Isolation of mouse small intestinal intraepithelial lymphocytes, Peyer's patch, and lamina propria cells

The intestinal mucosal immune system is composed of three major lymphoid areas: the lamina propria (LP), which lies just underneath the basement membrane in the intestinal villi; (2) the intraepithelial compartment, which contains the intraepithelial lymphocytes (IEL) and is located just above the basement membrane, between the columnar epithelial cells; and (3) Peyer's patches (PP), lymphoid nodules (akin to lymph nodes) embedded in the gut wall, separated from the LP and IEL. The LP, PP, and IEL lymphoid populations form a complex, interconnected network that responds to immunological insults in the intestine. Therefore, these lymphocyte populations should be analyzed when studying the immunological status of the intestine, for example in oral immunization or in intestinal disease (including infectious disease and tumors). This unit details techniques for isolation of IEL, PP cells, and LP cells from the small intestine of the mouse.

Novel IL-15 isoforms generated by alternative splicing are expressed in the intestinal epithelium

Previous studies have identified mRNA three isoforms encoding interleukin-15 (IL-15) that are produced through differential splicing and encode for the same mature IL-15 protein with two different signal peptides. Our analysis of mouse intestinal epithelial cells revealed two new IL-15 mRNA isoforms generated by different alternative splicing events. In one form (IL-15DeltaE6), exon 6 is absent, and in the second form the first 48 nt of exon 7 are absent (IL-15DeltaE7) through usage of an alternative 5' splicing site within exon 7. These mRNA isoforms encoded in-frame IL-15 protein variants lacking either 15aa (IL-15DeltaE6) or 16aa (IL-15DeltaE7) both utilizing the normal long signal peptide. Significant structural changes were predicted for these new IL-15 isoforms. RNAse protection assays revealed the highest expression of isoform mRNA in the intestinal epithelium and functional analysis of recombinant IL-15 isoform proteins suggested possible regulatory functions.

Transgenic mouse model of intestine-specific mucosal injury and repair

Most studies of injury and repair to mucosal tissue have used nonspecific mediators to induce injury. Damage to the mucosal epithelium resulting from chemical or radiation treatment associated with cancer therapy may fall into this category of injury. When such treatments are applied, it is generally not possible to predict or control the extent of possible injury. This fact makes analysis of inductive and reparative processes difficult. In addition, the role of the immune system in the etiology and subsequent healing of mucosal tissue following cancer therapy with or without bone marrow transplantation remains unclear. To study tissue- and antigen-specific immune damage of intestinal mucosal tissue, we generated transgenic mice that express a nominal antigen exclusively in intestinal epithelial cells. The transfer of antigen-specific CD8 T cells with concomitant virus infection resulted in the destruction of intestinal epithelial cells and disease. The destructive phase in some cases was followed by complete recovery and tolerance induction. This model will provide a system that can be regulated for analysis of the mediators of mucosa-specific tissue damage and repair.

Preferential localization of effector memory cells in nonlymphoid tissue

Many intracellular pathogens infect a broad range of host tissues, but the importance of T cells for immunity in these sites is unclear because most of our understanding of antimicrobial T cell responses comes from analyses of lymphoid tissue. Here, we show that in response to viral or bacterial infection, antigen-specific CD8 T cells migrated to nonlymphoid tissues and were present as long-lived memory cells. Strikingly, CD8 memory T cells isolated from nonlymphoid tissues exhibited effector levels of lytic activity directly ex vivo, in contrast to their splenic counterparts. These results point to the existence of a population of extralymphoid effector memory T cells poised for immediate response to infection.

Organ-specific regulation of the CD8 T cell response to Listeria monocytogenes infection

The intestinal mucosal CD8 T cell response to infection with Listeria monocytogenes was measured using MHC class I tetramers and was compared with the response in peripheral blood, secondary lymphoid tissue, and liver. To assess the vaccination potential of Listeria and to analyze responses in C57BL/6 mouse strains, a recombinant Listeria expressing OVA (rLM-ova) was generated. The response peaked at 9 days postinfection with a much larger fraction of the intestinal mucosa and liver CD8 T cell pool OVA specific, as compared with the spleen. However, these differences were not linked to bacterial titers in each site. The higher responses in lamina propria and liver resulted in a larger CD8 memory population in these tissues. Furthermore, the level of memory induced was dependent on infectious dose and inversely correlated with the magnitude of the recall response after oral challenge. Recall responses in the tissues were most robust in the lamina propria and liver, and reactivated Ag-specific T cells produced IFN-gamma. Infection of CD40- or MHC class II-deficient mice induced poor CD8 T cell responses in the intestinal mucosa, but only partially reduced responses in the spleen and liver. Overall, the results point to novel pathways of tissue-specific regulation of primary and memory antimicrobial CD8 T cell responses.

Direct analysis of the dynamics of the intestinal mucosa CD8 T cell response to systemic virus infection

The CD8 T cell response to vesicular stomatitis virus infection was characterized in the spleen and intestinal mucosa using MHC tetramers. Surprisingly, the primary response persisted in the lamina propria long after the splenic response had declined. Furthermore, the response was characterized by a protracted effector phase in which cytolytic activity in the lamina propria, but not in the spleen, was maintained. The appearance of Ag-specific cells in the intestinal mucosa was largely, though not exclusively, a result of beta(7) integrin-mediated migration. Infection with Listeria monocytogenes or with vaccinia virus also led to sustained mucosal responses. After reinfection of vesicular stomatitis virus-primed mice with a serotypically distinct virus, a sustained recall response was detected in all tissues. In CD40(-/-) mice, the mucosal, but not the splenic, response was compromised, resulting in diminished mucosal memory. The recall response was CD40 independent and correlated with memory levels, indicating that the mucosal and systemic responses operated independently. These findings illustrated the integrated yet distinct nature of systemic vs mucosal immune responses.

Interleukin-7 mediates the homeostasis of naïve and memory CD8 T cells in vivo

The naïve and memory T lymphocyte pools are maintained through poorly understood homeostatic mechanisms that may include signaling via cytokine receptors. We show that interleukin-7 (IL-7) plays multiple roles in regulating homeostasis of CD8+ T cells. We found that IL-7 was required for homeostatic expansion of naïve CD8+ and CD4+ T cells in lymphopenic hosts and for CD8+ T cell survival in normal hosts. In contrast, IL-7 was not necessary for growth of CD8+ T cells in response to a virus infection but was critical for generating T cell memory. Up-regulation of Bcl-2 in the absence of IL-7 signaling was impaired after activation in vivo. Homeostatic proliferation of memory cells was also partially dependent on IL-7. These results point to IL-7 as a pivotal cytokine in T cell homeostasis.

Establishment and characterization of a spontaneously immortalized myofibroblast cell line derived from a human liver angiosarcoma

BACKGROUND/AIM

Fibrosis and/or cirrhosis are present in the precursor stages of most liver cancers. However, little is known about the reciprocal interactions of fibroblasts, mainly responsible for fibrosis, and the other liver cells. We report here the isolation of a new liver myofibroblast cell line from a human liver angiosarcoma and its characterization.

METHODS

The cells were isolated by the explant technique and characterization was performed, on one hand, using immunohistochemical and ultrastructural analysis and, in the other hand, by determining their karyotype, ras and p53 status and their tumorigenic properties.

RESULTS

To date, the cells have undergone approximately 170 population doublings and are still proliferating. Immunohistochemically, they were negative for desmin, smooth muscle myosin, cytokeratin 19 and von Willebrand factor, positive for vimentin and alpha-smooth muscle actin, with an important deposition of fibronectin around the cells. Ultrastructure showed particularly cytoplasmic microfilament bundles. Their chromosome number ranged from 38 to 168 with a bimodal population, near diploid and hypotetraploid. No mutations were found in codons 12, 13 or 61 of Ha-, Ki- and N-ras genes but a homozygous missense mutation in codon 179 (CAT-->CTT) was detected in the p53 gene. They were unable to form foci in soft agar or tumors in nude mice.

CONCLUSIONS

Taken together, these results show that these cells, called BM 2.2.1, exhibited typical myofibroblast-like features. Although they contained a karyotype suggestive of tumoral cells and a homozygous mutated p53 gene, they were not tumorigenic. The nature of these cells and the abnormalities of the p53 gene and the karyotype, suggest that: i) they were a component of the tumor stroma, and ii) they could have been involved in angiosarcoma development. Thus, this cell line may be valuable for the study of cellular interactions in liver carcinogenesis.

Expression of intestine-specific antigen reveals novel pathways of CD8 T cell tolerance induction

Reactivity to intestinal epithelium-specific antigen was studied by transgenic expression of cytosolic ovalbumin controlled by an enterocyte-specific promoter. Transferred OVA-specific CD8 cells (OT-I) preferentially expanded in mucosal lymphoid tissues and the epithelium but failed to cause tissue damage. In contrast, concomitant VSV-ova infection induced OT-I-mediated epithelial cell destruction that correlated with antigen density. OT-I cells retained in the epithelium exhibited high levels of lytic activity but were unable to produce cytokines. The mice were systemically tolerant to OVA since endogenous CD8 cells were nonresponsive to VSV-ova infection. Thus, intestinal antigen gained access to peripheral tissues via absorption from effete epithelial cells. This system demonstrated a requirement for inflammation to drive pathogenic autoreactivity against enterocytes and identified pathways of intestine-specific immunoregulation.

Ras gene mutations in vinyl chloride-induced liver tumours are carcinogen-specific but vary with cell type and species

Previous studies have shown that a high proportion (5/6) of human liver angiosarcomas (ASL) associated with exposure to vinyl chloride (VC) contains a GC-->AT mutation at the Ki-ras codon 13. This mutation, however, has not been found in 5 ASL or 2 hepatocellular carcinomas (HCC) induced in rats by VC. These 2 HCC did contain a mutation at codon 61 of the Ha-ras gene. In order to extend this study and further explore the mechanisms of tumour induction, an additional 6 ASL and 6 HCC induced in rats by VC were analysed for ras gene point mutations, as well as 10 rat and 10 murine ASL induced by vinyl fluoride (VF), and 5 ASL, 6 Kupffer cell sarcomas, 4 HCC and 2 cholangiocellular carcinomas induced by Thorotrast in rats. Tumour DNA was analysed by PCR-SSCP and direct sequencing. None of the rodent ASL contained a mutation at codon 13 of the Ki-ras gene showing that the ras gene mutational pattern is species-specific. The CAA-->CTA mutation, previously found at codon 61 of the Ha-ras gene in rat HCC, was observed in 5 further VC-induced HCC but was not detected in the Thorotrast-induced HCC, suggesting carcinogen-specificity. This mutation was also absent in VC-induced ASL, which supports the cell-specificity of the ras mutational pattern in chemically induced tumours. No predominant mutation was detected in VF- and Thorotrast-induced tumours. Thus, a given mutation in a tumour may be carcinogen-specific but also depend on the species and the cell type.

Ras gene mutations in vinyl chloride-induced liver tumours are carcinogen-specific but vary with cell type and species

Previous studies have shown that a high proportion (5/6) of human liver angiosarcomas (ASL) associated with exposure to vinyl chloride (VC) contains a GC-->AT mutation at the Ki-ras codon 13. This mutation, however, has not been found in 5 ASL or 2 hepatocellular carcinomas (HCC) induced in rats by VC. These 2 HCC did contain a mutation at codon 61 of the Ha-ras gene. In order to extend this study and further explore the mechanisms of tumour induction, an additional 6 ASL and 6 HCC induced in rats by VC were analysed for ras gene point mutations, as well as 10 rat and 10 murine ASL induced by vinyl fluoride (VF), and 5 ASL, 6 Kupffer cell sarcomas, 4 HCC and 2 cholangiocellular carcinomas induced by Thorotrast in rats. Tumour DNA was analysed by PCR-SSCP and direct sequencing. None of the rodent ASL contained a mutation at codon 13 of the Ki-ras gene showing that the ras gene mutational pattern is species-specific. The CAA-->CTA mutation, previously found at codon 61 of the Ha-ras gene in rat HCC, was observed in 5 further VC-induced HCC but was not detected in the Thorotrast-induced HCC, suggesting carcinogen-specificity. This mutation was also absent in VC-induced ASL, which supports the cell-specificity of the ras mutational pattern in chemically induced tumours. No predominant mutation was detected in VF- and Thorotrast-induced tumours. Thus, a given mutation in a tumour may be carcinogen-specific but also depend on the species and the cell type.

Soluble antigen and CD40 triggering are sufficient to induce primary and memory cytotoxic T cells

The signals directing induction of tolerance rather than immunity are largely unknown. The CD8 T cell response to soluble Ags generally results in deletional tolerance following transient, costimulation-dependent activation. We demonstrated that CD40 signaling reversed the outcome of this response. Adoptive transfer of OVA-specific CD8 T cells followed by soluble OVA immunization resulted in induction of lytic activity and optimal clonal expansion only when CD40 was triggered via an agonistic mAb. Activation of CD8 T cells by CD40 signaling was indirect, because CD40 expression by host cells was required. CD40 signaling along with soluble Ag immunization also induced expansion of secondary lymphoid and intestinal mucosal endogenous OVA-specific CD8 T cells as detected by MHC tetramer reactivity. When CD40 activation was included, long-lived secondary lymphoid and mucosal memory CD8 cells were generated from adoptively transferred and endogenous CD8 T cells. Mucosal and peripheral CD8 memory cells exhibited constitutive Ag-specific lytic activity, with mucosal memory cells being 10-fold more lytic than splenic or lymph node memory cells. These results demonstrated that CD40 signaling during a response to a poorly immunogenic soluble Ag was necessary and sufficient for CTL and memory T cell induction.

A critical role for CD40-CD40 ligand interactions in amplification of the mucosal CD8 T cell response

The role of CD40 ligand (CD40L) in CD8 T cell activation was assessed by tracking antigen-specific T cells in vivo using both adoptive transfer of T cell receptor transgenic T cells and major histocompatibility complex (MHC) class I tetramers. Soluble antigen immunization induced entry of CD8 cells into the intestinal mucosa and cytotoxic T lymphocyte (CTL) differentiation, whereas CD8 cells in secondary lymphoid tissue proliferated but were not cytolytic. Immunization concurrent with CD40L blockade or in the absence of CD40 demonstrated that accumulation of CD8 T cells in the mucosa was CD40L dependent. Furthermore, activation was mediated through CD40L expressed by the CD8 cells, since inhibition by anti-CD40L monoclonal antibodies occurred after adoptive transfer to CD40L-deficient mice. However, mucosal CD8 T cells in normal and CD40(-/-) mice were equivalent killers, indicating that CD40L was not required for CTL differentiation. Appearance of virus-specific mucosal, but not splenic, CD8 cells also relied heavily on CD40-CD40L interactions. The mucosal CTL response of transferred CD8 T cells was MHC class II and interleukin 12 independent. The results established a novel pathway of direct CD40L-mediated CD8 T cell activation.

Induction and visualization of mucosal memory CD8 T cells following systemic virus infection

Whether CD8 T cell memory exists outside secondary lymphoid organs is unclear. Using an adoptive transfer system that enables tracking of OVA-specific CD8 T cells, we explored the antigenic requirements for inducing CD8 T cell memory and identified intestinal mucosa memory cells. Although systemic immunization with soluble OVA induced clonal expansion, memory CD8 cells were not produced. In contrast, infection with virus-encoding OVA induced memory CD8 cells in the periphery and the lamina propria and intraepithelial compartments of the intestinal mucosa. Mucosal memory cells expressed a distinct array of adhesion molecules as compared with secondary lymphoid memory cells, suggesting that there may be separate mucosal and systemic memory pools. Mucosal CD8 memory cells rapidly produced IFN-gamma after Ag stimulation. Reactivation of memory cells by Ag feeding resulted in increased cell size and up-regulation of CD28 and CD11c. CD8 mucosal memory cells exhibited ex vivo lytic activity that was up-regulated dramatically following Ag reencounter in vivo. Interestingly, reactivation of memory cells did not require CD28-mediated costimulation. The ability of the intestinal mucosa to maintain CD8 memory cells provides a potential mechanism for effective mucosal vaccination.

The role of beta7 integrins in CD8 T cell trafficking during an antiviral immune response

The requirement of beta7 integrins for lymphocyte migration was examined during an ongoing immune response in vivo. Transgenic mice (OT-I) expressing an ovalbumin-specific major histocompatibility complex class I-restricted T cell receptor for antigen were rendered deficient in expression of all beta7 integrins or only the alphaEbeta7 integrin. To quantitate the relative use of beta7 integrins in migration in vivo, equal numbers of OT-I and OT-I-beta7(-/-) or OT-I-alphaE-/- lymph node (LN) cells were adoptively transferred to normal mice. Although OT-I-beta7(-/-) LN cells migrated to mesenteric LN and peripheral LN as well as wild-type cells, beta7 integrins were required for naive CD8 T cell and B cell migration to Peyer's patch. After infection with a recombinant virus (vesicular stomatitis virus) encoding ovalbumin, beta7 integrins became critical for migration of activated CD8 T cells to the mesenteric LN and Peyer's patch. Naive CD8 T cells did not enter the lamina propria or the intestinal epithelium, and the majority of migration of activated CD8 T cells to the small and large intestinal mucosa, including the epithelium, was beta7 integrin-mediated. The alphaEbeta7 integrin appeared to play no role in migration during a primary CD8 T cell immune response in vivo. Furthermore, despite dramatic upregulation of alphaEbeta7 by CD8 T cells after entry into the epithelium, long-term retention of intestinal intraepithelial lymphocytes was also alphaEbeta7 independent.

Generation of mucosal cytotoxic T cells against soluble protein by tissue-specific environmental and costimulatory signals

We compared peripheral and mucosal primary CD8 T cell responses to inflammatory and noninflammatory forms of antigen in a T cell-adoptive transfer system. Immunization with the soluble antigen, ovalbumin (ova), administered i.p. or orally without adjuvant, activated nonmucosal CD8 T cells but did not induce cytotoxic activity. However, after activation, the transferred cells entered the intestinal mucosa and became potent antigen-specific killers. Thus, exogenous intact soluble protein entered the major histocompatibility complex class I antigen presentation pathway and induced mucosal cytotoxic T lymphocytes. Moreover, distinct costimulatory requirements for activation of peripheral versus mucosal T cells were noted in that the CD28 ligand, B7-1, was critical for activated mucosal T cell generation but not for activation of peripheral CD8 T cells. The costimulator, B7-2, was required for optimum activation of both populations. Infection with a new recombinant vesicular stomatitis virus encoding ovalbumin induced lytic activity in mucosal as well as peripheral sites, demonstrating an adjuvant effect of inflammatory mediators produced during virus infection. Generation of antiviral cytotoxic T lymphocytes was also costimulation-dependent. The results indicated that induction of peripheral tolerance via antigen administration may not extend to mucosal sites because of distinct costimulatory and inflammatory signals in the mucosa.

The role of IL-7 in thymic and extrathymic development of TCR gamma delta cells

IL-7-deficient (IL-7(-/-)) mice have reduced numbers of B and TCR alpha beta cells, but lack mature TCR gamma delta cells. Although most T cell development occurs in the thymus, some intestinal intraepithelial lymphocytes (IEL), including TCR gamma delta cells, can develop extrathymically. Epithelial cells in both thymus and intestine synthesize IL-7, suggesting that TCR gamma delta cell development could occur in either site. To evaluate the role of thymic IL-7 in development of TCR gamma delta cells, newborn TCR beta-deficient (TCR beta(-/-)) thymi were grafted to IL-7(-/-) mice. Donor- and host-derived TCR gamma delta cells were recovered from thymus grafts, spleen, and IEL. However, when IL-7(-/-) thymi were grafted to TCR beta(-/-) mice, no development of graft-derived TCR gamma delta cells occurred, indicating that extrathymic IL-7 did not support TCR gamma delta IEL generation from newborn thymic precursors. In contrast, TCR gamma delta IEL development occurred efficiently in adult, thymectomized, irradiated C57BL/6J mice reconstituted with IL-7(-/-) bone marrow. This demonstrated that extrathymic development of TCR gamma delta IEL required extrathymic IL-7 production. Thus, intrathymic IL-7 was required for development of thymic TCR gamma delta cells, while peripheral IL-7 was sufficient for development of extrathymic TCR gamma delta IEL.

Glycosyltransferase regulation mediated by pre-TCR signaling in early thymocyte development

CT1 is a carbohydrate moiety of CD45 that is expressed on fetal thymocytes in vivo. Examination of CT1 expression on thymocyte subsets revealed that primarily pro-T cells (CD44+ CD25+) and pre-T cells (CD44- CD25+) expressed CT1. Interestingly, non-T-lineage committed lymphoid progenitors (CD44+ CD25-) lacked CT1 indicating temporal regulation of expression of this determinant in early T-lineage committed development. In addition, CT1 was expressed by the majority of thymocytes in RAG-2(-/-) mice where thymocyte development is blocked at the CD44- CD25+ stage. Since late pre-T cells (CD44- CD25-) lacked the CT1 epitope we tested whether pre-TCR triggering regulated CT1 expression. Injection of CD3epsilon-specific mAb into RAG-2(-/-) mice induces differentiation of immature thymocytes to the double-positive stage of thymocyte development. Using this system, we demonstrated that expression of CT1 by RAG-2(-/-) thymocytes was rapidly lost from pre-T cells following anti-CD3 mAb treatment. Furthermore, the decline in CT1 expression induced by CD3 signaling paralleled a loss of mRNA for the glycosyltransferase responsible for the addition of CT1 to CD45. Flow cytometric analysis also revealed that the loss of the CT1 epitope was inversely correlated with an increase in peanut agglutinin ligand expression, demonstrating a complex regulation of cell surface glycosylation at a critical juncture in thymocyte development.

Activation and migration of CD8 T cells in the intestinal mucosa

The activation of CD8 T cells was studied using transgenic mice expressing an MHC class I-restricted OVA-specific TCR (OT-I). Immunization of OT-I mice resulted in activation of lymph node T cells and up-regulation of expression of B220, CD11a, and CD44 and caused a preferential loss of mucosal-type T cells from the periphery. Immunization induced dramatic changes in intestinal lymphocytes, including the appearance of a CD11a high population that resembled peripheral T cells and induced a primary cytolytic response. Activation of adoptively transferred OT-I cells induced migration of CD8 T cells into the lamina propria and intraepithelial lymphocyte compartments. The results suggest that Ag presentation in the intestinal epithelium occurs, and that CD8 cells activated in the periphery can readily enter the mucosa during an ongoing immune response.

Activation and migration of CD8 T cells in the intestinal mucosa

The activation of CD8 T cells was studied using transgenic mice expressing an MHC class I-restricted OVA-specific TCR (OT-I). Immunization of OT-I mice resulted in activation of lymph node T cells and up-regulation of expression of B220, CD11a, and CD44 and caused a preferential loss of mucosal-type T cells from the periphery. Immunization induced dramatic changes in intestinal lymphocytes, including the appearance of a CD11a high population that resembled peripheral T cells and induced a primary cytolytic response. Activation of adoptively transferred OT-I cells induced migration of CD8 T cells into the lamina propria and intraepithelial lymphocyte compartments. The results suggest that Ag presentation in the intestinal epithelium occurs, and that CD8 cells activated in the periphery can readily enter the mucosa during an ongoing immune response.

Age-dependent intestinal lymphoproliferative disorder due to stem cell factor receptor deficiency: parameters in small and large intestine

Signaling through c-Kit/stem cell factor (SCF) is crucial for normal development of erythroid and myeloid hematopoietic precursors and of melanocytes and germ cells. While peripheral lymphoid populations of W/Wv and SI/SId mice appear normal, we demonstrated that the intraepithelial lymphocyte (IEL) populations of small (SI) and large (LI) intestine were significantly affected. IEL populations of young W/Wv animals were indistinguishable from those of their control littermates, but an age-dependent decrease in SI and LI TCRgamma delta IEL occurred in c-Kit mutant mice. In SI, but not in LI, this diminution was accompanied by gross expansion of TCRalpha beta IEL that resulted in significantly increased IEL:epithelial cell ratios in c-Kit mutant mice. Bromodeoxyuridine labeling studies revealed that the increase in cell numbers was due to lymphoproliferation that occurred in situ. Interestingly, TCRgamma delta IEL expressed cell surface c-Kit, while the expanding population of TCRalpha beta IEL did not. Analysis of radiation bone marrow chimeras demonstrated that the dysregulation required either disruption of stromal cell SCF or IEL c-Kit and showed that the effect on IEL or their precursors was not due to other changes in the intestinal microenvironment. Lamina propria T cell populations in these mice were unaffected, reinforcing the idea that the developmental requirements of these gut-resident lymphocyte populations are distinct. Overall, the results demonstrated that the development of intestinal TCRgamma delta IEL, regardless of location, shares common requirements for SCF, while SI and LI TCRalpha beta IEL may develop along distinct pathways. Possible mechanisms for the loss of proliferative regulation in gut T cells in c-Kit/SCF deficiency are discussed.

Age-dependent intestinal lymphoproliferative disorder due to stem cell factor receptor deficiency: parameters in small and large intestine

Signaling through c-Kit/stem cell factor (SCF) is crucial for normal development of erythroid and myeloid hematopoietic precursors and of melanocytes and germ cells. While peripheral lymphoid populations of W/Wv and SI/SId mice appear normal, we demonstrated that the intraepithelial lymphocyte (IEL) populations of small (SI) and large (LI) intestine were significantly affected. IEL populations of young W/Wv animals were indistinguishable from those of their control littermates, but an age-dependent decrease in SI and LI TCRgamma delta IEL occurred in c-Kit mutant mice. In SI, but not in LI, this diminution was accompanied by gross expansion of TCRalpha beta IEL that resulted in significantly increased IEL:epithelial cell ratios in c-Kit mutant mice. Bromodeoxyuridine labeling studies revealed that the increase in cell numbers was due to lymphoproliferation that occurred in situ. Interestingly, TCRgamma delta IEL expressed cell surface c-Kit, while the expanding population of TCRalpha beta IEL did not. Analysis of radiation bone marrow chimeras demonstrated that the dysregulation required either disruption of stromal cell SCF or IEL c-Kit and showed that the effect on IEL or their precursors was not due to other changes in the intestinal microenvironment. Lamina propria T cell populations in these mice were unaffected, reinforcing the idea that the developmental requirements of these gut-resident lymphocyte populations are distinct. Overall, the results demonstrated that the development of intestinal TCRgamma delta IEL, regardless of location, shares common requirements for SCF, while SI and LI TCRalpha beta IEL may develop along distinct pathways. Possible mechanisms for the loss of proliferative regulation in gut T cells in c-Kit/SCF deficiency are discussed.

Beta2 integrins and ICAM-1 are involved in establishment of the intestinal mucosal T cell compartment

Development of the mucosal immune system was examined in mice with partial loss of expression of ICAM-1 or CD18. Profound effects on Peyer's patch (PP), lamina propria (LP), and intraepithelial lymphocyte (IEL) T cell populations were observed in mutant mice. Normal expression of CD18 integrins and ICAM-1 was essential for development of the CD8(alpha beta) TCR(alpha beta)LP and IEL compartment and for the generation of normal PP lymphocyte populations. The partial loss of CD8(alpha beta) IEL correlated with the loss of TCR(alpha beta) IEL-mediated lytic activity. The presence of a subset of Thy1+TCR(gamma delta)IEL was also dependent on CD18 integrins and ICAM-1. Both the lytic activity and the expression of CD11c by TCR(gamma delta)IEL were up-regulated in the presence of TCR(alpha beta) T cells. Analysis of bone marrow chimeras demonstrated that a bone marrow-derived ICAM-1+ accessory cell was involved in the generation of some TCR(alpha beta) IEL. These results demonstrated that ICAM-1 and beta2 integrins were required for establishment of a normal intestinal immune system.

Requirement for extrathymic class I histocompatibility antigens for positive selection of thymus-derived T lymphocytes

We have examined whether the thymus can produce immature T cell precursors for subsequent positive selection in the periphery. Using the intestine as a model system, we demonstrate that extrathymic MHC class I molecules positively select thymus-derived TCR-alpha beta CD8+ intestinal intraepithelial lymphocytes. Grafting of MHC class I+ thymus onto MHC class I- hosts resulted in the generation of donor and host-derived CD4-CD8+ T cells in lymph node, but few TCR-alpha beta CD4-CD8+ intraepithelial lymphocytes. The results indicate that the intestine can act as a site of positive selection for thymus-derived T cells. Bone marrow reconstitution studies demonstrated that non-hematopoietic, radiation-resistant cells, perhaps intestinal epithelial cells, were responsible for extrathymic positive selection of thymus-derived T cells. These findings demonstrate that the thymus can support organ-specific immunity via provision of targeted precursor populations.

Requirement for extrathymic class I histocompatibility antigens for positive selection of thymus-derived T lymphocytes

We have examined whether the thymus can produce immature T cell precursors for subsequent positive selection in the periphery. Using the intestine as a model system, we demonstrate that extrathymic MHC class I molecules positively select thymus-derived TCR-alpha beta CD8+ intestinal intraepithelial lymphocytes. Grafting of MHC class I+ thymus onto MHC class I- hosts resulted in the generation of donor and host-derived CD4-CD8+ T cells in lymph node, but few TCR-alpha beta CD4-CD8+ intraepithelial lymphocytes. The results indicate that the intestine can act as a site of positive selection for thymus-derived T cells. Bone marrow reconstitution studies demonstrated that non-hematopoietic, radiation-resistant cells, perhaps intestinal epithelial cells, were responsible for extrathymic positive selection of thymus-derived T cells. These findings demonstrate that the thymus can support organ-specific immunity via provision of targeted precursor populations.

Antigen-driven induction of CD11c on intestinal intraepithelial lymphocytes and CD8+ T cells in vivo

Intraepithelial lymphocytes (IEL) of the intestinal epithelium represent a phenotypically and functionally distinct subpopulation of peripheral T cells. In this study, we report the production of a mAb, designated HL3, which exhibits reactivity with a subset of IEL. In differential screening assays HL3 reacted with 30 to 50% of IEL, but not with T cells of the thymus, spleen, or lymph nodes. Biochemical characterization revealed that the HL3 mAb recognized p150,95 (CD11c/CD18; CR4), a member of the beta 2-integrin family. Fluorescence flow cytometric analyses showed that p150,95 was expressed by TCR-alpha beta or TCR-gamma delta CD4-8+ IEL but not by CD4+8- IEL. Induction of graft-vs-host (GVH) disease resulted in up-regulation of p150,95 expression on donor-derived CD8+ T cells in the intestinal epithelium, as well as in the spleen and lymph nodes. GVH also induced MAC-1 (CD11b) expression on a subset of CD8+ lymph node T cells, but MAC-1 was not up-regulated on CD8+ IEL in this situation. In contrast, activation of identical T cell responders in vitro resulted in weak induction of p150,95 and MAC-1 expression. This result suggested that activation alone was insufficient for p150,95 up-regulation and that additional factors available in vivo were essential in this process. In the intestine, induction of p150,95 required the presence of intestinal flora as IEL from germfree mice lacked p150,95. Interestingly, gamma delta IEL expressing a non-IEL type transgenic TCR were also p150,95-, but exposure to Ag in vivo, but not in vitro, resulted in p150,95 induction. This result indicated that the constitutive expression of p150,95 on IEL is likely due to Ag stimulation via the TCR and not a bystander phenomenon. Overall, the results demonstrated p150,95 to be a hallmark of T cell activation in vivo and an indicator of ongoing antigen-specific T cell activation in the intestinal epithelium.

Antigen-driven induction of CD11c on intestinal intraepithelial lymphocytes and CD8+ T cells in vivo

Intraepithelial lymphocytes (IEL) of the intestinal epithelium represent a phenotypically and functionally distinct subpopulation of peripheral T cells. In this study, we report the production of a mAb, designated HL3, which exhibits reactivity with a subset of IEL. In differential screening assays HL3 reacted with 30 to 50% of IEL, but not with T cells of the thymus, spleen, or lymph nodes. Biochemical characterization revealed that the HL3 mAb recognized p150,95 (CD11c/CD18; CR4), a member of the beta 2-integrin family. Fluorescence flow cytometric analyses showed that p150,95 was expressed by TCR-alpha beta or TCR-gamma delta CD4-8+ IEL but not by CD4+8- IEL. Induction of graft-vs-host (GVH) disease resulted in up-regulation of p150,95 expression on donor-derived CD8+ T cells in the intestinal epithelium, as well as in the spleen and lymph nodes. GVH also induced MAC-1 (CD11b) expression on a subset of CD8+ lymph node T cells, but MAC-1 was not up-regulated on CD8+ IEL in this situation. In contrast, activation of identical T cell responders in vitro resulted in weak induction of p150,95 and MAC-1 expression. This result suggested that activation alone was insufficient for p150,95 up-regulation and that additional factors available in vivo were essential in this process. In the intestine, induction of p150,95 required the presence of intestinal flora as IEL from germfree mice lacked p150,95. Interestingly, gamma delta IEL expressing a non-IEL type transgenic TCR were also p150,95-, but exposure to Ag in vivo, but not in vitro, resulted in p150,95 induction. This result indicated that the constitutive expression of p150,95 on IEL is likely due to Ag stimulation via the TCR and not a bystander phenomenon. Overall, the results demonstrated p150,95 to be a hallmark of T cell activation in vivo and an indicator of ongoing antigen-specific T cell activation in the intestinal epithelium.

Effects of aging on pituitary growth hormone-releasing factor receptor binding sites: in vitro mimicry by guanyl nucleotides and reducing agents

We have investigated the effect of 5'-guanylylimidodiphosphate (Gpp(NH)p) and two disulfide bond reducing agents, reduced glutathione (GSH) and dithiothreitol (DTT), on the modulation of [125I-Tyr10]hGRF(1-44)NH2 binding to GRF receptor binding sites, in pituitaries of young and aging rats. In pituitaries from 2-month-old rats, Gpp(NH)p (0.1-1.0 mM), GSH and DTT (1-50 mM) exhibited a partial but concentration-dependent inhibitory effect on GRF specific binding. These effects were associated with a conversion of the high affinity GRF binding sites to lower affinity sites and to a reduction of the apparent number of total binding sites (high and low). No potentiation of these effects was observed when Gpp(NH)p (1 mM) and DTT (1 mM) were combined. In pituitaries from 14-month-old rats, Gpp(NH)p (1 mM) was capable of modulating GRF binding parameters in a similar fashion to that in pituitaries from 2-month-old rats. In pituitaries from 18-month-old rats, the high affinity GRF binding sites were already blunted and neither Gpp(NH)p nor Gpp(NH)p plus DTT significantly altered GRF binding parameters. In addition, in 20-month-old rats, the affinity of hGRF(1-29)NH2 and that of the full antagonist N alpha-Ac-[D-Arg2,Ala15]rGRF(1-29)NH2 were respectively decreased 9.3- and 9.9-fold. Our results suggest that in aging, alterations of GRF receptor binding sites could involve disulfide bond reduction or other structural modifications leading to conformational changes, similar to those induced by GSH or DTT. Such structural changes may prevent an efficient coupling of the GRF receptor with its ligands and G-protein, leading to a loss of somatotroph responsiveness.

Extrathymic intestinal T-cell development: virtual reality?

Extrathymic T-cell development is a topic of considerable interest and debate, with important implications for the mechanisms of T-cell maturation and repertoire selection. Recent evidence has suggested that intraepithelial T lymphocytes (IELs) of the small intestine can mature and undergo selection in the absence of a thymus. However, IEL precursors are present in the thymus and IEL development is known to be influenced by the thymus. Here, Leo Lefrançois and Lynn Puddington discuss these data and suggest that the differentiation pathway of IEL precursors is dependent on whether or not a thymus is present.

Interactions between stem cell factor and c-Kit are required for intestinal immune system homeostasis

Interactions between stem cell factor (SCF) and its receptor, c-Kit, are important for development of hematopoietic, melanocytes, and germ cells. T lymphocytes appeared normal in c-Kit (W/Wv) or SCF (SI/SId) mutant mice, except for those residing within the intestinal epithelium, the intraepithelial lymphocytes (IEL). Normally, IEL are composed of equal numbers of cells with alpha beta or gamma delta T cell receptors. In mutant mice, beginning at 6-8 weeks of age, the number of gamma delta IEL decreased, whereas alpha beta IEL increased. The latter was due largely to an increased CD4+ CD8+ TCR alpha beta subset, suggesting that these cells may be intermediates in the alpha beta IEL lineage. c-Kit or SCF was expressed by IEL or intestinal epithelial cells, respectively, indicating a potential for direct intercellular interaction. This possibility was supported by reconstitution studies that demonstrated that c-Kit mutations directly affected IEL. Thus, SCF-c-Kit interactions are important for homeostasis of the intestinal immune compartment.

A novel pathway of thymus-directed T lymphocyte maturation

Recent evidence has indicated that the intestinal epithelium may be a major extrathymic site of T cell production. However, which of the multiple intestinal intraepithelial lymphocyte (IEL) subsets are extrathymic in origin has been controversial. We now report that the thymus is an integral component of IEL maturation and is required for a novel two-stage process of T cell production. Thus, in neonatally thymectomized mice TCR-gamma delta IELs were depleted and some TCR-alpha beta IELs were of an immature phenotype. Thymus grafting experiments revealed that all TCR-gamma delta and TCR-alpha beta IEL subsets could be thymus-derived, including TCR-alpha beta cells lacking Thy1 and CD8 beta. In utero anti-TCR-gamma delta mAb treatments resulted in depletion of gamma delta IEL without subsequent re-emergence of this subset in adulthood, whereas anti-TCR-alpha beta mAb treatment only marginally reduced the alpha beta IEL subset. These findings suggest that TCR-alpha beta and TCR-gamma delta IELs arose at distinct developmental stages. Overall, the results indicate that some IEL precursors are thymus-derived but require further thymic influence to mature in the periphery.

A novel pathway of thymus-directed T lymphocyte maturation

Recent evidence has indicated that the intestinal epithelium may be a major extrathymic site of T cell production. However, which of the multiple intestinal intraepithelial lymphocyte (IEL) subsets are extrathymic in origin has been controversial. We now report that the thymus is an integral component of IEL maturation and is required for a novel two-stage process of T cell production. Thus, in neonatally thymectomized mice TCR-gamma delta IELs were depleted and some TCR-alpha beta IELs were of an immature phenotype. Thymus grafting experiments revealed that all TCR-gamma delta and TCR-alpha beta IEL subsets could be thymus-derived, including TCR-alpha beta cells lacking Thy1 and CD8 beta. In utero anti-TCR-gamma delta mAb treatments resulted in depletion of gamma delta IEL without subsequent re-emergence of this subset in adulthood, whereas anti-TCR-alpha beta mAb treatment only marginally reduced the alpha beta IEL subset. These findings suggest that TCR-alpha beta and TCR-gamma delta IELs arose at distinct developmental stages. Overall, the results indicate that some IEL precursors are thymus-derived but require further thymic influence to mature in the periphery.

Identification of receptor-binding pharmacophores of growth-hormone-releasing factor in rat adenopituitary

Previous structure-activity studies on growth-hormone-releasing factor (GRF) have mainly been carried out in pituitary cell culture assays. In such systems, the molecular features necessary to increase GRF receptor affinity cannot be fully distinguished from those that improve proteolytic resistance. To assess the affinity of GRF analogues, we have recently characterized [125I-Tyr10]hGRF(1-44)NH2 binding to rat adenopituitary, developing a reliable binding assay in which GRF-carboxamide-related peptides are stable. In the present study, we have determined the binding affinity of two series of analogues in which the entire sequence of hGRF(1-29)NH2 was scanned with D-amino acid and alanine substitutions. To further document their potency, we have evaluated the ability of representative candidates of each series to stimulate cAMP production. In the first series, a D-amino acid substitution at Ala4, Ile5, Phe6, Thr7, Val13, Gln16, Leu17, Ala19, Arg20 and Ile26 decreased drastically the binding affinity of hGRF(1-29)NH2 while it induced a smaller decrease at Tyr1, Asp3, Ser9, Tyr10, Arg11, Lys12, Leu14, Ala15, Ser18, Lys21, Leu22, Leu23, Gln24, Met27 and Ser28. Interestingly, a D-substitution in position 8 generated an analogue exhibiting a significantly greater binding affinity than hGRF(1-29)NH2, while it had no influence on hGRF(1-29)NH2 affinity at Ala2, Asp25 and Arg29. Adenylate cyclase activities of [D-Tyr1], [D-Tyr10] and [D-Arg20]hGRF(1-29)NH2 correlate with their binding affinity. In the second series, the largest decrease of binding affinity was observed with an alanine substitution at Tyr1, Asp3, Ile5, Phe6, Tyr10, Arg11, Lys12, Leu14, Leu17, Arg20 and Lys21.(ABSTRACT TRUNCATED AT 250 WORDS)

Developmental expression of the alpha IEL beta 7 integrin on T cell receptor gamma delta and T cell receptor alpha beta T cells

A novel monoclonal antibody, 2E7, was shown by immunoprecipitation to be reactive with the alpha IEL beta 7 integrin and was employed to analyze the expression of this integrin in lymphocyte subsets and during T cell ontogeny. In adult lymph nodes, alpha IEL was expressed at low levels by 40-70% of CD8+ T cells and < 5% of CD4+ T cells. However, virtually all intestinal intraepithelial lymphocytes and approximately 20% of lamina propria CD4+ T cells were 2E7+, indicating a preferential expression of this integrin on mucosal T cells. Examination of alpha IEL integrin expression during thymus ontogeny revealed that approximately 3-5% of fetal or adult thymocytes were 2E7+. Interestingly, early in fetal thymus ontogeny, approximately 40% of 2E7+ cells expressed T cell receptor (TcR)-gamma delta and this subset persisted through birth. A developmental switch occurred such that 2E7+ TcR- CD4-8+ cells detected on fetal day 19 were followed by 2E7+ TcR-alpha beta CD4-8+ cells in the neonatal thymus. The latter population persisted throughout thymus ontogeny into adulthood. Interestingly, a subset of TcR-gamma delta V gamma 3+ day 16 fetal thymocyte dendritic epidermal cell (DEC) precursors were 2E7+, but all mature DEC expressed high levels of alpha IEL integrin, suggesting that the alpha IEL integrin was acquired late in DEC maturation. This possibility was strengthened by immunohistochemical localization of the majority of 2E7+ gamma delta and alpha beta T cells to the medullary regions of the thymus. Overall, the results demonstrate a developmentally ordered expression pattern of the alpha IEL beta 7 integrin that suggests a common function for this integrin during TcR-gamma delta and -alpha beta CD4-8+ T cell thymocyte development or perhaps in effector functions for these subsets.

Basal and stimulated cyclic adenosine 3',5'-monophosphate production in rat adenopituitary homogenates: direct determination by high-performance liquid chromatography

A sensitive and reliable procedure to quantify cAMP in biological samples, without involving radioisotopes, is described. After incubation, the assay mixture was boiled for 4 min, centrifuged, filtered and directly injected onto a mu Bondapak C18 column (10 microns particle size; 150 mm x 3.9 mm I.D.). cAMP was resolved within 40 min in isocratic mode using a mobile phase composed of 96% of 0.01 M ammonium acetate, pH 6.6 and 4% of acetonitrile-water &70:30, v/v) at a flow-rate of 0.5 ml/min. Detection was monitored at 254 nm and quantification was achieved by peak surface integration. The lowest detection limit was 1.6 pmol (signal-to-noise ratio = 2.5). The potential of this assay to perform structure-activity of bioactive peptides is illustrated with growth hormone-releasing factor in rat adenopituitary homogenates.

Proteolytic degradation of rat growth hormone-releasing factor(1-29) amide in rat pituitary and hypothalamus

The identification of peptide bonds vulnerable to tissue peptidases is a valuable approach to design peptide agonists which exhibit a longer duration of action than the native molecules. Therefore, the kinetic of disappearance of rat growth hormone-releasing factor (rGRF(1-29)NH2) and the identification of its metabolites were studied in rat pituitary and hypothalamus. Synthetic rGRF(1-29)NH2 (10 microM) was incubated (0-120 min, 37 degrees C) in the presence of a pituitary (237 +/- 51 micrograms protein/ml) or hypothalamus homogenate (576 +/- 27 micrograms protein/ml). Using analytical high pressure liquid chromatography (HPLC), apparent half-lives of 22 +/- 3 min and 25 +/- 4 min were found in pituitary and hypothalamus, respectively. In both tissues, three degradation products, all less hydrophobic than the native peptide, were detected and isolated by preparative HPLC. The identification of the purified metabolites was ascertained by amino acid analysis, sequencing and chromatography with synthetic homologs. These results indicate that the main sites of cleavage in the pituitary and hypothalamus are Lys21-Leu22 (trypsin-like cleavage site), Leu14-Gly15 and Tyr10-Arg11 (chymotrypsin-like cleavage sites). TLCK and leupeptin did not affect the formation of fragment (1-21)OH while TPCK blocked the cleavage of Leu14-Gly15. The low affinity of fragment (1-21)NH2 for pituitary GRF binding sites suggests that hydrolysis of the Lys21-Leu22 bond inactivates rGRF(1-29)NH2 in this target tissue.

Selection of intestinal intraepithelial lymphocyte T cell receptors: evidence for a dynamic tissue-specific process

An extensive comparison of TCR alpha beta V-region usage by CD8 beta-CD4+CD8+ intraepithelial lymphocytes (IEL), CD4-CD8+ IEL, and lymph node (LN) T cell subsets in three minor lymphocyte stimulating (Mls)-disparate, MHC-identical mouse strains revealed novel TCR selection patterns. In cases where forbidden V regions were expressed by CD8 beta- CD4-CD8+ IEL, the same TCRs were deleted from CD8 beta- CD4+CD8+ IEL, indicating that lack of CD8 beta expression was not solely responsible for forbidden V-region expression. These results also suggested that CD4 may be involved in negative selection of CD4+CD8+ IEL TCRs. In C57BR/cdJ (Mls-1b2b) mice, a major increase in V beta 3+CD4+CD8+ IEL but not in other IEL or LN subsets was noted suggesting a subset-specific expansion of V beta 3+ cells. Negative selection of V beta 14+ cells in only the CD4+CD8+ IEL subset further supported the existence of intestine-specific TCR selection processes. Analysis of V-region expression of CD8 beta + and CD8 beta-CD4-CD8+ IEL subsets revealed that forbidden V-region expression was not strictly confined to the CD8 beta- subset in all cases. Overall, the data point to a dynamic, gut-specific TCR selection process that may be antigen driven.

T cell receptor-triggered activation of intraepithelial lymphocytes in vitro

Intraepithelial lymphocytes (IEL) of the mouse small intestine were examined for their potential to respond to TCR signalling in vitro. Purified IEL subsets were activated using mAbs specific for CD3, TCR alpha beta or TCR gamma delta. Thy-1+ IEL, regardless of TCR type, proliferated equally well in response to anti-TCR mAb with or without exogenous IL-2. In contrast, Thy-1- TCR alpha beta, CD8 beta- IEL required exogenous IL-2 for proliferation. No such requirement was observed for Thy-1- TCR gamma delta IEL proliferation. IEL proliferation in the absence of added IL-2 was due to an IL-2 secretion/IL-2 receptor (IL-2R) autocrine pathway, since mAbs specific for IL-2 and IL-2R inhibited IEL proliferation. Thy-1+ CD8 beta- CD4+CD8+ IEL were unresponsive to TCR-induced proliferation but exhibited high levels of cytolytic activity upon TCR-triggering. Thy-1- non-cytolytic IEL were induced to express Thy-1 and cytolytic activity following activation in vitro. In addition, the involvement of the co-stimulatory molecule CD28 in IEL activation was tested. CD28 was weakly expressed by fresh IEL and anti-CD28 mAb had no effect on TCR-triggered proliferation. However, anti-TCR stimulation increased CD28 expression on a subset of TCR alpha beta IEL and the addition of anti-CD28 mAb resulted in increased IL-2 production, but not in increased proliferation. Our results indicate that IEL, including the purported extrathymic CD8 beta- subset, can respond to TCR-driven signals via proliferation and/or cytolytic activity.

Extrathymic differentiation of intraepithelial lymphocytes: generation of a separate and unequal T-cell repertoire?

A significant number of intraepithelial intestinal T cells appear to mature extrathymically. In this paper, Leo Lefrançois discusses the implication of this for T-cell receptor selection and repertoire generation. He goes on to develop the concept that such cells may constitute discrete subsets of organ-specific lymphocytes, with unique T-cell receptor repertoires that may be evolutionary antecedents of thymus-derived T cells.

Intraepithelial lymphocytes of the intestinal mucosa: curiouser and curiouser

Intraepithelial lymphocytes (IEL) of the intestine are discussed in light of recent findings concerning their ontogeny and T cell receptor expression. IEL are distinct from other peripheral T cells in many aspects, including their homing abilities and their phenotypic characteristics. IEL that express the gamma/delta T cell receptor are singular in that the thymus is not required for their maturation or for the selection of certain T cell receptor variable regions. Despite recent efforts, the in vivo function of IEL with gamma/delta T cell receptors remains unclear. Overall, IEL and the associated mucosa represent a complex lymphoid organ that will be the object of much future experimentation.

Fibrositis and primary hypothyroidism

The prevalence of fibrositis was determined in 100 patients with subclinical or biochemical primary hypothyroidism. Nineteen patients reported symptoms of joint and/or muscle pain with stiffness. Five of these patients presented 7 or more tender points on examination, thus allowing a diagnosis of fibrositis to be made in only 5% of the total group. Symptomatic improvement after thyroid hormone replacement occurred in 10 of the 19 patients, including 3 of those with fibrositis. There were no significant changes in tender points. Our data indicate that fibrositis is uncommon in patients with primary hypothyroidism despite the frequent occurrence of symptoms suggestive of this syndrome.

N protein is the predominant antigen recognized by vesicular stomatitis virus-specific cytotoxic T cells

The specificity of anti-vesicular stomatitis virus (VSV)-specific cytotoxic T cells was explored with cell lines expressing VSV genes introduced by electroporation. Low levels of nucleocapsid (N) protein were detected on the surface of VSV-infected cells, but N protein could not be detected on the plasma membrane of transfected EL4 cells. Intracellular N protein was detectable by enzyme-linked immunosorbent assay or immunoprecipitation in some of the transfected cell lines but not in others, unless the transfected genes were induced by sodium butyrate. However, all of the stably transfected EL4 cell lines expressing the VSV-Indiana N protein were efficiently lysed by serotype-specific and cross-reactive anti-VSV cytotoxic T cells (CTLs). Primary cross-reactive anti-VSV CTLs appeared to be specific solely for N protein, based on cold-target competition assays using infected and transfected target cells. Cell lines expressing 100- to 1,000-fold less N protein than did VSV-infected cells were efficiently lysed by both primary and secondary anti-VSV CTLs. Cell lines expressing 100-fold less G protein than did VSV-infected cells were not lysed by either population of effectors. Significantly, cold-target competition studies with secondary CTLs demonstrated that N protein-expressing cell lines were more efficient competitors than were VSV-infected cells even though the latter expressed 100- to 1,000-fold more N protein. This was not an artifact of viral infection since infection of the transfected cell lines did not affect their ability to compete. The possibility that cell lines constitutively expressing internal virus proteins present antigen more effectively than infected cells do is discussed.