Regulation of in vitro and in vivo T cell activation by CD43

Accessory molecule interactions can be critical in determining the outcome of a T cell's encounter with antigen. Cell adhesion proteins may augment T cell responses by facilitating TCR engagement of the antigen-MHC complex, while co-stimulatory molecules may deliver distinct signals that modulate T cell responsiveness. CD43 (leukosialin, sialophorin) has been suggested to influence cell activation by steric hindrance based upon the large size and glycosylation of the protein, as well as the relative abundance of the protein on the cell surface. In this paper we examine both in vitro and in vivo T cell-dependent responses in CD43-deficient mice. We demonstrate that T cells from CD43-deficient mice are hyper-responsive following both in vivo and in vitro activation, and that this is observed in response to not only TCR-CD3-mediated stimulation, but also following receptor-independent activation. This data suggests that mechanisms other than non-specific steric hindrance are important in the regulation of T cell activation by CD43.      

A G-->A transition creates a branch point sequence and activation of a cryptic exon, resulting in the hereditary disorder neurofibromatosis 2

We describe a G-->A transition within intron 5 of the NF2 gene. This mutation creates a consensus splice branch point sequence. To our knowledge this is the first report of a mutation that creates a functional branch point sequence in a human hereditary disorder. The new branch point sequence is located 18 bp upstream of a consensus splice acceptor site. A consensus splice donor site is found 106 bp 3' of the acceptor site. Asa consequence the G-->A transition results in an alternatively spliced mRNA containing an additional exon 5a of 106 bp derived from intron sequences. We cloned the mutant cDNA and show that due to an in-frame stop codon the cDNA codes for a truncated NF2 protein. The mutation was observed in three affected members of an NF2 family. In a tumour of one of the family members both alternatively spliced and wild-type mRNA were found, although the wild-type allele of the gene is absent due to an interstitial deletion on chromosome 22. We also show that immunoprecipitations reveal the presence of full-length wild-type NF2 protein in the tumour lysate. These data support the hypothesis that some degree of normal splicing of the mutant precursor RNA is taking place. It is therefore likely that this residual activity of the mutant allele explains the relatively mild phenotype in the family. These data also indicate that complete inactivation of the gene is not required for tumour formation.      

Gated MR imaging of left atrial myxomas

Two cases of left atrial myxoma were evaluated with magnetic resonance (MR) imaging. In both cases, the myxoma was clearly defined as to its location, origin, and size. In one case, the myxoma prolapsed through the mitral valve. Our study indicates that MR imaging is valuable in the diagnosis of myxomas.     

Prekallikrein-Kallikrein conversion rate as a predictor of contrast material catastrophies

An in vitro is described that attempts to detect patients with a potential for adverse systemic reactions to contrast material. This test involves measuring the rate of conversion of prekallikrein to kallikrein under certain standard conditions. In a preliminary retrospective study, the test could be used to identify such patients with a sensitivity of 88%, a specificity of 82%, and a predictive value of 79%.