Immunoglobulins to group A streptococcal surface molecules decrease adherence to and invasion of human pharyngeal cells

The M protein is one of the most important virulence factors of group A streptococci (Streptococcus pyogenes) and may play an important role in the first steps of streptococcal infection. Since acute pharyngitis is a frequently occurring infectious disease caused by these bacteria, we wished to know whether antibodies to the M protein or other surface components inhibit adherence and internalization of streptococci to pharyngeal cells. We investigated the role of whole human secretory immunoglobulin A (sIgA), M6 protein-specific sIgA, and M6 protein-specific serum IgG in the inhibition of streptococcal adherence and internalization to cultured human pharyngeal cells. S. pyogenes D471, which produces a type 6 M protein (M+), and its isogenic M-negative (M-) derivative JRS75 were tested. Purified whole sIgA, M protein-specific sIgA, and sIgA preabsorbed with M protein were able to decrease significantly the adherence of streptococci to pharyngeal cells. Purified IgG against the M6 protein did not diminish the attachment of streptococci to the pharyngeal cells but did reduce internalization. Thus, our data suggest that secretory IgA may play a key role in preventing streptococcal infection at mucosal surfaces by blocking adherence while affinity-purified anti-M protein-specific IgG blocks epitopes responsible for invasion.     

Cell mediated immune response in chronic liver diseases: schistosomal, viral and neoplastic

Cell mediated immune response (CMIR) was studies in 120 patients having chronic liver diseases. Patients were divided into 6 groups, (20 each). (1) Early hepatosplenic Schistosomiasis. (EHSS), (2) Late hepatosplenic Schistosomiasis. (LHSS), (3) Hepatosplenic Schistosomiasis with hepatitis B and/or C infections, (4) Hepatitis B virus cases. (HBV), (5) Hepatitis C virus cases (HCV), (6) Hepatocellular carcinoma cases. (HCC). Twenty within normal subjects taken as controls. Laboratory investigations revealed significant esinophilia in patients of group (1), haemoglobin level was significantly reduced in patients of group (1, 2, 3, & 6), serum albumin was significantly reduced in group (2). The percentage of positivity of skin testing using purified protein derivative, ranged between 10% of patients with LHSS, HBV, HCC and HSS with HBV and/or HCV, 20% of patients with HCV and 25% of patients with EHSS. Percentage of positivity in control group was 100%. The mean diameter of delayed intradermal reaction (2.2 +/- 0.5-6.1 +/- 2.1 mms.) was significantly lower in patients than controls. The response of lymphocyte transformation test to phytohaemmagglutinin was significantly lower in patients when compared to controls. The association of HBV and/or HCV with hepatosplenomegaly was accompanied with a marked depression in cell mediated immune response. Anaemia, hypoalbuminemia and nutritional status of the patients with chronic liver diseases play a major role in the suppression of cell mediated immune response.     

A virulent nonencapsulated Haemophilus influenzae

Nontypeable Haemophilus influenzae strain INT1 was isolated from the blood of a young child with clinical signs of meningitis following acute otitis media. No immunologic or anatomic predisposition of this child for invasive bacterial infection with an unusual organism was documented. Sensitive ELISA proved the absence of intra- or extracellular capsular polysaccharide production by INT1 and Southern blot analysis confirmed the lack of an intact capsulation (cap) gene locus within the chromosome. Nevertheless, INT1 established bacteremia and meningitis in infant and weanling rat models of invasive H. influenzae infection. High-molecular-weight DNA isolated from INT1 was shown to confer an invasive phenotype on transformation of a nonencapsulated, avirulent laboratory strain of H. influenzae. Together these findings imply the presence of one or more as-yet-undiscovered, noncapsular virulence factors of H. influenzae that are capable of mediating invasive disease and resistance to immunologic clearance.     

Uptake of the food-derived heterocyclic amine carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine and its N-hydroxy metabolite into rat pancreatic acini and hepatocytes in vitro

Sinc DNA adducts of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) are formed at relatively high levels in the rat pancreas but not liver, we examined the uptake of PhIP and its N-hydroxy metabolite (N-OH-PhIP) into pancreatic acini and hepatocytes to determine if differential tissue uptake was a factor modulating the formation of PhIP-DNA adducts. In addition, since the precursors of PhIP formation are two amino acids and since various amino acid transporters have been identified in the pancreas, the possible involvement of these transporters in the uptake of PhIP and N-OH-PhIP was investigated. The uptake both heterocyclic compounds into both tissue preparations was rapid, with maximal uptake occurring with 1-2 min. However, PhIP uptake into pancreatic acini was significantly (2-way ANOVA, P < 0.05) greater than uptake of N-OH-PhIP into pancreatic acini and the uptake of both PhIP and N-OH-PhIP into hepatocytes. Although uptake was rapid, efflux of both compounds from both tissue preparations was also rapid. However, the efflux rate constant (1.86 +/- 0.6/min, mean +/- SEM) for PhIP) was significantly lower (Student's t-test, P < 0.05) than that for N-OH-PhIP (4.14 +/- 0.04/min) from pancreatic acini. This, combined with the increased uptake of PhIP into pancreatic acini , suggests that there is substantial but reversible binding of PhIP in the pancreas. The uptake of both PhIP and N-OH-PhIP into pancreatic acini and hepatocytes was not affected by the presence of various amino acids in the incubation buffer, indicating that amino acid transporters are not involved in uptake of these compounds. Furthermore, uptake of both compounds did not appear to be dependent on metabolic energy supply. The above data, together with the high octanol:buffer partition coefficients (logP = 1.322 and 1.301 for PhiP and N-OH-PhIP respectively) suggest that both uptake and efflux of PhIP and N-OH-PhIP are consistent with a process of passive diffusion. The tissue binding characteristics for PhIP in the pancreas may create conditions whereby pancreatic cytochrome P450 1A1 can catalyse the formation of N-OH-PhIP. While N-OH-PhIP is not the ultimate reactive DNA binding species, it has been shown to directly bind to and form DNA adducts. Therefore, it is possible that the apparent selective accumulation of PhIP may contribute to the high level of PhIP-DNA adducts formed in the rat pancreas.     

Spiral scanning with anisotropic field of view

Spiral scanning has been used to achieve much shorter scan times than conventional techniques for a wide range of applications. The major drawback with spiral scans is blurring from off-resonant spins, which is proportional to the readout time. Blurring limits maximal spatial resolution and minimal scan time potentially achievable with spiral scanning. Anisotropic field of view is used in conventional scanning to improve image quality by matching k-space trajectory to object characteristics. Anisotropic field of view improves spatial resolution in spiral scanning without increasing scan time or blurring. The resolution improvement results from increased maximal k-space radius allowed by the lower field of view. A field of view reduction by a factor of 2 in one direction provides up to 60% resolution improvement in that direction. Reduced SNR also results from non-uniform k-space sampling.     

The Helicobacter pylori fatty acid cis-9,10-methyleneoctadecanoic acid stimulates protein kinase C and increases DNA synthesis of gastric HM02 cells

Protein kinase C (PKC) has been implicated in the control of epithelial proliferative activity and in the process of malignant transformation. Helicobacter pylori (H.p.) infection is associated with increased gastric epithelial cell proliferation and has been linked with gastric carcinoma. In the present study, we report that the H.p. fatty acid cis-9,10-methyleneoctadecanoic acid (MOA) directly activates PKC (Ka 3.3 microM). The effect of MOA upon PKC activation was Ca2+ dependent but did not require phosphatidylserine as phospholipid cofactor. MOA increased the stimulatory effect of phosphatidylserine at low Ca2+ (1 microM) concentrations. These findings indicate that MOA interacts at the phospholipid- and the diacylglycerol-binding domain to elicit PKC activation. Treatment of gastric mucous cells HM02 caused translocation of PKC from the cytosol to the nuclear, mitochondrial and membrane fraction. Furthermore, MOA stimulated [3H]thymidine incorporation into the DNA of HM02 cells. Our results show that the H.p. fatty acid MOA activates PKC and increases DNA synthesis in gastric epithelial cells.     

Context-dependent nature of destabilizing mutations on the stability of FKBP12

The context-dependent nature in which mutations affect protein stability was investigated using the FK506-binding protein, FKBP12. Thirty-four mutations were made at sites throughout the protein, including residues located in the hydrophobic core, the beta-sheet, and the solvent-exposed face of the alpha-helix. Urea-induced denaturation experiments were used to measure the change in stability of the mutants relative to that of the wild type (Delta DeltaGU-F). The results clearly show that the extent of destabilization, or stabilization, is highly context-dependent. Correlations were sought in order to link Delta DeltaGU-F to various structural parameters. The strongest correlation found was between Delta DeltaGU-F and N, the number of methyl(ene) groups within a 6 A radius of the group(s) deleted. For mutations of buried hydrophobic residues, a correlation coefficient of 0.73 (n = 16,where n is the number of points) was obtained. This increased to 0.81 (n = 24) on inclusion of mutations of partially buried hydrophobic residues. These data could be superimposed on data obtained for other proteins for which similarly detailed studies have been performed. Thus, the contribution to stability from hydrophobic side chains, independent of the extent to which a side chain is buried, can be estimated quantitatively using N. This correlation appears to be a general feature of all globular proteins. The effect on stability of mutating polar and charged residues in the alpha-helix and beta-sheet was also found to be highly context-dependent. Previous experimental and statistical studies have shown that specific side chains can stabilize the N-caps of alpha-helices in proteins. Substitutions of Ile56 to Thr and Asp at the N-cap of the alpha-helix of FKBP12, however, were found to be highly destabilizing. Thus, the intrinsic propensities of an amino acid for a particular element of secondary structure can easily be outweighed by tertiary packing factors. This study highlights the importance of packing density in determining the contribution of a residue to protein stability. This is the most important factor that should be taken into consideration in protein design.