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CD45 alternative exon expression in murine and human CD4+ T cell subsets
P R Rogers1, S Pilapil, K Hayakawa
1Department of Molecular Genetics and Microbiology, University of Massachusetts Medical School, Worcester 01655.
Journal of Immunology (Baltimore, Md. : 1950)
|June 15, 1992
Summary
Leukocyte common antigen (CD45) isoforms are generated by exon splicing. This study found CD45 isoform differences in T cells stem from overall variable exon levels, not specific exon ratios, with human T cells expressing more CD45 variable exons.
Area of Science:
- Immunology
- Molecular Biology
- Cell Biology
Background:
- Leukocytes express leukocyte common antigen (CD45), a glycoprotein crucial for phosphotyrosine signal transduction.
- Different CD45 isoforms, generated by cell-type and differentiation-specific exon splicing, distinguish functionally distinct CD4+ T cell subsets.
- Splicing of variable exons A, B, and C can produce eight distinct CD45 mRNA transcripts.
Purpose of the Study:
- To quantify the relative abundance of all eight CD45 mRNA transcripts in murine CD4+ T cell lines and normal murine and human CD4+ T cell subsets.
- To investigate how differential splicing of CD45 variable exons contributes to isoform diversity in T cells.
Main Methods:
- Utilized antibodies targeting CD45 variable exons to isolate murine and human CD4+ T cell subsets.
- Quantified the relative levels of eight different CD45 mRNA transcripts in isolated T cell populations using molecular techniques.
Main Results:
- The overall expression patterns of CD45 isoforms on T cell surfaces correlate with the relative abundance of the eight differentially spliced transcripts.
- Unexpectedly, variations in CD45 isoform expression among CD4+ T cell subpopulations were solely attributable to differences in the total level of variable exon expression.
- No significant differences were observed in the relative expression ratios of individual variable exons (A, B, C) across T cell populations.
- Exon B was consistently more abundant than exons C or A; only AB and BC dual exon species were detected, while AC was undetectable.
- Human CD4+ T cells, particularly naive subsets, exhibit higher overall expression of CD45 variable exons compared to murine CD4+ T cells.
Conclusions:
- CD45 isoform heterogeneity in CD4+ T cells is primarily regulated by the overall level of variable exon inclusion, rather than differential splicing of specific exons.
- The relative abundance of specific variable exons (B > C > A) and the presence of AB and BC splice variants are conserved features in CD4+ T cells.
- Human naive T cells show a distinct pattern of higher CD45 variable exon expression compared to their murine counterparts.