Biomedical subjects

M C Louie

Publications and source records attributed to M C Louie.

6 recordsLinked to original sources

PubMed1994

Requirement for CD8 beta chain in positive selection of CD8-lineage T cells.

CD8 is either an alpha alpha homodimer or an alpha beta heterodimer, although most peripheral CD8-lineage T cells express only the CD8 alpha beta heterodimer. The physiological function of CD8 beta was elucidated with mice that were chimeric for the homozygous disruption of the CD8 beta gene. The CD8 beta-1- 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 CD8 beta gene into CD8 beta-deficient T cells. Thus, CD8 beta is necessary for the maturation of CD8+ T cells.

Animals↗

PubMed1993

Thymic selection of cytotoxic T cells independent of CD8 alpha-Lck association.

The CD8 alpha cytoplasmic domain associates with p56lck, a nonreceptor protein-tyrosine kinase. The biological relevance of CD8 alpha-Lck association in T cell development was tested with transgenic mice generated to express a CD8 alpha molecule with two amino acid substitutions in its cytoplasmic domain, which abolishes the association of CD8 alpha with Lck. The CD8 alpha 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, CD8 alpha-Lck association is not necessary for positive selection, negative selection, or CD8-dependent cytotoxic function.

Animals↗

PubMed1993

Disappearance of the lymphoid system in Bcl-2 homozygous mutant chimeric mice.

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.

Animals↗

PubMed1993

The lack of CD8 alpha cytoplasmic domain resulted in a dramatic decrease in efficiency in thymic maturation but only a moderate reduction in cytotoxic function of CD8+ T lymphocytes.

The glycoprotein CD8 is believed to play an important role in the maturation and function of MHC class I-restricted T lymphocytes. CD8 has been proposed to function as a co-receptor of the TcR to participate in signal transduction, possibly through its cytoplasmic domain that binds to protein tyrosine kinase p56lck. A T cell-specific transgene encoding CD8 alpha truncated at the cytoplasmic domain ("tailless CD8 alpha"), was introduced into CD8 alpha-deficient mice. This animal model was used to study the role of the CD8 cytoplasmic domain in T cell ontogeny and function. "Tailless CD8 alpha" was expressed on the cell surface of thymocytes and peripheral T cells. A small population of peripheral CD4- T cells (6% of T lymphocytes) was found to have cell surface expression of "tailless CD8 alpha" and endogenous CD8 beta, indicating that these cells may belong to the CD8+ T cell lineage. A consistent result was obtained from CD8 alpha-deficient mice bearing the "tailless CD8 alpha" and the MHC class I-restricted 2C TcR transgenes. A small population of CD4- T cells expressing CD8 beta, the "tailless CD8 alpha" and the 2C TcR transgenes was present in the periphery of these mice in a selecting background, but was absent in a deleting background. When "tailless CD8 alpha" mice were infected with lymphocytic choriomeningitis virus (LCMV), the peripheral CD8+ CD4- T cell subset expanded dramatically and a significant LCMV-specific cytolytic activity was detected. The results suggest that the cytoplasmic portion of CD8 alpha is not absolutely required but dramatically enhances the efficiency of thymic maturation of CD8+ T cells. The lack of CD8 alpha cytoplasmic domain in peripheral CD8+ T cells does not abolish the generation of cytotoxicity in response to an in vivo LCMV infection, although the cytolytic activity is slightly reduced compared to that in control mice.

Animals↗

PubMed1989

Identification and characterization of new murine T cell receptor beta chain variable region (V beta) genes.

By screening previously isolated genomic clones spanning the mouse TCR V beta locus with V beta-specific oligonucleotides, we have isolated one new functional V beta gene and six V beta pseudogenes. Because this method of identifying new genes does not depend on expression levels, we conclude that most, if not all, V beta genes in the mouse have been identified. The newly identified pseudogenes increase the frequency of mouse TCR V beta pseudogenes to 28%, a frequency similar to that estimated for mouse Ig VH pseudogenes (24). Three of the newly discovered pseudogenes are clustered in a region around another pseudogene (V beta 17b). The extensive DNA diversity, as reflected in both the nucleotide sequence and the RFLP, indicates that this genomic region is a possible hotspot of recombination. The new functional gene, V beta 19a, is expressed at very low levels, which explains why it has not been isolated earlier. V beta 19 shows expression patterns that correlate with the previously described Va beta and Vb beta haplotypes.

Amino Acid Sequence↗

PubMed1987

Tandem linkage and unusual RNA splicing of the T-cell receptor beta-chain variable-region genes.

The variable-region (V) genes of the murine T-cell receptor beta chain exist largely as single-element subfamilies. The V beta 5 and V beta 8 genes belong to the only two known three-member V beta subfamilies. We present studies on the linkage of these six genes and show that the genomic organization is that of alternating V beta 5 and V beta 8 genes. Our analysis suggests that these genes were tandemly duplicated, the unit of duplication being a pair of V beta 5 and V beta 8 genes. This tandem organization permits transcripts to initiate from the promoter of an unrearranged V beta located upstream of the rearranged V beta gene. These transcripts can generate functional beta-chain gene messages by novel RNA splicing of the upstream leader exon to the V beta coding exon of the downstream rearranged gene. We extend the analysis of the T-cell receptor genomic organization to include 12 V beta genes and suggest that all V beta genes are closely linked on chromosome 6. In addition, we discuss the possible implications of the close linkage of the V beta genes on the development of the T-cell receptor beta-chain gene repertoire.

Amino Acid Sequence↗