Signal transduction in human B cells initiated via Ig{beta} ligation

Ig and Igß heterodimers are non-covalently associatedwith Ig to compose the antigen receptor complexes on B cells.The demonstration that different sets of tyrosine kinases bindto the cytoplasmic tails of Ig and Igß suggests thatIg and Igß may activate distinct second messengerpathways. In this study, we examined the effects of mAbs againstan exposed epitope of human Igß on pre-B and B celltriggering. Cross-linkage of Igß on B cells leadsto activation of tyrosine kinases, hydrolysis of phosphatidylinositides,and elevation of intracellular Ca²⁺, effects qualitatively identicalto those of anti-_µ mAbs. Our observations thus indicatethat cross-linking of Igß does not segregate signaltransduction pathways connected with the cytoplasmic talls ofIg and Igß. Ig ligation has been reported to be moreeffective in triggering pre-B than B cells, whereas our resultsindicated that Igß ligation is more efficient in triggeringB than pre-B cells. In addition to their activation properties,the anti-Igß mAbs effectively modulated B cell receptorcomplexes and blocked terminal differentiation of all plasmacell isotypes. The findings support the idea that anti-Igßcould serve as a universal B cell immunosuppressant.     

Characterization of evolutionary rates and constraints in three Mammalian genomes

We present an analysis of rates and patterns of microevolutionary phenomena that have shaped the human, mouse, and rat genomes since their last common ancestor. We find evidence for a shift in the mutational spectrum between the mouse and rat lineages, with the net effect being a relative increase in GC content in the rat genome. Our estimate for the neutral point substitution rate separating the two rodents is 0.196 substitutions per site, and 0.65 substitutions per site for the tree relating all three mammals. Small insertions and deletions of 1-10 bp in length ("microindels") occur at approximately 5% of the point substitution rate. Inferred regional correlations in evolutionary rates between lineages and between types of sites support the idea that rates of evolution are influenced by local genomic or cell biological context. No substantial correlations between rates of point substitutions and rates of microindels are found, however, implying that the influences that affect these processes are distinct. Finally, we have identified those regions in the human genome that are evolving slowly, which are likely to include functional elements important to human biology. At least 5% of the human genome is under substantial constraint, most of which is noncoding.     

Cloning and sequencing of the cDNA encoding the human homologue of the murine immunoglobulin-associated protein B29.

Membrane-bound immunoglobulins (Ig) on the surface of murine B cells are noncovalently associated with a heterodimeric protein complex of MB-1 and B29 (also called Ig-alpha and Ig-beta). The Ig-associated proteins are predicted to regulate the assembly and transport of the Ig complex to the cell surface and to couple membrane-bound Ig to intracellular signal transduction pathways. We have isolated and sequenced a full-length cDNA clone encoding the human homologue of the B29 protein. The predicted amino acid sequence was compared to its murine counterpart, to MB-1 and to the human T cell receptor (TcR)-associated CD3 proteins. The alignment of the human B29 protein with its murine counterpart revealed 90% homology in the C-terminal portion comprising the cytoplasmic tails, the transmembrane regions and the adjacent 26 amino acids of the extracellular regions. Only 59% homology was found in the rest of the Ig-like extracellular domains. The high degree of conservation observed for the C-terminal amino acids suggested that these domains of the proteins play important functional roles for the Ig complex. Indicative of this was the conservation of the antigen receptor tail motif D-(X)7-E/D-(X)2-Y-(X)2-L-(X)7-Y-(X)2-L/I which is thought to be a component of signal transduction pathways. This motif is also found in the human and murine MB-1 proteins as well as in the TcR-associated CD3 molecules. Further regions of homology between B29, MB-1 and the CD3 proteins included extracellular residues which were predicted to maintain the Ig-like structure, and hydrophilic residues within the transmembrane regions which may be utilized during the intracellular assembly and transport of the oligomeric Ig/MB-1/B29 or TcR/CD3 complexes. Thus the similarities found between B29, MB-1 and the CD3 proteins suggest conserved functions for both the Ig- and TcR-associated proteins.     

Simultaneous turnover of normal and dysfunctional C1 inhibitor as a probe of in vivo activation of C1 and contact activatable proteases.

Simultaneous turnover of normal and dysfunctional C1-inhibitor (C1-INH) was carried out in 10 normal subjects and 13 patients with rheumatoid arthritis as a measure of the in vivo activation of C1 and the contact activatable enzymes. In the first series of experiments, dysfunctional protein We was used in simultaneous turnover studies in five normal subjects and nine patients. The fractional catabolic rate of the dysfunctional C1-INH, We, (FCR(d)) was unchanged in both groups but the fractional catabolic rate of the normal C1-INH (FCR(n)) was faster in the patients compared to the controls, in particular patients with vasculitis. The enzyme-dependent catabolism defined as FCR(n-d) X concentration of C1-INH X plasma volume, was raised in the patient group, and correlated with disease activity score (r = 0.83, P less than 0.05). Neither FCR(n) nor FCR(d) was dependent on C1-INH concentration. The latter was higher in the patients (206 mg/l compared with 155 mg/l) indicating a very high synthetic rate in the patients (280.81 micrograms/kg/h compared with 179.77 micrograms/kg). In the second series of turnovers in six patients and five normal subjects, another dysfunctional C1-INH, at, was used. The FCR of C1-INH was slower than C1-INH (We) (1.88%/h compared with 2.7%/h). Enzyme-dependent catabolism of C1-INH in these patients were raised and also correlated with disease activity score (r = 0.82, P less than 0.05).     

Effect of surface hydrophilicity on ex vivo blood compatibility of segmented polyurethanes

The relationship between surface, bulk and ex vivo blood-contacting properties of segmented polyurethanes with various polyol soft segment was investigated. The polyols used in this study were poly(ethylene oxide), poly(tetramethylene oxide), hydrogenated poly(butadiene), poly(butadiene) and poly(dimethylsiloxane). The hard segment of these segmented polyurethanes was composed of 4,4' diphenylmethane diisocyanate and 1,4 butanediol, present at 50 wt%. An experimental polyurethane, Biostable PUR, which has shown excellent biostability, was used in this study. The segmented polyurethanes based on the hydrophobic polyols such as poly(dimethylsiloxane) and hydrogenated poly(butadiene) showed distinct microphase separation between hard and soft segments. X-ray photoelectron spectroscopy revealed the surface enrichment of the hydrophobic component at the air-solid interface. Dynamic contact angle measurements indicated that the poly(dimethylsiloxane)-based segmented polyurethane possessed a hydrophobic surface in water. The poly(dimethylsiloxane)-based segmented polyurethane had the lowest platelet adhesion among the segmented polyurethanes investigated in this study, whilst the platelet deposition on the poly(ethylene oxide)-based polymer increased with time.     

Mesenchymal stem cells

The tremendous capacity of bone to regenerate is indicative of the presence of stem cells with the capability, by definition, to self-renew as well as to give rise to daughter cells. These primitive progenitors, termed mesenchymal stem cells or bone marrow stromal stem cells, exist postnatally, and are multipotent with the ability to generate cartilage, bone, muscle, tendon, ligament, and fat. Given the demographic challenge of an ageing population, the development of strategies to exploit the potential of stem cells to augment bone formation to replace or restore the function of traumatized, diseased, or degenerated bone is a major clinical and socioeconomic need. Owing to the developmental plasticity of mesenchymal stem cells, there is great interest in their application to replace damaged tissues. Combined with modern advances in gene therapy and tissue engineering, they have the potential to improve the quality of life for many. Critical in the development of this field will be an understanding of the phenotype, plasticity, and potentiality of these cells and the tempering of patients' expectations driven by commercial and media hype to match current laboratory and clinical observations.     

Seasonal abundance of Anopheles farauti (Diptera: Culicidae) sibling species in far north Queensland, Australia

In the Cairns area of far north Queensland, Australia, the seasonal abundance of Anopheles farauti Laveran sibling species was studied at 6 locations, representing 3 habitat types, between August 1995 and September 1997. A total of 45,401 An. farauti s.l. was collected using CO2 + octenol baited CDC light traps, and consisted of 29,565 An. farauti No. 2, 14,214 An. farauti No. 3, and 1,622 An. farauti s.s. The relative abundance of all 3 species differed significantly by season and location. An. farauti No.2 was the dominant species except in Cairns, where An. farauti s.s. was most abundant, and at Ninds Creek, where An. farauti No. 3 predominated. The dominant species at each location was present year round, although peaks in seasonal abundance were observed. An. farauti s.s. populations were highest during the wet season (January-April). In lowland freshwater swamp habitats and 1 brackish location, An. farauti No. 2 was more abundant during the wet season. However, at the highland freshwater swamp habitat, populations of An. farauti No. 2 were highest during the late dry season and early wet season (October-December). There was a significant positive correlation of both temperature and rainfall with An. farauti s.s. and An. farauti No. 2 trap collections. There was a negative correlation between An. farauti No. 3 and temperature, indicating that this species may be more abundant during cool weather. Although there were significant relationships among weather variables and An. farauti s.l. collections, correlation values were generally low, indicating that other factors may contribute to variability among An. farauti sibling species trap collections.     

Localisation of a gene for prepubertal periodontitis to chromosome 11q14 and identification of a cathepsin C gene mutation

Prepubertal periodontitis (PPP) is a rare and rapidly progressive disease of young children that results in destruction of the periodontal support of the primary dentition. The condition may occur as part of a recognised syndrome or may occur as an isolated finding. Both autosomal dominant and recessive forms of Mendelian transmission have been reported for PPP. We report a consanguineous Jordanian family with four members affected by PPP in two nuclear sibships. The parents of the affected subjects are first cousins. We have localised a gene of major effect for PPP in this kindred (Zmax=3.55 for D11S901 at θ=0.00) to a 14 cM genetic interval on chromosome 11q14 flanked by D11S916 and D11S1367. This PPP candidate interval overlaps the region of chromosome 11q14 that contains the cathepsin C gene responsible for Papillon-Lefèvre and Haim-Munk syndromes. Sequence analysis of the cathepsin C gene from PPP affected subjects from this Jordanian family indicated that all were homozygous for a missense mutation (1040A→G) that changes a tyrosine to a cysteine. All four parents were heterozygous carriers of this Tyr347Cys cathepsin C mutation. None of the family members who were heterozygous carriers for this mutation showed any clinical findings of PPP. None of the 50 controls tested were found to have this Tyr347Cys mutation. This is the first reported gene mutation for non-syndromic periodontitis and shows that non-syndromic PPP is an allelic variant of the type IV palmoplantar ectodermal dysplasias.


Keywords: prepubertal periodontitis; periodontal disease; cathepsin C; linkage