V. Ling et al., Differential expression of inducible costimulator-ligand splice variants: Lymphoid regulation of mouse GL50-B and human GL50 molecules, J IMMUNOL, 166(12), 2001, pp. 7300-7308
The process of immunological costimulation between APC and T cells is media
ted by protein ligand:receptor interactions. To date, costimulatory recepto
rs known to be expressed by T cells include the structurally related protei
ns CD28 and the inducible costimulator (ICOS). The ligands to human and mou
se ICOS, human GL50 (hGL50), and mouse GL50 (mGL50) were recently cloned an
d demonstrated to have sequence similarity to the CD28 ligands B7-1 and B7-
2. Examination of mGL50 cDNA transcripts by 3 ' RACE revealed an alternativ
ely spliced form, mGL50-B, that encoded a protein product with a divergent
27-aa intracellular domain. Both mGL50- and mGL50-B-transfected cells exhib
ited binding to human and mouse ICOS-Ig fusion protein, indicating that the
alternate cytoplasmic domain of mGL50-B does not interfere with extracellu
lar interactions with ICOS receptor. Flow cytometric and RT-PCR analysis of
BALB/c and RAG1(-/-) mice splenocytes demonstrate that freshly isolated B
cells, T cells, macrophages, and dendritic cells express both splice varian
t forms of ICOS ligand. Comparative analyses with the human ICOS ligand spl
ice variants hGL50 and B7-H2 indicate that differential splicing at the jun
ction of cytoplasmic exon 6 and exon 7 may be a common method by which GL50
-ICOS immunological costimulatory processes are regulated in vivo.