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Papers by Dennis Loh

The Journal of Immunology, Dec 1, 2013

Eur J Immunol, 1989

A panel of geographically separate Mus m. domesticus and Swiss mice from several sources was scre... more A panel of geographically separate Mus m. domesticus and Swiss mice from several sources was screened for deletions in the T cell receptor variable (V) β locus. Four out of forty-three strains tested show a deletion identical to or larger than the deletion previously described in SJL mice. To our knowledge, this is the first time that such important Vβ deletions are described in inbred or partially inbred wild-derived strains of mice. On the other hand there seems to be very little polymorphism between the remaining Vβ genes. Expression of Vβ genes in peripheral and intra-thymic T cells was tested using antibodies specific for different Vβ polypeptide chains. Flow cytometry analysis revealed a high expression of Vβ6 and Vβ17 genes in the Copacabana Swiss-derived strain and an absence of Vβ17 expression in the WLA wild-derived strain.The three Mus m. domesticus strains (WLA, DDO and WBG) having deleted two to three additional Vβ subfamilies compared to SJL present no apparent immune deficiencies or autoimmune disorders. We conclude that relatively few Vβ genes may suffice for unimpaired survival of wild mice and that there is a selective pressure for the structural conservation of the remaining Vβ genes.

Science, 1994

CD8 is either an αα homodimer or an αβ heterodimer, although most peripheral CD8-lineage T cells ... more CD8 is either an αα homodimer or an αβ heterodimer, although most peripheral CD8-lineage T cells express only the CD8αβ heterodimer. The physiological function of CD8β was elucidated with mice that were chimeric for the homozygous disruption of the CD8β gene. The CD8β-/- T cells developed normally to CD4^+CD8^+ stage, but did not efficiently differentiate further, which resulted in few peripheral CD8^+ T cells. The number of peripheral CD8^+ T cells was restored by transfer of an exogenous CD8β gene into CD8β-deficient T cells. Thus, CD8β is necessary for the maturation of CD8^+ T cells.

Pnas, 1994

Mice carrying ablated coding regions of the bcl-2 alpha and bcl-2 beta transcripts have been made... more Mice carrying ablated coding regions of the bcl-2 alpha and bcl-2 beta transcripts have been made. bcl-2-/- mutants are smaller but viable, although about half of them die by 6 weeks of age. As shown earlier with somatic bcl-2 gene-targeted mice, the number of lymphocytes markedly decreased within few weeks after birth while other hematopoietic lineages remained unaffected. Among lymphocytes, CD8+ T cells disappeared most quickly followed by CD4+ T cells, whereas B cells were least affected. bcl-2-/- lymphocytes, however, could respond normally to various stimuli including anti-CD3, Con A, phorbol 12-myristate 13-acetate plus ionomycin, interleukin 2, lipopolysaccharide, and anti-IgM antibody. Abnormalities among nonlymphoid organs include smaller auricles, hair color turning gray at 4-5 weeks of age, and polycystic kidney disease-like change of renal tubules. These results suggest that Bcl-2 may be involved during morphogenesis where inductive interactions between epithelium and mesenchyme are important such as in the kidneys, hair follicles, and perichondrium of auricles. Surprisingly, the nervous system, intestines, and skin appear normal despite the fact that these organs show high levels of endogenous Bcl-2 expression in normal mice.

Proceedings of the National Academy of Sciences of the United States of America, Dec 1, 1989

To examine the effects of aberrant expression of class II major histocompatibility complex (MHC) ... more To examine the effects of aberrant expression of class II major histocompatibility complex (MHC) proteins on tolerance development, transgenic mice expressing the I-Ad genes under control of the pancreatic elastase promoter were produced. Such transgenic mice express I-Ad exclusively on exocrine pancreas, without expression in thymus or by lymphocytes. No spontaneous development of autoimmune reactivity toward exocrine pancreas was found in transgene-expressing mice of an H-2b background even though such mice could produce in vitro allogeneic responses against I-Ad. When T cells from nontransgenic H-2b mice as well as transgenic H-2b mice were activated in vitro by I-Ad allogeneic stimulator cells and transferred to transgenic mice, an intense, destructive lymphocytic infiltrate specific for exocrine pancreas developed. These findings suggest that aberrant class II MHC expression alone may not trigger autoimmune reactions. Rather, the unresponsiveness to allogenic class II MHC may result from the inability of exocrine pancreas to initiate primary responses by T cells.

Proceedings of the National Academy of Sciences of the United States of America, 1988

Science, 1993

The bcl-2 proto-oncogene can prevent the death of many cell types. Mice were generated that were ... more The bcl-2 proto-oncogene can prevent the death of many cell types. Mice were generated that were chimeric for the homozygous inactivation of bcl-2. Lymphocytes without Bcl-2 differentiated into phenotypically mature cells. However, in vitro, the mature T cells that lacked Bcl-2 had shorter life-spans and increased sensitivity to glucocorticoids and gamma-irradiation. In contrast, stimulation of CD3 inhibited the death of these cells. T and B cells with no Bcl-2 disappeared from the bone marrow, thymus, and periphery by 4 weeks of age. Thus, Bcl-2 was dispensable for lymphocyte maturation, but was required for a stable immune system after birth.

Immunogenetics, 1989

Our laboratory is involved in investigating the role of T-cell receptor (Tcr) in collagen-induced... more Our laboratory is involved in investigating the role of T-cell receptor (Tcr) in collagen-induced arthritis (CIA). During these studies we found AU/ssJ (H-2q) mice to be resistant to CIA like SWR (H-2q), as compared with other H-2q strains with wild-type Tcr like DBA/1 and B 10. Q. Upon screening with monoclonal antibodies F23.1 and KJ23a, AU/ssJ was found to be

1Abbreviations used in this ~tx'r: DN, double negative; DP, double positive; SP, single positive.

Science, 1993

The CD8α cytoplasmic domain associates with p56lck, a nonreceptor protein-tyrosine kinase. The bi... more The CD8α cytoplasmic domain associates with p56lck, a nonreceptor protein-tyrosine kinase. The biological relevance of CD8α-Lck association in T cell development was tested with transgenic mice generated to express a CD8α molecule with two amino acid substitutions in its cytoplasmic domain, which abolishes the association of CD8α with Lck. The CD8α mutant was analyzed in a CD8-/- background and in the context of the transgenic 2C T cell receptor. The development and function of CD8^+ T cells in these mice were apparently normal. Thus, CD8α-Lck association is not necessary for positive selection, negative selection, or CD8-dependent cytotoxic function.

Immunogenetics, 1988

The composition of 15 VTß gene subfamilies has been examined by Southern hybridization among a br... more The composition of 15 VTß gene subfamilies has been examined by Southern hybridization among a broad spectrum of colony bred rat and mouse species extending phylogenetically from Rattus to Mus musculus domesticus. Most mouse species contain a similar content of VTß genes as determined by the number of hybridizing restriction fragment (RF) bands. Furthermore, the extent of restriction fragment length

Nature, 1986

Variable processing of heteronuclear RNA into multiple, defined species of messenger RNA is a wel... more Variable processing of heteronuclear RNA into multiple, defined species of messenger RNA is a well-established phenomenon in a number of systems, including myelin basic protein, calcitonin, troponin T4 and immunoglobulins. Within a single B cell, immunoglobulin heavy-chain peptides often exist as two related but distinct species, a membrane-bound form and a secreted form, both of which originate from the same germline constant(C)-region gene via alternative RNA processing pathways. Furthermore, at certain stages of B-cell development, a single variable(V)-region element can be concurrently expressed in immunoglobulins of both the IgM and IgD isotypes, presumably resulting from the alternative splicing of one variable-region exon to different constant-region genes. We report here the existence of an alternative RNA splicing pathway available to murine T-cell receptor (TCR) beta-chain transcripts. Sequence analysis of beta-chain complementary DNA clones reveals a C beta 1 species containing a 72-base pair (bp) insertion between the joining (J beta) and C beta elements. This sequence is inserted via an alternative splicing pathway available to C beta 1 transcripts. The optional exon is located between the J beta 1 cluster and the first exon of C beta 1. Interestingly, this element can be spliced to C beta 2 in the New Zealand White mouse, in which the C beta 1 gene is deleted. Use of the alternative splicing pathway varies between 1% and 18% of total C beta clones, depending on the source of isolation.

Immunogenetics, 1989

Page 1. Immunogenetics 29: 180-185, 1989 hlllllUtlO-genetics Đ Springer-Verlag 1989 Identificatio... more Page 1. Immunogenetics 29: 180-185, 1989 hlllllUtlO-genetics Đ Springer-Verlag 1989 Identification of T-cell receptor deletion mutant mouse strain AU/ssJ (H-2 q) which is resistant to collagen-induced arthritis Tariq M. Haqqi ...

Proceedings of the National Academy of Sciences of the United States of America, Sep 1, 1997

An early stage in thymocyte development, after rearrangement of the beta chain genes of the T cel... more An early stage in thymocyte development, after rearrangement of the beta chain genes of the T cell receptor (TCR), involves expression of the pre-TCR complex and accompanying differentiation of CD4-CD8- double negative (DN) cells to CD4+CD8+ double positive (DP) cells. The ZAP-70 and Syk tyrosine kinases each contain two N-terminal SH2 domains that bind phosphorylated motifs in antigen receptor subunits and are implicated in pre-T receptor signaling. However, mice deficient in either ZAP-70 or Syk have no defect in the formation of DP thymocytes. Here we show that, in mice lacking both Syk and ZAP-70, DN thymocytes undergo beta chain gene rearrangement but fail to initiate clonal expansion and are incapable of differentiating into DP cells after expression of the pre-TCR. These data suggest that the ZAP-70 and Syk tyrosine kinases have crucial but overlapping functions in signaling from the pre-TCR and hence in early thymocyte development.

The Journal of Immunology, 1995

Transcriptional activation of rearranging Ag receptor gene segments has been hypothesized to regu... more Transcriptional activation of rearranging Ag receptor gene segments has been hypothesized to regulate their accessibility to V(D)J recombination. We analyzed the role of a functional promoter in the rearrangement of the murine TCR beta-chain locus using two transgenic minilocus constructs. These miniloci each contain an unrearranged V beta 8.3 gene. One has a wild-type V beta 8.3 gene, but the other has a V beta 8.3 gene with a promoter mutation that was previously shown to abrogate transcription in tissue culture. FACS analysis of thymus and lymph node cells from transgenic mouse lines showed that only the lines with the wild-type V beta 8.3 gene promoter express an 8.3 TCR beta-chain. Consistent with the protein expression data, V beta 8.3 gene transcripts were found only in the transgenic lines with the wild-type promoter. Using a quantitative PCR-based assay, it was shown that both types of transgenic lines recombine the V beta 8.3 gene at similar levels. Rearrangement of the transgenes was normal with respect to thymic development and junctional reading frame. Interestingly, both types of miniloci also underwent allelic exclusion in that recombination was blocked by the expression of a rearranged TCR beta-chain transgene. We conclude that a functional V beta gene promoter is not necessary for proper V(D)J recombination to occur.

Proceedings of the National Academy of Sciences of the United States of America, Dec 1, 1996

Stimulation of naive T cells by antigen-presenting cells (APC) is thought to involve two qualitat... more Stimulation of naive T cells by antigen-presenting cells (APC) is thought to involve two qualitatively different signals: signal one results from T-cell receptor (TCR) recognition of antigenic peptides bound to major histocompatibility complex (MHC) molecules, whereas signal two reflects contact with one or more costimulatory molecules. The requirements for stimulating naive T cells were studied with MHC class I-restricted CD8+ T cells from a T-cell receptor transgenic line, with defined peptides as antigen and transfected Drosophila cells as APC. Three main findings are reported. First, stimulation of naive T cells via signal one alone (MHC plus peptide) was essentially nonimmunogenic; thus T cells cultured with peptides presented by MHC class I-transfected Drosophila APC lacking costimulatory molecules showed little or no change in their surface phenotype. Second, cotransfection of two costimulatory molecules, B7-1 and intercellular adhesion molecule 1 (ICAM-1), converted class I+ Drosophila cells to potent APC capable of inducing strong T-proliferative responses and cytokine (interleukin 2) production. Third, B7-1 and ICAM-1 acted synergistically, indicating that signal two is complex; synergy between B7-1 and ICAM-1 varied from moderate to extreme and was influenced by both the dose and affinity of the peptide used and the parameter of T-cell activation studied. Transfected Drosophila cells are thus a useful tool for examining the minimal APC requirements for naive T cells.

The Journal of Immunology, Jul 1, 1998

Pnas, 1990

A specific interaction between the class I major histocompatibility complex molecule Kb and thymo... more A specific interaction between the class I major histocompatibility complex molecule Kb and thymocytes expressing the antigen receptor from the cytolytic T lymphocyte 2C enhances maturation of T cells of the CD8 lineage in transgenic mice. By analyzing transgenic mice backcrossed to Kbm mutant strains of mice, we have identified five bm mutations of the Kb antigen-encoding gene that alter the positive selection of thymocytes induced by Kb antigen. Compared with Kb, Kbm10 and Kbm1 did not induce significant maturation of 2C T-cell receptor-bearing thymocytes, and Kbm8 antigen positively selected for transgenic thymocytes only weakly. Altering residue 77 of Kb molecule from aspartic acid to serine made Kbm3 and Kbm11 allogeneic targets for the 2C antigen receptor and caused deletion of transgenic thymocytes. This deletion spared T cells that expressed low levels of CD8, a result differing from the total deletion of CD8-bearing T cells seen in mice that expressed the original target alloantigen Ld. This evidence indicates that (i) self-peptides bound to thymic major histocompatibility complex molecules can influence the positive selection of thymocytes and (ii) thymocytes with apparently weak interaction with self-major histocompatibility complex antigens can escape clonal deletion.

The Journal of Immunology, 1998

The Journal of Immunology, Dec 1, 2013

Eur J Immunol, 1989

A panel of geographically separate Mus m. domesticus and Swiss mice from several sources was scre... more A panel of geographically separate Mus m. domesticus and Swiss mice from several sources was screened for deletions in the T cell receptor variable (V) β locus. Four out of forty-three strains tested show a deletion identical to or larger than the deletion previously described in SJL mice. To our knowledge, this is the first time that such important Vβ deletions are described in inbred or partially inbred wild-derived strains of mice. On the other hand there seems to be very little polymorphism between the remaining Vβ genes. Expression of Vβ genes in peripheral and intra-thymic T cells was tested using antibodies specific for different Vβ polypeptide chains. Flow cytometry analysis revealed a high expression of Vβ6 and Vβ17 genes in the Copacabana Swiss-derived strain and an absence of Vβ17 expression in the WLA wild-derived strain.The three Mus m. domesticus strains (WLA, DDO and WBG) having deleted two to three additional Vβ subfamilies compared to SJL present no apparent immune deficiencies or autoimmune disorders. We conclude that relatively few Vβ genes may suffice for unimpaired survival of wild mice and that there is a selective pressure for the structural conservation of the remaining Vβ genes.

Science, 1994

CD8 is either an αα homodimer or an αβ heterodimer, although most peripheral CD8-lineage T cells ... more CD8 is either an αα homodimer or an αβ heterodimer, although most peripheral CD8-lineage T cells express only the CD8αβ heterodimer. The physiological function of CD8β was elucidated with mice that were chimeric for the homozygous disruption of the CD8β gene. The CD8β-/- T cells developed normally to CD4^+CD8^+ stage, but did not efficiently differentiate further, which resulted in few peripheral CD8^+ T cells. The number of peripheral CD8^+ T cells was restored by transfer of an exogenous CD8β gene into CD8β-deficient T cells. Thus, CD8β is necessary for the maturation of CD8^+ T cells.

Pnas, 1994

Mice carrying ablated coding regions of the bcl-2 alpha and bcl-2 beta transcripts have been made... more Mice carrying ablated coding regions of the bcl-2 alpha and bcl-2 beta transcripts have been made. bcl-2-/- mutants are smaller but viable, although about half of them die by 6 weeks of age. As shown earlier with somatic bcl-2 gene-targeted mice, the number of lymphocytes markedly decreased within few weeks after birth while other hematopoietic lineages remained unaffected. Among lymphocytes, CD8+ T cells disappeared most quickly followed by CD4+ T cells, whereas B cells were least affected. bcl-2-/- lymphocytes, however, could respond normally to various stimuli including anti-CD3, Con A, phorbol 12-myristate 13-acetate plus ionomycin, interleukin 2, lipopolysaccharide, and anti-IgM antibody. Abnormalities among nonlymphoid organs include smaller auricles, hair color turning gray at 4-5 weeks of age, and polycystic kidney disease-like change of renal tubules. These results suggest that Bcl-2 may be involved during morphogenesis where inductive interactions between epithelium and mesenchyme are important such as in the kidneys, hair follicles, and perichondrium of auricles. Surprisingly, the nervous system, intestines, and skin appear normal despite the fact that these organs show high levels of endogenous Bcl-2 expression in normal mice.

Proceedings of the National Academy of Sciences of the United States of America, Dec 1, 1989

To examine the effects of aberrant expression of class II major histocompatibility complex (MHC) ... more To examine the effects of aberrant expression of class II major histocompatibility complex (MHC) proteins on tolerance development, transgenic mice expressing the I-Ad genes under control of the pancreatic elastase promoter were produced. Such transgenic mice express I-Ad exclusively on exocrine pancreas, without expression in thymus or by lymphocytes. No spontaneous development of autoimmune reactivity toward exocrine pancreas was found in transgene-expressing mice of an H-2b background even though such mice could produce in vitro allogeneic responses against I-Ad. When T cells from nontransgenic H-2b mice as well as transgenic H-2b mice were activated in vitro by I-Ad allogeneic stimulator cells and transferred to transgenic mice, an intense, destructive lymphocytic infiltrate specific for exocrine pancreas developed. These findings suggest that aberrant class II MHC expression alone may not trigger autoimmune reactions. Rather, the unresponsiveness to allogenic class II MHC may result from the inability of exocrine pancreas to initiate primary responses by T cells.

Proceedings of the National Academy of Sciences of the United States of America, 1988

Science, 1993

The bcl-2 proto-oncogene can prevent the death of many cell types. Mice were generated that were ... more The bcl-2 proto-oncogene can prevent the death of many cell types. Mice were generated that were chimeric for the homozygous inactivation of bcl-2. Lymphocytes without Bcl-2 differentiated into phenotypically mature cells. However, in vitro, the mature T cells that lacked Bcl-2 had shorter life-spans and increased sensitivity to glucocorticoids and gamma-irradiation. In contrast, stimulation of CD3 inhibited the death of these cells. T and B cells with no Bcl-2 disappeared from the bone marrow, thymus, and periphery by 4 weeks of age. Thus, Bcl-2 was dispensable for lymphocyte maturation, but was required for a stable immune system after birth.

Immunogenetics, 1989

Our laboratory is involved in investigating the role of T-cell receptor (Tcr) in collagen-induced... more Our laboratory is involved in investigating the role of T-cell receptor (Tcr) in collagen-induced arthritis (CIA). During these studies we found AU/ssJ (H-2q) mice to be resistant to CIA like SWR (H-2q), as compared with other H-2q strains with wild-type Tcr like DBA/1 and B 10. Q. Upon screening with monoclonal antibodies F23.1 and KJ23a, AU/ssJ was found to be

1Abbreviations used in this ~tx'r: DN, double negative; DP, double positive; SP, single positive.

Science, 1993

The CD8α cytoplasmic domain associates with p56lck, a nonreceptor protein-tyrosine kinase. The bi... more The CD8α cytoplasmic domain associates with p56lck, a nonreceptor protein-tyrosine kinase. The biological relevance of CD8α-Lck association in T cell development was tested with transgenic mice generated to express a CD8α molecule with two amino acid substitutions in its cytoplasmic domain, which abolishes the association of CD8α with Lck. The CD8α mutant was analyzed in a CD8-/- background and in the context of the transgenic 2C T cell receptor. The development and function of CD8^+ T cells in these mice were apparently normal. Thus, CD8α-Lck association is not necessary for positive selection, negative selection, or CD8-dependent cytotoxic function.

Immunogenetics, 1988

The composition of 15 VTß gene subfamilies has been examined by Southern hybridization among a br... more The composition of 15 VTß gene subfamilies has been examined by Southern hybridization among a broad spectrum of colony bred rat and mouse species extending phylogenetically from Rattus to Mus musculus domesticus. Most mouse species contain a similar content of VTß genes as determined by the number of hybridizing restriction fragment (RF) bands. Furthermore, the extent of restriction fragment length

Nature, 1986

Variable processing of heteronuclear RNA into multiple, defined species of messenger RNA is a wel... more Variable processing of heteronuclear RNA into multiple, defined species of messenger RNA is a well-established phenomenon in a number of systems, including myelin basic protein, calcitonin, troponin T4 and immunoglobulins. Within a single B cell, immunoglobulin heavy-chain peptides often exist as two related but distinct species, a membrane-bound form and a secreted form, both of which originate from the same germline constant(C)-region gene via alternative RNA processing pathways. Furthermore, at certain stages of B-cell development, a single variable(V)-region element can be concurrently expressed in immunoglobulins of both the IgM and IgD isotypes, presumably resulting from the alternative splicing of one variable-region exon to different constant-region genes. We report here the existence of an alternative RNA splicing pathway available to murine T-cell receptor (TCR) beta-chain transcripts. Sequence analysis of beta-chain complementary DNA clones reveals a C beta 1 species containing a 72-base pair (bp) insertion between the joining (J beta) and C beta elements. This sequence is inserted via an alternative splicing pathway available to C beta 1 transcripts. The optional exon is located between the J beta 1 cluster and the first exon of C beta 1. Interestingly, this element can be spliced to C beta 2 in the New Zealand White mouse, in which the C beta 1 gene is deleted. Use of the alternative splicing pathway varies between 1% and 18% of total C beta clones, depending on the source of isolation.

Immunogenetics, 1989

Page 1. Immunogenetics 29: 180-185, 1989 hlllllUtlO-genetics Đ Springer-Verlag 1989 Identificatio... more Page 1. Immunogenetics 29: 180-185, 1989 hlllllUtlO-genetics Đ Springer-Verlag 1989 Identification of T-cell receptor deletion mutant mouse strain AU/ssJ (H-2 q) which is resistant to collagen-induced arthritis Tariq M. Haqqi ...

Proceedings of the National Academy of Sciences of the United States of America, Sep 1, 1997

An early stage in thymocyte development, after rearrangement of the beta chain genes of the T cel... more An early stage in thymocyte development, after rearrangement of the beta chain genes of the T cell receptor (TCR), involves expression of the pre-TCR complex and accompanying differentiation of CD4-CD8- double negative (DN) cells to CD4+CD8+ double positive (DP) cells. The ZAP-70 and Syk tyrosine kinases each contain two N-terminal SH2 domains that bind phosphorylated motifs in antigen receptor subunits and are implicated in pre-T receptor signaling. However, mice deficient in either ZAP-70 or Syk have no defect in the formation of DP thymocytes. Here we show that, in mice lacking both Syk and ZAP-70, DN thymocytes undergo beta chain gene rearrangement but fail to initiate clonal expansion and are incapable of differentiating into DP cells after expression of the pre-TCR. These data suggest that the ZAP-70 and Syk tyrosine kinases have crucial but overlapping functions in signaling from the pre-TCR and hence in early thymocyte development.

The Journal of Immunology, 1995

Transcriptional activation of rearranging Ag receptor gene segments has been hypothesized to regu... more Transcriptional activation of rearranging Ag receptor gene segments has been hypothesized to regulate their accessibility to V(D)J recombination. We analyzed the role of a functional promoter in the rearrangement of the murine TCR beta-chain locus using two transgenic minilocus constructs. These miniloci each contain an unrearranged V beta 8.3 gene. One has a wild-type V beta 8.3 gene, but the other has a V beta 8.3 gene with a promoter mutation that was previously shown to abrogate transcription in tissue culture. FACS analysis of thymus and lymph node cells from transgenic mouse lines showed that only the lines with the wild-type V beta 8.3 gene promoter express an 8.3 TCR beta-chain. Consistent with the protein expression data, V beta 8.3 gene transcripts were found only in the transgenic lines with the wild-type promoter. Using a quantitative PCR-based assay, it was shown that both types of transgenic lines recombine the V beta 8.3 gene at similar levels. Rearrangement of the transgenes was normal with respect to thymic development and junctional reading frame. Interestingly, both types of miniloci also underwent allelic exclusion in that recombination was blocked by the expression of a rearranged TCR beta-chain transgene. We conclude that a functional V beta gene promoter is not necessary for proper V(D)J recombination to occur.

Proceedings of the National Academy of Sciences of the United States of America, Dec 1, 1996

Stimulation of naive T cells by antigen-presenting cells (APC) is thought to involve two qualitat... more Stimulation of naive T cells by antigen-presenting cells (APC) is thought to involve two qualitatively different signals: signal one results from T-cell receptor (TCR) recognition of antigenic peptides bound to major histocompatibility complex (MHC) molecules, whereas signal two reflects contact with one or more costimulatory molecules. The requirements for stimulating naive T cells were studied with MHC class I-restricted CD8+ T cells from a T-cell receptor transgenic line, with defined peptides as antigen and transfected Drosophila cells as APC. Three main findings are reported. First, stimulation of naive T cells via signal one alone (MHC plus peptide) was essentially nonimmunogenic; thus T cells cultured with peptides presented by MHC class I-transfected Drosophila APC lacking costimulatory molecules showed little or no change in their surface phenotype. Second, cotransfection of two costimulatory molecules, B7-1 and intercellular adhesion molecule 1 (ICAM-1), converted class I+ Drosophila cells to potent APC capable of inducing strong T-proliferative responses and cytokine (interleukin 2) production. Third, B7-1 and ICAM-1 acted synergistically, indicating that signal two is complex; synergy between B7-1 and ICAM-1 varied from moderate to extreme and was influenced by both the dose and affinity of the peptide used and the parameter of T-cell activation studied. Transfected Drosophila cells are thus a useful tool for examining the minimal APC requirements for naive T cells.

The Journal of Immunology, Jul 1, 1998

Pnas, 1990

A specific interaction between the class I major histocompatibility complex molecule Kb and thymo... more A specific interaction between the class I major histocompatibility complex molecule Kb and thymocytes expressing the antigen receptor from the cytolytic T lymphocyte 2C enhances maturation of T cells of the CD8 lineage in transgenic mice. By analyzing transgenic mice backcrossed to Kbm mutant strains of mice, we have identified five bm mutations of the Kb antigen-encoding gene that alter the positive selection of thymocytes induced by Kb antigen. Compared with Kb, Kbm10 and Kbm1 did not induce significant maturation of 2C T-cell receptor-bearing thymocytes, and Kbm8 antigen positively selected for transgenic thymocytes only weakly. Altering residue 77 of Kb molecule from aspartic acid to serine made Kbm3 and Kbm11 allogeneic targets for the 2C antigen receptor and caused deletion of transgenic thymocytes. This deletion spared T cells that expressed low levels of CD8, a result differing from the total deletion of CD8-bearing T cells seen in mice that expressed the original target alloantigen Ld. This evidence indicates that (i) self-peptides bound to thymic major histocompatibility complex molecules can influence the positive selection of thymocytes and (ii) thymocytes with apparently weak interaction with self-major histocompatibility complex antigens can escape clonal deletion.

The Journal of Immunology, 1998