Defective Vav expression and impaired F-actin reorganization in a subset of patients with common variable immunodeficiency characterized by T-cell defects.

Common variable immunodeficiency (CVID) is a primary immune disorder characterized by impaired antibody production, which is in many instances secondary to defective T-cell function (T-CVID). We have previously identified a subset of patients with T-CVID characterized by defective T-cell receptor (TCR)-dependent protein tyrosine phosphorylation. In these patients, ZAP-70 fails to be recruited to the TCR as the result of impaired CD3zeta phosphorylation, which is, however, not dependent on defective Lck expression or activity. Here we show that neither Fyn nor CD45 is affected in these patients. On the other hand, T-CVID T cells show dramatic defects in the Vav/Rac pathway controlling F-actin dynamics. A significant deficiency in Vav protein was indeed observed; in 3 of 4 patients with T-CVID, it was associated with reduced VAV1 mRNA levels. The impairment in Vav expression correlated with defective F-actin reorganization in response to TCR/CD28 co-engagement. Furthermore, TCR/CD28-dependent up-regulation of lipid rafts at the cell surface, which requires F-actin dynamics, was impaired in these patients. The actin cytoskeleton defect could be reversed by reconstitution of Vav1 expression in the patients' T cells. Results demonstrate an essential role of Vav in human T cells and strongly suggest Vav insufficiency in T-CVID.

The Helicobacter pylori vacuolating toxin inhibits T cell activation by two independent mechanisms.

Helicobacter pylori toxin, VacA, damages the gastric epithelium by erosion and loosening of tight junctions. Here we report that VacA also interferes with T cell activation by two different mechanisms. Formation of anion-specific channels by VacA prevents calcium influx from the extracellular milieu. The transcription factor NF-AT thus fails to translocate to the nucleus and activate key cytokine genes. A second, channel-independent mechanism involves activation of intracellular signaling through the mitogen-activated protein kinases MKK3/6 and p38 and the Rac-specific nucleotide exchange factor, Vav. As a consequence of aberrant Rac activation, disordered actin polymerization is stimulated. The resulting defects in T cell activation may help H. pylori to prevent an effective immune response leading to chronic colonization of its gastric niche.

Cloning of the murine non-muscle myosin heavy chain IIA gene ortholog of human MYH9 responsible for May-Hegglin, Sebastian, Fechtner, and Epstein syndromes.

Mutations in the non-muscle myosin heavy chain IIA gene (MYH9) are responsible for May-Hegglin anomaly, Sebastian, Fechtner and Epstein syndromes. These 'MYH9-related' diseases are inherited as an autosomal dominant trait and are characterized by a variable expressivity of clinical features, including macrothrombocytopenia, deafness, nephrites, cataract, and Döhle-like leukocyte inclusions. To gain information of the function of the non-muscle myosin heavy chain IIA protein (NMMHC-IIA), we have identified the murine orthologue Myh9 gene. The gene is localized in a region of chromosome 15 and encodes a predicted protein of 1960 amino acids. This protein shows a high homology to the human NMMHC-IIA with 98% identity. The Myh9 exon-intron junctions were deduced from a murine genomic clone that revealed a perfect conservation of the exon structure between the human and mouse gene. Myh9 is expressed in liver, kidney, lung, and spleen. A low level of transcripts was detected also in heart and brain while no expression was revealed in skeletal muscle and testis. In vertebrates, NMMHC-IIA shows a striking degree of homology to NMMHC-IIB, which is expressed at higher level in mouse brain and testis than in other tissues, confirming the hypothesis that the two non-muscle myosins have different functional roles within cells.

Nonsteroidal anti-inflammatory drugs suppress T-cell activation by inhibiting p38 MAPK induction.

In addition to antagonizing inflammation by inhibiting the activity of cyclooxygenases (COX), nonsteroidal anti-inflammatory drugs (NSAID) block T-cell activation. The immunosuppressant activity of NSAID correlates with their ability to block transcription factors required for the expression of inducible response genes triggered by T-cell antigen receptor (TCR) engagement. Whereas the inhibition of nuclear factor-kappaB by aspirin and sodium salicylate can be partly accounted for by their binding to IkappaB kinase-beta, the broad range of transcriptional targets of NSAID suggests that the products of COX activity might affect one or more among the early steps in the TCR-signaling cascade. Here we show that the inhibition of NF-AT activation by NSAID correlates with a selective inhibition of p38 MAP kinase induction. The suppression of TCR-dependent p38 activation by NSAID can be fully overcome by prostaglandin E(2), underlining the requirement for COX activity in p38 activation. Furthermore, the inhibition of COX-1 results in defective induction of the COX-2 gene, which behaves as an early TCR responsive gene. The data identify COX-1 and COX-2 as integral and sequential components of TCR signaling to p38 and contribute to elucidate the molecular basis of immunosuppression by NSAID.