Suppression of murine leukemia virus-mediated 3Y1 cell fusion by expression of mouse MHC class I

Rat 3Y1 fibroblasts transformed by adenovirus type 12 or its E1A gene formed syncytia by cocultivation with Friend murine leukemia virus (MuLV)-producing cells. On the other hand, parental 3Y1 cells and those derivatives induced by other tumor viruses or chemical carcinogen showed no MuLV-mediated syncytium formation [N. Momozaki et al. (1990) Arch. Virol. 115: 123-126]. The expression of major histocompatibility complex (MHC) class I mRNA and antigens was significantly reduced in these Ad12- and E1A-transformed 3Y1 cells. In contrast, other tumor virus-and chemical carcinogen-transformed 3Y1 cells expressed MHC class I almost in normal levels as did parental 3Y1 cells. Furthermore, Ad12-transformed 3Y1 cells which started to express the transfected exogenous MHC class I gene, H-2Ld, showed no more MuLV-mediated 3Y1 cell fusion. These results indicate that the expression of MHC class I on the cell membrane is closely related to the inhibition of 3Y1 cell fusion by MuLV.

Production and effect of infectious Dane particles in transgenic mice

We have demonstrated by immunoelectron microscopy that 42-nm particles with double-shelled structures characteristic of Dane particles are present in the serum of transgenic mice, 1.2HB-BS 10, carrying partly duplicated hepatitis B virus (HBV) genome. Furthermore, these particles were shown to infect primary human fetal hepatocytes as demonstrated by the elevation of HBV surface antigen (HBsAg) in the culture medium. HBV DNA is known to be expressed in a liver- and kidney-specific manner in the adult mouse, so we examined the developmental expression of viral antigens. In the liver, viral antigens (HBsAg and HBV e antigen) began to be expressed before birth and the level of expression showed a sharp rise after birth. On the other hand, in the kidney, viral antigens began to be expressed after birth. Serum levels of viral antigens were roughly proportional to the levels of expression in the liver, suggesting that the liver is the main source for viral antigens in the serum. None of these transgenic mice produced anti-HBs or anti-HBV core response or showed biochemical or pathological change up to at least 24 months of age. All these results suggest that infectious viral particles can be produced in transgenic mice, and that expression and replication of HBV DNA are not toxic in vivo.

Differentiation of growth signal requirement of B lymphocyte precursor is directed by expression of immunoglobulin

During B cell differentiation, at least three stages can be defined in terms of their growth signal requirement by using two different growth signals, which are recombinant interleukin 7 (IL-7) and a stromal cell clone PA6 which does not produce IL-7; first a PA6 dependent stage, second a PA6 + IL-7 dependent stage and third an IL-7 dependent stage. In order to test the possibility that this differentiation of growth signal requirement is controlled by the expression of functional immunoglobulin molecules, we have investigated the frequencies of PA6 + IL-7 dependent and IL-7 dependent cells which are present in the bone marrow of either mu-chain or kappa-chain gene transgenic mice. In a mu-chain gene transgenic mouse, the frequency of PA6 + IL-7 dependent cells is selectively reduced, while that of IL-7 dependent cells is selectively reduced in a kappa-chain gene transgenic mouse. This result suggests that expression of a functional mu-chain gene drives PA6 + IL-7 dependent cells to differentiate into the subsequent IL-7 dependent stage. Likewise, when mu-chain positive IL-7 dependent cells express a functional light-chain gene, their growth signal requirement changes into an IL-7 unreactive stage.

Correlation of tissue-specific methylation with gene inactivity in hepatitis B virus transgenic mice

We produced transgenic mice using two constructs, HB-GII and 1.2HB-BS, of hepatitis B virus (HBV) DNA. The former has been designed to express mRNAs for HBV surface antigen (HBsAg), and the later to express all mRNAs of HBV. Several lines of the transgenic mice carrying each construct were examined for the tissue-specificity and level of HBV DNA expression, and for the relationship between expression and methylation of the transgenes. Only one out of ten for HB-GII and one out of eight for 1.2HB-BS were high producers of viral antigens. In high producers, transgenes were expressed in the liver and the kidneys. But in low producers, transgenes were usually expressed only in the kidneys. There is a reciprocal relationship between the level of expression and the degree of methylation, that is, the higher the level of expression, the less the degree of methylation. We also observed that the expression of the integrated HBV-DNA was repressed by methylation following its passage through the female germline in one line. Thus, in addition to transacting factors that can control the gene expression positively or negatively, this tissue-specific methylation may also be involved in the regulation of HBV gene expression.

HBV production in transgenic mice

We produced transgenic mice by microinjecting a partially duplicated copies of hepatitis B virus (HBV) gene into fertilized eggs of C57BL/6 mice. One mouse was a high producer of HBV surface antigen (HBsAg) and HBV e antigen (HBeAg) in the serum. All offspring carrying HBV DNA were positive for both antigens in the serum. The HBV DNA was expressed in liver- and kidney-specific manner. The normal process of HBV replication, including the packaging of the pregenome 3.5-kb RNA into a nucleocapsid, the reverse-transcription of the complete minus strand DNA, and the release of Dane particles into the serum before the completion of synthesis of plus strand, occurred in the liver of these transgenic mice. These results suggest that the species specificity of HBV infection is not due to the inability to replicate in nonnatural host but to the lack of receptors or factors needed for virus adsorption and internalization. The founder mouse is now 19 months of age but shows no clinical or pathological change, suggesting that HBV itself is not cytopathic.

Tissue-specific expression of rat pyruvate kinase L/chloramphenicol acetyltransferase fusion gene in transgenic mice and its regulation by diet and insulin

We produced transgenic mice carrying about 3 kb of the 5'-flanking sequence of the rat pyruvate kinase L gene linked to the chloramphenicol acetyltransferase (CAT) structural gene. Expression of the transgene was observed only in tissues in which the endogenous L-type pyruvate kinase is expressed. Dietary glucose or insulin induced similar increases in the levels of CAT and L-type pyruvate kinase mRNAs in the liver. However, the fructose-induced level of CAT mRNA was about 3- and 6- fold lower than those of endogenous L-type pyruvate kinase mRNA in the liver and kidney, respectively, confirming our previous finding that stabilization of the transcripts of the pyruvate kinase L gene is an important regulatory step in fructose induction, especially in the kidney. Thus we conclude that all the cis-acting elements responsible for tissue-specific expression of the L-type pyruvate kinase and its stimulation by dietary components and insulin are localized in the sequence from about nucleotide -3000 to +37 in the pyruvate kinase L gene.

Tissue specificity of tropomyosin from the crayfish, Cambarus clarki

The molecular heterogeneity and tissue specificity of crustacean tropomyosin were investigated, using muscle and nonmuscle tissues from the crayfish, Cambarus clarki. In muscle, three types of tropomyosin isoforms were found on two-dimensional gel electrophoresis. One of them was specific to cardiac muscle, and the other two were shared by skeletal and visceral muscles. In nonmuscle tissues, four types of isoforms were found on two-dimensional gel electrophoresis and in immunoreplica tests using an antiserum against crayfish skeletal muscle tropomyosin. Two of them were common to the muscle isoforms, but the other two were not detected in muscles. Furthermore, nonmuscle tissues contained several peculiar isoforms, the electrophoretic mobilities of which were considerably higher than those of the other isoforms mentioned above. When tropomyosin was purified from the mid-gut gland, these isoforms with high mobilities were found in the crude tropomyosin preparation. These results showed that the crayfish tropomyosin was heterogeneous and that the isoforms were distributed in a tissue-specific manner, like vertebrate tropomyosin. However, the results did not coincide with those of our previous study on horseshoe crab tropomyosin, which showed molecular heterogeneity but no tissue specificity. In view of the difference in the isoform distributions between the two major groups (Crustacea and Merostomata) of Arthropoda, the significance of the tissue specificity of tropomyosin isoforms was discussed.

Establishment of a pancreatic beta cell line that retains glucose-inducible insulin secretion: special reference to expression of glucose transporter isoforms

Two cell lines have been established from insulinomas obtained by targeted expression of the simian virus 40 T antigen gene in transgenic mice. These cell lines, designated MIN6 and MIN7, produce insulin and T antigen and have morphological characteristics of pancreatic beta cells. MIN6 cells exhibit glucose-inducible insulin secretion comparable with cultured normal mouse islet cells, whereas MIN7 cells do not. Both cell lines produce liver-type glucose transporter (GT) mRNA at high level. Brain-type GT mRNA is also present at considerable level in MIN7 cells, but is barely detectable in MIN6 cells, suggesting that exclusive expression of the liver-type GT is related to glucose-inducible insulin secretion. MIN6 cells do not express either major histocompatibility (MHC) class I or class II antigens on the cell surface. However, treatment with interferon-gamma induces high levels of MHC class I antigens, and a combination of interferon-gamma and tumor necrosis factor-alpha induces a MHC class II antigen on the cell surface. These results emphasize that the MIN6 cell line retains physiological characteristics of normal beta cells. The MIN6 cell line will be especially useful to analyze the molecular mechanisms by which beta cells regulate insulin secretion in response to extracellular glucose concentrations. We discuss a possible role of GT isoforms in glucose sensing by beta cells.

Direct evidence for the contribution of the unique I-ANOD to the development of insulitis in non-obese diabetic mice

Insulin-dependent diabetes mellitus is characterized by the infiltration of lymphocytes into the islets of Langerhans of the pancreas (insulitis) followed by destruction of insulin-secreting beta-cells leading to overt diabetes. The best model for the disease is the non-obese diabetic (NOD) mouse. Two unusual features of the class II major histocompatibility complex (MHC) of the NOD mouse are the absence of I-E and the presence of unique I-A molecules (I-ANOD), in which aspartic acid at position 57 of the beta-chain is replaced by serine. This feature is also found in the HLA-DQ chain of many Caucasians with insulin-dependent diabetes mellitus. We have previously reported that the expression of I-E prevents the development of insulitis in NOD mouse. Here we report that the expression of I-Ak (A alpha kA beta k) in transgenic NOD mice can also prevent insulitis, and that this protection is seen not only when the I-A beta-chain has aspartic acid as residue 57, but also when this residue is serine. These results show that the single amino-acid substitution at position 57 of the I-A beta-chain from aspartic acid to serine is not sufficient for the development of the disease.

Accumulation of tropomyosin in developing chicken gizzard smooth muscle

Smooth muscle of chicken embryonic gizzards has been shown to contain 9 tropomyosin isoforms (E1, E2, E3, E4, E5, E6, E7, E8, and E9) in addition to alpha and beta isoforms (Hosoya et al. (1989) J. Biochem. 105, 712-717). At the early stages of development, the amount of these isoforms was larger than those of alpha and beta isoforms. However, they gradually decreased at later stages and finally disappeared completely after hatching. By using two-dimensional gel electrophoresis and an image analyzing system, we examined the process of tropomyosin accumulation in gizzard smooth muscle development. The accumulation patterns of tropomyosin isoforms and their relative molar ratios to actin in embryonic development were different from those in the stages after hatching. The relative molar ratio of tropomyosin to actin in the thin filament preparation of embryonic gizzards was lower than that of adult, and it gradually increased in the course of embryonic development.

IgG1 plasmacytosis in interleukin 6 transgenic mice

Interleukin 6 (IL-6) has been suggested to be involved in the pathogenesis of polyclonal and monoclonal plasma cell abnormalities. To address this possibility, transgenic mice carrying the human IL-6 genomic gene fused with a human immunoglobulin heavy chain enhancer were generated. High concentrations of human IL-6 and polyclonal increase in IgG1 (120- to 400-fold) in sera of all transgenic mice were observed. A massive plasmacytosis in thymus, lymph node, and spleen and an infiltration of plasma cells in lung, liver, and kidney were observed. However, the plasma cells were not transplantable to syngeneic mice and were found not to contain chromosomal aberrations including c-myc gene rearrangements. The evidence indicates that deregulated gene expression of IL-6 can trigger polyclonal plasmacytosis but cannot induce plasmacytoma. It is suggested that additional genetic changes may be required for the generation of plasma cell neoplasia. Other interesting findings in these transgenic mice were the development of mesangio-proliferative glomerulonephritis and an increase in megakaryocytes in bone marrow.

Expression vector system based on the chicken beta-actin promoter directs efficient production of interleukin-5

We examined the promoter activity of the 1.3-kb chicken beta-actin gene sequence located between the 5' flanking region and the proximal region of the second exon. This promoter region showed higher promoter activity than the simian virus 40 (SV40) early promoter or the Rous sarcoma virus (RSV) long terminal repeat (LTR) as assayed by transient lacZ gene expression in mouse L cells. Furthermore, replacement of the 3' splice sequence in this promoter by that derived from the rabbit beta-globin gene resulted in a approximately 2.5-fold enhancement in the synthesis of beta-galactosidase (beta Gal). Introduction of the SV40 origin of DNA replication (ori) into the vector carrying this hybrid promoter, which we designate the AG promoter, markedly enhanced the production of beta Gal in an SV40 T antigen-producing cell, BMT10. We have constructed a useful vector containing the strong AG promoter, several unique restriction sites, a SV40 polyadenylation signal and the SV40 ori for transient expression of cDNA in BMT10 or COS cells. We demonstrate the use of this vector for efficient production of interleukin-5 in BMT10 cells.

Tropomyosin isoforms in developing chicken gizzard smooth muscle

In the embryonic smooth muscle of chicken gizzards we found 4 high-Mr-type and 5 low-Mr-type tropomyosin isoforms in addition to alpha- and beta-isoforms reported already. The criteria by which they were identified as tropomyosin isoforms were as follows: 1) anomalous reduction of electrophoretic mobility in the presence of urea, 2) cross reactivity with antisera against tropomyosins, 3) inclusion in a tropomyosin preparation obtained by the usual method for tropomyosin purification, and 4) binding ability to skeletal muscle actin. At the early stages of development, the amounts of these isoforms were larger than those of alpha- and beta-isoforms, but they gradually decreased at later stages and finally disappeared completely after hatching. Our previous study of gizzard smooth muscle showed that the amount ratio of accumulated tropomyosin to gamma-actin was reasonably constant in the development after hatching, while, at the earlier embryonic stages (7-14 d of incubation), it was lower than expected. The isoforms found in this study were present in amounts large enough to bring the ratio at the earlier stages up to the constant amount ratio observed after hatching. Therefore, the coordinate accumulation of actin and tropomyosin was suggested to occur even at the embryonic stages.

[Colon bladder replacement after total cystectomy]

Although ileal conduit diversion is widely accepted in the treatment of the patients undergoing radical cystectomy, many patients would prefer other alternatives which allow continence. and urination through the urethra. We describe a new procedure in which a segment of detuburalized right colon is used as a continent reservoir. Eight patients, 7 after radical cystectomy for bladder cancer and one after total exenteration for rectal cancer, have undergone colon bladder replacement. New created bladder had a capacity of 300 to 600 ml. All patients could pass urine through the urethra but one is on self-catheterization. Five of the 8 patients had no residual urine. Three months after operations 4 were totally continent and 3 were satisfactorily dry during daytime but slightly enuretic. Excretory urography showed no abnormalities in their upper urinary tract. Considering the "quality of life' of a patient, this procedure can be an ideal option for selected patients.

Demethylation by 5-azacytidine results in the expression of hepatitis B virus surface antigen in transgenic mice

In 14p3HB transgenic mice, which carry three tandem copies of hepatitis B virus (HBV) DNA, the HBV DNA was significantly methylated and no viral proteins were produced. To analyze the causal relationship between hypermethylation and gene inactivity, 5-azacytidine was injected into the mice to demethylate HBV DNA. When postnatal 14p3HB mice were treated with the drug, hepatitis virus surface antigen was produced in these mice by 3 weeks of age, and the integrated HBV DNA of the liver was less heavily methylated. Our results suggest that injection of 5-azacytidine can be used to efficiently activate a silent transgene such as HBV DNA in transgenic mice.

Expression and replication of hepatitis B virus genome in transgenic mice

We produced transgenic mice by microinjecting a partial tandem duplication of the complete hepatitis B virus (HBV) genome into fertilized eggs of C57BL/6 mice. One of eight transgenic mice was a high producer for HBV surface antigen (HBsAg) and HBV e antigen (HBeAg) in the serum. The HBV genomes were transmitted to the next generation and these F1 mice also produced HBsAg and HBeAg. mRNAs of 3.5, 2.1, and 0.8 kilobases were detected in the livers and the kidneys of these mice. In addition, a 0.8-kilobase RNA was detected in the testis. Single-stranded and partially double-stranded HBV DNAs were shown to be produced in the cytoplasm of the liver and kidneys. These HBV DNAs were associated with the core particles, indistinguishable from nucleocapsid produced in an infected human liver. Viral genome DNA was detected in the serum. These results demonstrate that the HBV genome integrated into the mouse chromosome acted as a template for viral gene expression, allowing viral replication. Thus, these transgenic mice should be useful for detailed studies of the replication and expression of HBV and for pathological studies of hepatitis, including the development of hepatocellular carcinoma.

Liver-specific and high-level expression of human serum amyloid P component gene in transgenic mice

To analyze the regulation of human serum amyloid P component (SAP) gene expression, we have produced seven transgenic mice. The 3.3 kb human SAP genes containing about 0.8 kb of 5' and 1.5 kb of 3' flanking region were injected into fertilized eggs of C57BL/6 mice. In five of the seven transgenic mice, human SAP was detected in the sera and serum concentrations were higher than that of human serum in three lines. The human SAP gene was expressed only in the liver. Amounts of human mRNA in the liver and serum concentrations of human SAP were roughly proportional to the copy number of the integrated gene. Human SAP production lowered the serum levels of mouse endogenous SAP. With the intraperitoneal administration of lipopolysaccharide, the mRNA levels in the liver and serum levels of mouse SAP increased several-fold in both the control and transgenic mice. On the other hand, neither the mRNA nor the serum levels of human SAP increased significantly.

Development of autoimmune insulitis is prevented in E alpha d but not in A beta k NOD transgenic mice

Two lines of E alpha d-expressing NOD mice were established by continuously backcrossing [E alpha d B6 transgenic mice x NOD] F1 to parental NOD or directly microinjecting the E alpha d gene into fertilized NOD eggs. Similarly, A beta k-expressing transgenic NOD mice were produced. Subsequent histological examination of pancreatic tissues revealed that autoimmune insulitis was prevented in E alpha d backcross and transgenic mice but not in A beta k transgenic mice.

Establishment of cell lines from somite stage mouse embryos and expression of major histocompatibility class I genes in these cells

To study the regulation of MHC class I gene expression during embryonic development, we have characterized a number of clonal cell lines derived from somite stage mouse embryos that were established with or without infection by several transforming retroviruses in combination with murine leukemia viruses. Unlike embryonal carcinoma (EC) cells that have been used as a model for early embryos, the cell lines derived from somite stage embryos are negative for stage specific embryonic Ag-1 and do not appear to differentiate after retinoic acid treatment. Morphology varies from clone to clone and is distinct from that of F9 and other EC cells. In agreement with previous findings in in vivo embryos, expression of surface MHC class I antigen in 57 new clones is either undetectable or low (with variability). All of the clones respond to the addition of interferons and express MHC class I antigens at high levels, but the kinetics of mRNA accumulation vary considerably. To examine the basis of the generally low or absent MHC class I gene expression in these cells, we tested promoter activity of a MHC class I gene by CAT assay after transient DNA transfection. Regardless of the basal levels of mRNA or surface Ag, CAT activity directed by various portions of the 5' flanking region of the MHC class I gene was uniformly low. The cells showed neither the negative nor the positive regulation of MHC class I genes that had been noted respectively for EC cells and for cells expressing the Ag constitutively. The pattern seen in the new cell lines suggests that there is an intermediate stage in the developmental regulation of MHC class I gene expression that may operate during the middle to late stage of fetal development.

Establishment of cell lines from somite stage mouse embryos and expression of major histocompatibility class I genes in these cells

To study the regulation of MHC class I gene expression during embryonic development, we have characterized a number of clonal cell lines derived from somite stage mouse embryos that were established with or without infection by several transforming retroviruses in combination with murine leukemia viruses. Unlike embryonal carcinoma (EC) cells that have been used as a model for early embryos, the cell lines derived from somite stage embryos are negative for stage specific embryonic Ag-1 and do not appear to differentiate after retinoic acid treatment. Morphology varies from clone to clone and is distinct from that of F9 and other EC cells. In agreement with previous findings in in vivo embryos, expression of surface MHC class I antigen in 57 new clones is either undetectable or low (with variability). All of the clones respond to the addition of interferons and express MHC class I antigens at high levels, but the kinetics of mRNA accumulation vary considerably. To examine the basis of the generally low or absent MHC class I gene expression in these cells, we tested promoter activity of a MHC class I gene by CAT assay after transient DNA transfection. Regardless of the basal levels of mRNA or surface Ag, CAT activity directed by various portions of the 5' flanking region of the MHC class I gene was uniformly low. The cells showed neither the negative nor the positive regulation of MHC class I genes that had been noted respectively for EC cells and for cells expressing the Ag constitutively. The pattern seen in the new cell lines suggests that there is an intermediate stage in the developmental regulation of MHC class I gene expression that may operate during the middle to late stage of fetal development.

An autosomal dominant mutation of facial development in a transgenic mouse

We have created a transgenic mouse which showed an autosomal dominant mutation of facial development. This facial malformation was characterized by a short snout and a twisted upper jaw. All offspring showing the dysmorphic phenotype carried the injected gene. In order to analyze the primary cause of this mutation, newborn mice and embryos were examined. The outcome was that the malformation of nasal and premaxillary bone was not the primary defect but was a secondary event. The primary cause of this dysmorphism was a developmental defect in the first branchial arch. Genomic DNA fragments flanking the insertion site of this mutant mouse were cloned. Using these fragments, we have assigned the integration site to chromosome 13. The gene responsible for a previously reported mutant mouse, one which also has a short snout, is also reported to be on chromosome 13. In the fragments flanking the insertion site of the transgenic mouse, at least one fragment was highly conserved in mammals. These results indicate that this malformation is due to the insertional disruption of a host gene. However, the possibility that this mutation is caused by an inappropriate expression of the injected gene still remains to be investigated.

Binding of multiple nuclear factors to the 5' upstream regulatory element of the murine major histocompatibility class I gene

Transcription of mouse major histocompatibility complex class I genes is controlled by the conserved class I regulatory element (CRE) in the 5' flanking region. The CRE, approximately 40 base pairs long, acts as a negative control element in undifferentiated F9 embryonal carcinoma cells which do not express the major histocompatibility complex genes. The same element, however, acts as a positive control element in cells expressing the genes at high levels. To investigate the molecular basis of the regulatory role of the CRE, we studied the binding of nuclear proteins to the CRE of the H-2Ld gene by gel mobility shift and methylation interference experiments. Nuclear extracts from L fibroblasts and LH8 T lymphocytes revealed three distinct factors that bind discrete sequences within the CRE. The three sequences correspond to the inverted and direct repeats within the CRE. In contrast, F9 extracts exhibited factor binding to only two of the three sequences and lack a major factor detected in the above two cell types. Protein-binding sites within each of the three sequences were identified by methylation interference experiments. These data were in full agreement with results obtained by a competition assay performed with a series of mutant oligonucleotides containing a few nucleotide substitutions in each of the three regions. The results illustrate complex DNA-protein interactions in which several independent proteins bind to overlapping sequences in the CRE in a cell type-specific fashion.

Introduction of H-2Dd determinants into the H-2Ld antigen by site-directed mutagenesis

We used site-directed mutagenesis to localize serologically defined (s) and CTL (c)-defined alloantigenic determinants to discrete amino acid sequences of a murine MHC class I antigen. Based on the prediction that amino acid position 63-73 of the H-2Dd antigen forms s-allodeterminants, the H-2Ld gene was mutated in a sequential fashion to replace codons for amino acid positions 63, 65, 66, 70, and 73 with those of the H-2Dd amino acids. Epitopes of the mutant antigens expressed in L-cells were examined by the binding of a series of mAbs specific for the H-2Dd antigen. The mutant antigen M66 had substitutions at residues 63, 65, and 66, and resulted in the acquisition of a number of H-2Dd-specific s-epitopes. Mutant M70 had an additional substitution at residue 70, which led to the gain of multiple additional H-2Dd s-epitopes. Together, more than half of all the relevant H-2Dd s-epitopes were mapped into amino acid position 63-70 of the H-2Dd molecule, which was expressed in the mutant H-2Ld gene. The final mutation at residue 73 (M73) caused no new epitope gains, rather, a few Dd s-epitopes acquired by the preceding mutations were lost. All of the H-2Ld-specific s-determinants were retained in the mutant molecules, as were H-2Dd s-determinants specific for the alpha-2 or alpha-3 domains. Changes of these residues affected c-determinants defined by CTL. Anti-H-2Dd CTL cultures and an anti-H-2Dd CTL clone recognized the mutant H-2Ld molecules, M66 and M70. Some CTL clones generated against the Q10d molecule, which has an identical sequence to H-2Dd between residues 61 and 73, failed to recognize native H-2Dd or Ld but did crossreact with mutant Ld. While bulk-cultured anti-H-2Ld CTL cultures reacted strongly against M73, bulk-cultured H-2Ld restricted anti-vesicular stomatitis virus CTL did not. Finally, at the clonal level two of three anti-H-2Ld CTL clones lost reactivity with some or all of these mutant molecules. From these results we conclude that a stretch of amino acids from position 63 to 70 of the alpha-1 domain controls major s- and c-antigenic sites on the H-2Dd antigen and c-sites on H-2Ld antigen.