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.