A mutation in the human tetraspanin CD81 gene is expressed as a truncated protein but does not enable CD19 maturation and cell surface expression.

A homozygous mutation in a splice site of the CD81 gene was identified previously in a patient, as the cause in a case of common variable immune deficiency (CVID). CD19 expression is reduced in mice that lack CD81; however, B cells in this patient lacked completely CD19 surface expression. The mutation led to an absence of the CD81 protein on the cell surface and it was assumed that the CD81 protein was not produced. Here we demonstrate that a truncated human CD81 mutant (CD81mut) was actually produced, but retained intracellularly. We also demonstrate that the truncated CD81mut protein is in close proximity to the intracellularly sequestered CD19. However, this interaction does not enable normal CD19 maturation and surface expression. In addition, we show that specific domains of CD81 enable retrieval and trafficking of human CD19 to the cell surface. Finally, we demonstrate that surface expression of CD19 requires CD81, even in non-B cells.

Reliable determination of transposon insertion site in prokaryotes by direct sequencing.

We developed a method to identify the insertion sites of transposons in the chromosome of Salmonella using one step only. In this method, the Salmonella's genomic DNA is directly sequenced using a transposon internal primer. Reliable direct sequencing was achieved using high purity genomic DNA and an improved protocol for automated sequence machine. This note is intended to promote the use of direct sequencing, which we found to be reliable, efficient and inexpensive as compared to the other currently used methods.

Involvement of phosphodiesterases in autoimmune diseases.

We have previously shown that several phosphodiesterase (PDE) subtypes are up-regulated in muscles and lymph node cells (LNC) of rats with experimental autoimmune myasthenia gravis (EAMG). In the present study we investigated PDE expression during the course of EAMG and experimental allergic encephalomyelitis (EAE) and found that the up-regulated expression of selected PDE subtypes in both experimental models is correlated with disease severity. In EAMG, PDE expression is correlated also with muscle damage. A similar up-regulation of PDE was also observed in the respective human diseases, MG and multiple sclerosis (MS). Our findings suggest that change in PDE expression levels is a general phenomenon in autoimmune diseases and may also be used as a marker for disease severity.

Autoimmune spread to myelin is associated with experimental autoimmune encephalomyelitis induced by a neuronal protein, beta-synuclein.

Accumulating evidence suggests that autoimmunity against neuronal proteins is important for MS pathogenesis. We have characterized T- and B-cell responses associated with experimental autoimmune encephalomyelitis (EAE) induced in Lewis rats with recombinant beta-Synuclein (betaSync), a neuronal component. The encephalitogenic betaSync-specific T cells recognize a single immunodominant region with an epitope delineated at amino acids 97-105; B-cell specificity is more widespread, albeit directed mostly to the C-terminus of betaSync. Most interestingly, betaSync-induced autoimmune T- and B-cell responses spread not only to other neuronal antigens but also to myelin encephalitogens, raising the possibility that anti-neuronal immune attacks could also result in demyelination.

Identification of Salmonella typhimurium genes responsible for interference with peptide presentation on MHC class I molecules: Deltayej Salmonella mutants induce superior CD8+ T-cell responses.

Salmonella-derived epitopes are presented on MHC molecules by antigen-presenting cells, and both CD4+ and CD8+ T cells participate in protective immunity to Salmonella. Therefore, mechanisms that allow Salmonella to escape specific immune recognition are likely to have evolved in this bacterial pathogen. To identify Salmonella genes, which potentially interfere with the MHC class I (MHC-I) presentation pathway, Tn10d transposon mutagenesis was performed. More than 3000 mutants, statistically covering half of the Salmonella genome, were individually screened for altered peptide presentation by infected macrophages. Two mutants undergoing enhanced antigen presentation by macrophages were identified, carrying a Tn10d insertion in the yej operon. This phenotype was validated by specific inactivation and complementation experiments. In accordance with their enhanced MHC-I presentation phenotype, we showed that (i) specific CD8+ T cells were elicited at a higher level in mice, in response to immunization with yej mutants compared to their parental strain in two different experimental settings; and (ii) yej mutants were superior vaccine carriers for heterologous antigens compared to the parental strain in a tumour model.