Conformation-dependent antibody response to Pseudomonas aeruginosa outer membrane proteins induced by immunization in humans

Outer membrane proteins (OMPs) of pathogenic bacteria have been used as protective antigens in developing bacterial vaccines. In the present study, we compared the antibody responses to a Pseudomonas aeruginosa OMP vaccine elicited in humans and rabbits by immunization. Immunization with the vaccine induced high titers of serum IgG antibody both in rabbits and humans but reactivities of the induced antibodies with the OMPs were different. The rabbit immune sera recognized most of the OMPs in the vaccine both in immunoblot and immunoprecipitation analyses. In contrast, a great variation in band pattern and intensity was observed among the human immune sera in immunoblot analysis, but not in immunoprecipitation analysis. Denaturation of the OMPs did not affect the binding activity of the rabbit immune sera as determined by ELISA, but substantially reduced those of the human immune sera and anti-OMP IgG purified from a pooled normal human plasma. These data suggest that antibody response to P. aeruginosa OMPs elicited by immunization in humans is mainly directed against discontinuous or conformation-dependent epitopes, which should be taken into account in developing vaccines, especially for OMP-derived synthetic peptides.     

Humoral immune response in lactating dairy cows after repeated exposure to human chorionic gonadotropin

Our objective was to determine if repeated exposure of lactating dairy cows to human chorionic gonadotropin (hCG) would induce an antibody (Ab) response against hCG. Cows either received an hCG injection (hCG; n = 24, each given 2000 IU im) or no treatment (CON; n = 22) 18 days after a timed AI (TAI) and 7 days before initiation of Ovsynch for resynchronization of ovulation and TAI. A subgroup of cows continued in the experiment to receive a second hCG injection (n = 17) 35 days after the first exposure to hCG, whereas another subgroup served as controls (n = 9). Another subgroup of cows continued in the experiment to receive a third hCG injection (n = 11) 35 days after the second exposure to hCG, whereas cows not receiving hCG served as controls (n = 8). A binding radioimmunoassay was used to detect hCG antibodies in serum samples collected 0, 7, 14, 21, and 28 days after treatment. A positive Ab response (>6.2% bound) was defined as three standard deviations above CON binding. No cows had hCG antibodies at Day 0 before the first exposure to hCG. After the first hCG treatment, there was no difference (P = 0.52) between Ab positive cows in CON (0%) and hCG (4%) treatments. At the second hCG treatment, on Day 0 there was no difference (P = 0.65) between CON (0%) and hCG (6%) cows, whereas, more (P = 0.02) hCG cows (47%) were positive than CON cows (0%) within 28 days of the hCG injection. At the third hCG injection, hCG cows tended (P = 0.09) to have a greater percentage of Ab positive (36%) than CON cows (0%), whereas after the injection, a greater (P < 0.01) percentage of hCG cows were positive (hCG = 73% vs. CON = 0%). After the second and third exposure to hCG, 8 of 17 and 8 of 11 cows within the hCG group had greater percent Ab bound at 7, 14, 21, and 28 days after hCG than cows in CON and those with no Ab response. The greatest percent Ab binding occurred at 14 days after the second and third hCG exposure. We concluded that some but not all lactating dairy cows developed an Ab response after repeated exposure to hCG and that maximum response occurred within 14 days after hCG exposure.     

Construction of a recombinant BHV-1 expressing the VP1 gene of foot and mouth disease virus and its immunogenicity in a rabbit model

Foot-and-mouth disease (FMD) and infectious bovine rhinotracheitis (IBR) are two important infectious diseases of cattle. Using bovine herpesvirus type 1 (BHV-1) as a gene delivery vector for development of live-viral vaccines has gained widespread interest. In this study, a recombinant BHV-1 was constructed by inserting the synthetic FMDV (O/China/99) VP1 gene in the the gE locus of BHV-1 genome under the control of immediately early gene promoter of human cytomegalovirus (phIE CMV) and bovine growth hormone polyadenylation (BGH polyA) signal. After homologous recombination and plaque purification, a recombinant virus named BHV-1/gE⁻/VP1 was acquired and identified. The immunogenicity was confirmed in a rabbit model by virus neutralization test and enzyme-linked immunosorbent assay (ELISA). The result indicated that the BHV-1/gE⁻/VP1 has the potential for being developed as a bivalent vaccine for FMD and IBR.     

Doubly robust estimates for binary longitudinal data analysis with missing response and missing covariates

Longitudinal studies often feature incomplete response and covariate data. Likelihood-based methods such as the expectation-maximization algorithm give consistent estimators for model parameters when data are missing at random (MAR) provided that the response model and the missing covariate model are correctly specified; however, we do not need to specify the missing data mechanism. An alternative method is the weighted estimating equation, which gives consistent estimators if the missing data and response models are correctly specified; however, we do not need to specify the distribution of the covariates that have missing values. In this article, we develop a doubly robust estimation method for longitudinal data with missing response and missing covariate when data are MAR. This method is appealing in that it can provide consistent estimators if either the missing data model or the missing covariate model is correctly specified. Simulation studies demonstrate that this method performs well in a variety of situations.     

Intrinsic pKas of ionizable residues in proteins: An explicit solvent calculation for lysozyme

Molecular dynamics simulations of triclinic hen egg white lysozyme in aqueous solution were performed to calculate the intrinsic pK_as of 14 ionizable residues. An all-atom model was used for both solvent and solute, and a single 180 ps simulation in conjunction with a Gaussian fluctuation analysis method was used. An advantage of the Gaussian fluctuation method is that it only requires a single simulation of the system in a reference state to calculate all the pK_as in the protein, in contrast to multiple simulations for the free energy perturbation method. pK_int shifts with respect to reference titratable residues were evaluated and compared to results obtained using a finite difference Poisson-Boltzmann (FDPB) method with a continuum solvent model; overall agreement with the direction of the shifts was generally observed, though the magnitude of the shifts was typically larger with the explicit solvent model. The contribution of the first solvation shell to the total charging free energies of the titratable groups was explicitly evaluated and found to be significant. Dielectric shielding between pairs of titratable groups was examined and found to be smaller than expected. The effect of the approximations used to treat the long-range interactions on the pK_int shifts is discussed. © 1994 Wiley-Liss, Inc.     

How predator functional responses and Allee effects in prey affect the paradox of enrichment and population collapses

In Rosenzweig-MacArthur models of predator-prey dynamics, Allee effects in prey usually destabilize interior equilibria and can suppress or enhance limit cycles typical of the paradox of enrichment. We re-evaluate these conclusions through a complete classification of a wide range of Allee effects in prey and predator's functional response shapes. We show that abrupt and deterministic system collapses not preceded by fluctuating predator-prey dynamics occur for sufficiently steep type III functional responses and strong Allee effects (with unstable lower equilibrium in prey dynamics). This phenomenon arises as type III functional responses greatly reduce cyclic dynamics and strong Allee effects promote deterministic collapses. These collapses occur with decreasing predator mortality and/or increasing susceptibility of the prey to fall below the threshold Allee density (e.g. due to increased carrying capacity or the Allee threshold itself). On the other hand, weak Allee effects (without unstable equilibrium in prey dynamics) enlarge the range of carrying capacities for which the cycles occur if predators exhibit decelerating functional responses. We discuss the results in the light of conservation strategies, eradication of alien species, and successful introduction of biocontrol agents.