Thermodynamics of Electrolytes on Anisotropic Lattices

The phase behavior of ionic fluids on simple cubic and tetragonal (anisotropic) lattices has been studied by grand canonical Monte Carlo simulations. Systems with both the true lattice Coulombic potential and continuous-space $1/r$ electrostatic interactions have been investigated. At all degrees of anisotropy, only coexistence between a disordered low-density phase and an ordered high-density phase with the structure similar to ionic crystal was found, in contrast to recent theoretical predictions. Tricritical parameters were determined to be monotonously increasing functions of anisotropy parameters which is consistent with theoretical calculations based on the Debye-H\"uckel approach. At large anisotropies a two-dimensional-like behavior is observed, from which we estimated the dimensionless tricritical temperature and density for the two-dimensional square lattice electrolyte to be $T^*_{tri}=0.14$ and $\rho^*_{tri} = 0.70$.Comment: submitted to PR

Engagement of different Fc-gamma receptors in phagocytosis of immune complexes containing antibodies to mutated human chorionic gonadotropin β chain (hCG-beta) and native hCG molecule

The aim of this study was to investigate the role of Fcγ receprors (FcγR) in vitro, in phagocytosis of hormone-antibody complexes formed after immunization with the mutant hCGβ(R68E). Native, FITC labeled hCG was added to the sera from mutant hCGβ(R68E) immunized rabbits. The suspensions of phagocytic cells were selectively incubated with monoclonal antibodies to FcγRI, FcγRII, FcγRIII and the complement receptor 3 in order to block their functions and phagocytosis was visualized by flow cytometry. We show that the phagocytosis of immune complexes containing anti-hCGβ(R68E) sera of rabbits and native hCG molecules by monocytes and neutrophils is mediated by FcγRI(CD64) and FcγRIII(CD16) respectively in cooperation with the complement receptor 3 (CR3)

Elimination of luteinizing hormone cross-reactive epitopes from human chorionic gonadotropin.

The β-chain of human chorionic gonadotropin (hCG) has been shown to have efficacy in clinical trials when used as a contraceptive vaccine. This hormone is a heterodimer, the α-chain being shared with the other members of the glycoprotein hormone family but the β-chain being unique to hCG. Nevertheless, there is sequence homology between the hCG β-chain and the β-chain of human luteinizing hormone (hLH) which results in cross-reactive antibodies being produced following immunization with wild-type hCGβ. To reduce or eliminate such cross-reactions we generated a number of mutants of the hCGβ-chain. One mutant (hCGβ(R68E)), containing an arginine to glutamic acid replacement at position 68, has been expressed as a recombinant protein in High Five™ insect cells. The recombinant BAChCGβ(R68E) form of this molecule was used to immunize rabbits and the antibody response compared to the response following immunization with the recombinant wild-type protein BAChCGβ and with the native hCGαβ heterodimer isolated from pregnancy urine. The mutant elicited the production of antibodies which avidly recognize native hCG. Compared to immunization with wild-type hCG, the response showed very little cross reactivity with hLH. This is demonstrated to be due to a radically altered epitope usage in the response to the mutant, which now focuses mainly upon the C-terminal region of the β-chain

Refocusing of B-cell responses following a single amino acid substitution in an antigen.

Intranasal immunization of BALB/c strain mice was carried out using baculovirus-derived human chorionic gonadotrophin (hCG) β-chain, together with Escherichia coli heat-labile enterotoxin. Gonadotrophin-reactive immunoglobulin A (IgA) was induced in a remote mucosal site, the lung, in addition to a systemic IgG response. The extensive sequence homology with luteinizing hormone (LH) results in the production of LH cross-reactive antibodies when holo-hCG is used as an immunogen. In contrast to wild-type hCGβ, a mutated hCGβ-chain containing an arginine to glutamic acid substitution at position 68 did not induce the production of antibodies which cross-react with LH. Furthermore, the epitopes utilized in the B-cell response to the mutated hCGβ shifted away from the immunodominant region of the parent wild-type molecule towards epitopes within the normally weakly immunogenic C terminus. This shift in epitope usage was also seen following intramuscular immunization of rabbits. Thus, a single amino acid change, which does not disrupt the overall structure of the molecule, refocuses the immune response away from a disadvantageous cross-reactive epitope region and towards a normally weakly immunogenic but antigen-unique area. Similar mutational strategies for epitope-refocusing may be applicable to other vaccine candidate molecules