked TCR is probably a prerequisite for recognition of these Ag; and 3) among V gamma 9+V delta 2+ clones bearing disulfide-linked TCR, almost all (50/53) clones expressing a V9JPC1 gamma chain were reactive, whereas a large fraction (6/10) of those expressing a V9J1C1 gamma chain were weakly or nonreactive. Together, these observations suggest that germline residues specific to V gamma 9, V delta 2, and J gamma P elements directly contribute to recognition of Daudi and mycobacterial Ag. Furthermore, these findings may provide an explanation for coordinate use of these gene elements by a large fraction of gamma delta PBL, through peripheral selection events mediated by ligands identical or structurally related to the above Ag.

Secretion of disulfide-linked human T-cell receptor gamma delta heterodimers

The availability of soluble forms of T-cell antigen receptors (sTCR) should be of great use in the detailed characterization of their interactions with ligands, for the generation of anti-TCR monoclonal antibodies (mAb), and for the eventual determination of their three-dimensional structures by x-ray crystallography. Here, we show that efficient secretion of nonchimeric disulfide-linked human gamma delta TCR could be achieved by simply introducing translational termination codons upstream from the sequences encoding TCR chain transmembrane regions. This recombinant protein appeared to be correctly folded, as judged by its reactivity with a panel of anti-gamma and anti-delta mAbs, and proved to be a powerful immunogen, allowing generation of mAb that are able to recognize both soluble- and membrane-bound gamma delta TCR. While variable and constant domains of gamma delta sTCR seem to be folded into compact conformations, the extreme sensitivity of its interchain disulfide bridge to digestion with papain suggests that sTCR C-terminal portions are in a more extended configuration than the corresponding region in immunoglobulins. Finally, the gamma delta heterodimer remains stable even after removal of the interchain disulfide link, suggesting the existence of strong noncovalent forces holding the two chains together.

Surface expression of two distinct functional antigen receptors on human gamma delta T cells

Lymphocytes recognize antigens with highly variable heterodimeric surface receptors. Although four distinct antigen receptors could in principle be produced by any lymphocyte, only one functional combination of receptor chains has thus far been found expressed on their surface. Examination of human gamma delta T cells revealed a population that violated this rule by expressing on their surface two distinct functional gamma delta T cell receptors (TCRs) that used different TCR gamma gene alleles. Thus, current models for T cell clonal selection may need modification, and a possible escape mechanism for autoreactive TCRs is suggested.

Peripheral selection of antigen receptor junctional features in a major human gamma delta subset

Recent studies demonstrating the existence of murine gamma delta T cell subsets with structurally identical T cell receptors (TcR) suggest that unlike alpha beta T cells, some gamma delta T cells are specialized in the recognition of a limited number of monomorphic antigens. However, this question still remains open in humans, since the TcR structural diversity of their peripheral gamma delta T cells was shown to be extensive. Here we have analyzed in detail the TcR chain genes expressed by human V gamma 9+V delta 2+ peripheral blood lymphocytes (PBL), a major peripheral gamma delta T cell subset in adults and present evidence for an antigen-driven peripheral selection of both TcR gamma and delta junctional motifs among these cells. First, it is shown that the proportion of V gamma 9+V delta 2+ cells expressing the V9JPC1 gamma chain is much higher among PBL than among thymus-derived clones, indicating that preferential use of this J gamma segment is not due to pairing or combinatorial constraints. Second, analysis of V9JPC1 gamma transcripts derived from V gamma 9+V delta 2+ PBL clones revealed a high prevalence of a unique V9JP gamma sequence with limited "N" nucleotide additions and VJ trimming, which could not be accounted for by enzymatic or antigen-independent structural limitations. Third, the TcR delta chain expressed by most V gamma 9+V delta 2+ PBL clones, though diverse in amino acid composition and length, carried a highly distinctive junctional motif, found at a much lower frequency among V2DJ delta sequences derived from V gamma 9-V delta 2+ PBL or V gamma 9+V delta 2+ thymocytes. Together, these results which demonstrate shared gamma and delta junctional features by cells using unique V gamma and V delta genes, suggest that in vivo selection of V gamma 9+V delta 2+ lymphocytes is mediated by a highly restricted number of nominal ligands.

The effects of cyclosporine on HILDA/LIF gene expression in human T cells

We examined the effect of cyclosporine on HILDA/LIF gene expression in alloreactive human T lymphocyte clones (ATLCs) 2B11 and 2F7 obtained from cells infiltrating a rejected human kidney graft. Both ATLCs were stimulated either by the specific antigen or by PMA + calcium ionophore in the presence of various concentrations of CsA (10-500 ng/ml). Inhibition of HILDA/LIF gene expression was analyzed at the protein level using a proliferative assay on the HILDA/LIF-dependent Da-1a cell line and by RNA blotting using a specific probe. Without CsA, the kinetics of mRNA accumulation for both ATLCs peaked at 5 and 10 hr, respectively, after mitogenic and antigenic stimulations. HILDA/LIF activity peaked at 24 and 72 hr, respectively, after mitogenic and antigenic stimulation in supernatants from both ATLCs and decreased thereafter. Subsequent experiments with CsA were thus performed at these time points. Our results show that HILDA/LIF mRNA accumulation and protein secretion in 2B11 and 2F7 clones were strongly inhibited in a dose-dependent manner by CsA, in both stimulation conditions. Maximal inhibition of HILDA/LIF transcripts and protein secretion (60-90%) was observed within the range of 75-500 ng/ml CsA.

Specificity of T cells invading the skin during acute graft-vs.-host disease after semiallogeneic bone marrow transplantation

The mechanisms responsible for skin lesions during acute graft-vs.-host disease (aGVHD) after allogeneic bone marrow transplantation (BMT) are poorly understood. The exact role of various effector cell populations and "major" (particularly HLA-DP) or "minor" antigens as target molecules is not known. To investigate the nature of cells responsible for tissue injury, we cultured T cells from skin biopsy first with interleukin 2 (IL-2) alone and then in polyclonal activation conditions to avoid in vitro antigenic sensitization before specificity testing. We applied this method to two biopsies performed during aGVHD after semiallogeneic BMT and obtained cytotoxic T cells against four graft mismatches: CD8+ T cells against HLA-A2.2 and HLA-B27 and CD4+ T cells against HLA-DP101 and HLA-DP401. This demonstrates that T cells with documented specificity can be obtained from an aGVHD lesion without antigenic selection. Moreover, these data directly implicate DP as a potential target antigen for aGVHD.

Simultaneous transcription of eleven cytokines in human alloreactive T lymphocyte clones after stimulation by phorbol ester and A23187

Human alloreactive T lymphocyte clones derived from cells invading a rejected kidney allograft, were analyzed for their ability to transcribe eleven cytokine genes under phorbol ester (PMA) plus calcium ionophore (CaI A 23187) stimulation. In addition to the positive signal previously obtained for IL-2 transcripts, strong specific patterns were seen with cytoplasmic dot hybridizations for IFN gamma and GM-CSF mRNAs in all the 17 clones screened. For the remaining transcripts (IL-3, IL-4, IL-5, IL-6, TNF alpha, LT, M-CSF and HILDA/LIF), these techniques proved to be inadequate. Northern-blots were therefore performed on three clones exhibiting different phenotypes (CD4+ CD8- non cytotoxic, CD4+ CD8- cytotoxic and CD4- CD8+ cytotoxic). Positive specific signal with the eleven probes could be obtained. Nevertheless, the IL-6 message was found only in the helper clone and the TNF alpha transcript appeared at a later time point compared to the other cytokine messages (its maximum expression was observed around 24 hours post-stimulation). In conclusion, we demonstrate that under PMA+CaI activation, one clone is able to simultaneously transcribe at least eleven lymphokine genes. Except, perhaps for IL-6, the pattern of lymphokine transcription did not permit us to distinguish between different lymphocyte subsets.

Peripheral tolerance of an allograft in adult rats--characterization by low interleukin-2 and interferon-gamma mRNA levels and by strong accumulation of major histocompatibility complex transcripts in the graft

Congenic LEW.1W(RT1.u) heart grafts in LEW.1A(RT1.a) recipient rats are rejected in 15 +/- 6 days. Tolerance (greater than 100 days) can be induced by pretransplant donor-specific blood transfusion. In this case, the graft is not rejected, although it is infiltrated by mononuclear cells specifically cytotoxic, in vitro, against allogeneic donor splenocytes. We studied the expression of MHC class I and class II antigens, IFN-gamma, and IL-2 mRNA in the rejected and tolerated grafts by Northern blotting and in situ hybridization. Our data show that both class I and class II mRNA accumulate in both types of graft, and that class I mRNA accumulation occurs more rapidly in the tolerated grafts. IFN-gamma and IL-2 mRNA accumulate to lower levels and with delayed kinetics in the tolerated grafts compared with the rejected ones, suggesting a role for these lymphokines in the mechanism of rejection/tolerance in this model. This hypothesis is also supported by the observation that IFN-gamma treatment abrogates the induction of tolerance in the recipients receiving pretransplant donor blood transfusion. Furthermore, we observed an uncoupling of the accumulation of IFN-gamma mRNA and of MHC class I and class II mRNA. Our data confirm that the mechanisms of tolerance in this model depend, in part, on alterations of the IL-2/IL-2R pathway of lymphocyte activation but also clearly indicate a decrease of IFN-gamma mRNA accumulation, suggesting that the defect involves several activation molecules.

Macrophage colony-stimulating factor (CSF-1) gene expression in human T-lymphocyte clones

Macrophage colony stimulating factor (CSF-1) is one of several cytokines that control the differentiation, survival, and proliferation of monocytes and macrophages. A set of 11 human T-cell clones, chosen for their phenotypic diversity, were tested for their ability to express CSF-1 mRNA. After 5 hours of stimulation with phorbol myristate acetate (PMA) + calcium ionophore (Cal), all T-cell clones expressed a major 4-kb transcript, a less abundant 2-kb transcript, and several other minor species. This pattern of expression is typical for CSF-1 mRNAs. Furthermore, of the two alloreactive T-cell clones analyzed, only one showed a definitive message for CSF-1 on specific antigenic stimulation, but with delayed kinetics and less efficiency. Both conditions of stimulation induced the release of CSF-1 protein by T cells in the culture medium. Together, these findings demonstrate for the first time that normal T cells are able to produce CSF-1, previous reports being limited to two cases of tumoral cells of the T-cell lineage.

Production of human interleukin for DA cells (HILDA)/leukemia inhibitory factor (LIF) by activated monocytes

We demonstrate mRNA accumulation and production of HILDA/LIF by human activated Mo, monocyte-derived macrophages and myelomonocytic cell lines. Among the various stimuli tested, the synergistic combination of phorbol diester and VD3 was the most potent inducer of HILDA/LIF gene expression. The kinetics of mRNA accumulation on activated Mo showed a stimulation peak at 24 hr which declined thereafter. HILDA/LIF activity in culture supernatants was detected at 24 hr and reached a plateau at 72 hr of culture. In contrast to Mo, PBL did not accumulate HILDA/LIF mRNA upon culture with PDBu and VD3, whereas PHA and the combination of PDBu and A23187 induced HILDA/LIF mRNA accumulation and secretion in the culture supernatant. To exclude the possibility that HILDA/LIF was produced by contaminating PBL, highly enriched Mo preparations were used, which were devoid of T cells as assessed by the absence of TCR-beta chain mRNA transcripts. HILDA/LIF production by monocytic cells was further documented by the capacity of stimulated U937 cell conditioned medium to compete with 125I-labeled nHILDA/LIF for binding to its receptor on murine M1 cells. Under the synergistic effect of PDBu and VD3 stimulation, Mo-derived macrophages as well as HL-60 and U937 cell lines accumulated HILDA/LIF mRNA and produced this cytokine with identical kinetics as for Mo. Finally, we show that HILDA/LIF mRNA accumulation in U937 cells upon stimulation with PDBu, or the combination of PDBu and VD3, was inhibited in the presence of the protein synthesis inhibitor CHX. These results document for the first time that human Mo, when stimulated appropriately in vitro, can express the HILDA/LIF gene and its product, and that intermediate proteins must be newly synthesized in this process.

Characterization of skin-infiltrating T lymphocytes during acute graft-versus-host disease

A panel of 34 clones was established from a cell line derived from the skin biopsy of a patient (genotype: A1, A2, B7, B8, DR3, DR6) undergoing acute graft-versus-host disease after semiallogeneic bone marrow transplantation with his mother's bone marrow (genotype: A1, A1, B7, B8, DR3, DR6). The T-cell line obtained presented the following phenotype: CD3+, CD4+, CD8-, CD16-, WT31+, T-cell receptor delta 1-, 4B4+, 2H4-, CD25+, DR+. This CD4+ T-cell line was poorly cytotoxic against the target cells tested, including the mother's phytohemagglutinin blasts as a negative control (autologous T cells), the father's phytohemagglutinin blasts bearing the mismatch haplotype, K562, U937, SVK14 (a keratinocyte cell line), and a panel of B-lymphoblastoid cell lines bearing HLA-A2, the known mismatch antigen. All but 1 of the 34 clones obtained were of CD4+ phenotype, and none was CD16+. Only the sole CD8+ clone showed significant cytotoxicity against the father's phytohemagglutinin blast; however, this cytotoxic activity was associated with the highest score for nonspecific killing against both K562 and U937. This work demonstrates the feasibility of obtaining a large panel of clones from a graft-versus-host disease target organ to constitute the basic cellular material for in vitro study of the graft-versus-host process.

Immune repertoire of graft-invading T cells

The immune repertoire of T lymphocytes invading human allografts is of fundamental importance both at the operational level, in order to achieve relevant matching, and at the functional level, since the unique capacity of T and B cells to specifically recognize allogeneic components restricts the origin of the signals leading to rejection by these cells. In this paper, the authors review their own work, as well as other contributions in this domain, with special reference to the frequency and function of donor-committed cells among the infiltrate and the relationship between T-cell receptor gene rearrangements and repertoire.

Proliferation dependence and production of IL-2 in human alloreactive T-cell clones

Human alloreactive T-cell clones derived from cells invading a rejected kidney allograft were found to be capable of proliferating upon specific antigenic stimulation in short term assays and in the absence of exogenous IL-2. In most culture supernatants there was no evidence of any activity capable of triggering proliferation of the murine IL-2-sensitive CTL-L2 line. The ability of these clones to produce IL-2 was investigated under several experimental conditions. A combination of phorbol ester plus calcium ionophore was very efficient in all clones tested (17/17) in inducing transcription of the IL-2 gene. Conversely, when cell activation took place through the CD3/Ti complex, we regularly failed to detect hu-IL-2 transcripts even when the number of stimulator cells was increased. However, a blockade of IL-2-R with a monoclonal antibody inhibiting ligand receptor interaction while decreasing proliferation induced by the antigen in dose-dependent fashion permitted the presence of IL-2 to be demonstrated in supernatants. These results strongly suggest that IL-2-driven proliferation is essential in this model and may represent a major, although not exclusive, pathway leading to proliferation of these clones.

Interleukin 2-like material in human epidermis: a ligand for the human interleukin 2-receptor 55 kD alpha chain

The antirecombinant interleukin 2 (rec-IL-2) monoclonal antibody (moAb) 15.2 cross-reacts with a skin antigen located at the cell surface of human keratinocytes within the granular layer. This study extends the analysis of this IL-2-like material to its reactivity with eight antibodies raised against natural IL-2, rec-IL-2 or IL-2 peptides. Four among them were found to react with the granular epidermal layer as well as with a simian virus 40 (SV40) transformed human keratinocyte cell line. Each of these four antibodies gave similar labeling patterns, although with different intensities, and competitively inhibited each other. Analysis at the messenger RNA level in epidermal cells and SVK 14 also indicated that this material is very likely different from IL-2. From the knowledge, for some of these antibodies, of the amino-acid regions they recognize on the IL-2 molecule, it is inferred that the skin antigen shares with IL-2 at least two overlapping epitopes located in the 33-54 amino-acid region of IL-2, a region that has been shown to be involved in the binding of IL-2 to the IL-2-receptor (IL-2-R) 55 kD chain. Indeed, a purified recombinant soluble species of this IL-2-R is shown in this study to bind specifically to the IL-2-like skin material. As far as IL-2-R bearing cells are found in normal epidermis (Langerhans cells) and as important infiltrates of IL-2-R positive T lymphocytes are often encountered in cutaneous diseases, a potential role for this IL-2-like material in skin immunophysiopathology is suggested.

Effect of cyclosporine on interleukin 2 receptor expression in a human alloreactive T cell clone

The effect of CsA on antigen-induced IL-2 receptor expression was studied on a human T lymphocyte clone (4AS) obtained from cells infiltrating a rejected human kidney. Stimulation of 4AS clone cells with specific antigen (D.BLCL) was strongly inhibited by CsA (50% inhibition of tritiated thymidine uptake at about 12.5 ng/ml). Addition of recombinant IL-2 only partially restored 4AS growth inhibition, suggesting that another antigen-induced activation signal such as IL-2-receptor expression could be impaired by CsA. Using 125I-labeled human recombinant IL-2 and 125I-labeled 33B3.1 (a MoAb directed against TAC antigen), we found that expression of both high and low affinity sites was decreased when clone cells were stimulated with D.BLCL in the presence of CsA and exogenous IL-2 (about 50% inhibition in the presence of 500 ng/ml of CsA). Northern blot analysis of IL-2-receptor m.RNA (TAC antigen m.RNA) showed that inhibition occurred at least in part at the pretranscriptional level.

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.

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.

Quail melanoblast migration in two breeds of fowl and in their hybrids: evidence for a dominant genic control of the mesodermal pigment cell pattern through the tissue environment

In the Silkie fowl large numbers of melanocytes invade most internal tissues and organs. The factors involved in this internal pigment cell pattern were studied by grafting quail neural tube segments into White Leghorn, White Silkie, and F1 hybrids (White Silkie male X White Leghorn female). Sections of quail neural tube five somites long, excised at the level of the last formed somites, were grafted isotopically and ischoronically. Various tissues and organs (mesenteries, muscles, testis, ovary, mesonephros, metanephros, and adrenals) excised from the internal region corresponding to the peripheral transverse strip of quail melanocytes, were studied after staining by the Feulgen-Rossenbeck technique. Despite some variations in pigment cell density, Silkie and hybrid grafted embryos exhibited an extensive quail internal pigmentation similar to the melanocyte distribution in the Silkie breed. In white Leghorn host embryos, the internal pigmentation remained limited. These results show the part played by tissular factors in the expression of the Silkie pigment phenotype and that this genetic tissular character is dominant. On the contrary, White Leghorn embryos, grafted with Silkie neural tube segments, never exhibited any internal pigmentation; the melanocytes deriving from the grafted Silkie neural tube were only localized at the dermoepidermal level. Thus, the migrating and/or differentiating capabilities of the Silkie premelanoblasts are different from those of quail premelanoblasts. The sex-linked inhibitor of the White Leghorn tissue interferes at the level of the pigment cells of chickens but not of quails.