Cytophilic Properties Research Articles

Direct Evidence of Polar Ordering and Investigation on Cytophilic Properties of Pyroelectrified Polymer Films by Optical Second Harmonic Generation Analysis

Pyroelectrification (PE) has been proposed as a low-cost electrode-free tool for orienting and aligning dipole molecules in polymer layers, by means of the electric field produced by a pyroelectric crystal under appropriate thermal stimulations. Probing and assessing the coherent polarization arrangement is of fundamental importance for the process control and optimization but is also a challenging task. In fact, the probing operation must be noninvasive and avoid any disarrangement the dipoles and thus without interfering with the resulting surface charges. Here we show that the PE-induced polar ordering can be probed in situ by an electrode-free analysis based on the measurement of the intensity of the second-harmonic optical wave generated by the polymer film. In fact, the results show a substantial enhancement of the second-order susceptibility of the polymer layer, caused by the PE-induced dipoles alignment. Moreover, thanks to this approach, it is demonstrated the ability of PE process to polarize p...

The humoral response to Plasmodium falciparum VarO rosetting variant and its association with protection against malaria in Beninese children

BackgroundThe capacity of Plasmodium falciparum-infected erythrocytes to bind uninfected erythrocytes (rosetting) is associated with severe malaria in African children. Rosetting is mediated by a subset of the variant surface antigens PfEMP1 targeted by protective antibody responses. Analysis of the response to rosette-forming parasites and their PfEMP1 adhesive domains is essential for understanding the acquisition of protection against severe malaria. To this end, the antibody response to a rosetting variant was analysed in children recruited with severe or uncomplicated malaria or asymptomatic P. falciparum infection.MethodsSerum was collected from Beninese children with severe malaria, uncomplicated malaria or P. falciparum asymptomatic infection (N = 65, 37 and 52, respectively) and from immune adults (N = 30) living in the area. Infected erythrocyte surface-reactive IgG, rosette disrupting antibodies and IgG to the parasite crude extract were analysed using the single variant Palo Alto VarO-infected line. IgG, IgG1 and IgG3 to PfEMP1-varO-derived NTS-DBL1α1, CIDRγ and DBL2βC2 recombinant domains were analysed by ELISA. Antibody responses were compared in the clinical groups. Stability of the response was studied using a blood sampling collected 14 months later from asymptomatic children.ResultsSeroprevalence of erythrocyte surface-reactive IgG was high in adults (100%) and asymptomatic children (92.3%) but low in children with severe or uncomplicated malaria (26.1% and 37.8%, respectively). The IgG, IgG1 and IgG3 antibody responses to the varO-derived PfEMP1 domains were significantly higher in asymptomatic children than in children with clinical malaria in a multivariate analysis correcting for age and parasite density at enrolment. They were essentially stable, although levels tended to decrease with time. VarO-surface reactivity correlated positively with IgG reactivity to the rosetting domain varO-NTS-DBL1α1. None of the children sera, including those with surface-reactive antibodies possessed anti-VarO-rosetting activity, and few adults had rosette-disrupting antibodies.ConclusionsChildren with severe and uncomplicated malaria had similar responses. The higher prevalence and level of VarO-reactive antibodies in asymptomatic children compared to children with malaria is consistent with a protective role for anti-VarO antibodies against clinical falciparum malaria. The mechanism of such protection seems independent of rosette-disruption, suggesting that the cytophilic properties of antibodies come into play.

Synthesis and characterization of biocompatible, degradable, light‐curable, polyurethane‐based elastic hydrogels

A series of degradable polyurethane-based light-curable elastic hydrogels were synthesized from polycaprolactone diol, polyethylene glycol (PEG), lysine diisocyanate (LDI), and 2-hydroxyethyl methacrylate (HEMA) through UV light initiated polymerization reaction. LDI was used as hard segment and polycaprolactone (PCL) and/or PEG were used as soft segments. By changing the PCL to PEG ratio during the prepolymer synthesis, polyurethanes with different soft segmental structures, hydrophilicity, and cytophilicity were obtained after light-initiated polymerization. The chemical structures of the synthesized polymers were characterized using differential scanning calorimetry and Fourier transform infrared spectroscopy. Physical properties such as swelling, mechanical properties, and in vitro degradation were evaluated. Materials containing a higher ratio of PEG exhibit higher water absorbance, higher degradation rate in vitro, and lower mechanical strength in the hydrated state. Mouse embryonal carcinoma-derived clonal chondrocytes were used as a model cell type to study the cytocompatibility of the synthesized polymers. Chondrocyte attachment, proliferation rates, and morphologies varied with changes in the PCL/PEG ratio. With a higher PEG ratio, lower cell attachment and proliferation were observed. To improve the cell attachment and proliferation on high PEG content hydrogels, bioactive molecules, such as peptides and proteins, were conjugated or immobilized in the gel matrix during the light-curing process. In this study, a short peptide, Arg-Gly-Asp-Ser, was used as a model biomolecule and incorporated into the gels during the light-curing process and improved cell growth was observed. In summary, the use of PCL/PEG at different ratios, as well as the introduction of HEMA into polyurethane, allows the synthesis of a series of biocompatible elastic hydrogels with tunable physical and cytophilic properties through light-initiated polymerization. This series of materials also allows for controlling cell attachment and growth by incorporating bioactive molecules during the light-curing process.

Cytophilic immunoglobulins revisited via natural killer cells.

Cytophilia is one of the biologic properties of the Fc region of immunoglobulins operationally defined as the ability of an antibody molecule to attach to certain cell types before combination with antigen. By attachment of cytophilic antibody to membrane Fc receptors, cells become "armed" with antibodies and able to interact specifically with soluble or particulate antigens. In contrast to this cytophilia, the so-called opsonic antibody binds to FcR of various cell types only after it has complexed with antigen. In spite of knowledge of cytophilic properties of immunoglobulins for more than 30 years and an impressive accumulation of facts regarding the structure and function of cell-surface FcR binding IgG, IgE, or IgA molecules, less progress has been made in understanding the molecular basis of cytophilia. Our extensive studies of the structural and functional aspects of the interaction of IgG in monomeric form with human natural killer cells, via the type IIIA IgG Fc receptor (Fc gamma RIIIA), provide a focal point for revisiting this major pathway of direct and continuous communication between the humoral and cellular compartments of the immune system.

Identification of the Fc gamma receptor class I binding site in human IgG through the use of recombinant IgG1/IgG2 hybrid and point-mutated antibodies.

To characterize the region on human IgG1 responsible for its high-affinity interaction with the human Fc gamma receptor class I (Fc gamma RI), we have analyzed the binding properties of a series of genetically engineered chimeric antidinitrophenyl antibodies with identical murine antibody combining sites and hybrid IgG1/IgG2 human constant (C) regions. In addition, we have investigated a panel of reciprocally point-mutated IgG1 and IgG2 chimeric antibodies to identify the amino acid residues that confer cytophilic properties to human IgG1. Our data unambiguously indicate that cytophilic activity of IgG1 is an intrinsic property of its heavy-chain C region 2 (CH2) domain. We report that the entire sequence spanning residues 234-237 (LLGG) is required to restore full binding activity to IgG2 and IgG4 and that individual amino acid substitutions failed to render IgG2 active. Nevertheless, the reciprocal single point mutations in IgG1 either significantly lowered its activity or abolished it completely. Finally, we observed that an IgG2 antibody containing the entire ELLGGP sequence (residues 233-238) was more active than wild-type IgG1. This finding suggests that in addition to the primary contact site identified in the N terminus of the gamma 1 CH2 domain, secondary sites involving residues from the C-terminal half of the domain may also contribute to the IgG1-Fc gamma RI interaction.

Immunoglobulins of colostrum—VI. comparative studies of cytophilic properties of bovine serum and colostral IgG

In our previous studies, using physical-chemical and serological methods, substantial differences between bovine serum and colostral IgG, especially IgG2, have been shown. The structural differences were localized in the Fc region of immunoglobulins studied. The present comparative studies were undertaken to determine whether structural differences in the Fc region of bovine serum and colostral IgG are reflected in the interaction of these immunoglobulins with the guinea-pig peritoneal macrophage Fc γ receptor. It was found that binding of bovine serum and colostral IgG1 was a saturable process and only quantitative differences in the mode of binding to the Fc receptor were observed. There is, however, a big difference in cytophilic activity of bovine IgG2—no saturable and reversible binding is observed in the case of bovine serum IgG2.

Immunogenicity and effector functions of glutaraldehyde-treated rabbit and mouse immunoglobulin G

Rabbit and mouse IgG treated with glutaraldehyde (GA) were immunogenic in homologous species. Glutaraldehyde treatment induced in the IgG molecule two types of antigenic determinants. One of them was found on the monomeric fraction of GA-treated rabbit IgG (haptenic determinant) and the other on the polymeric fraction (structural determinant). The haptenic determinants were found also on monoaldehyde-treated rabbit IgG and GA-treated Fab and Fc fragments. It was demonstrated that rabbit and mouse antibodies are specific for GA-treated IgG and have species specificity. While GA treatment did not alter the antigen binding capacity of rabbit IgG antibody, its effector functions (except protein A binding) were much affected. Thus it was found that GA treatment enhances IgG ability to react with rheumatoid factor, reduces drastically its capacity to activate the complement system, abolishes the cytophilic properties of IgG and accelerates its catabolic rate. The possible blocking effect of GA on the amino acid residues (mainly Lys) situated in or very close to the effector sites of the IgG molecule is suggested.

Isolation of a rabbit IgG fraction with cytophilic properties

About 15% of rabbit IgG loaded on a column of Con A-Sepharose 4B was found to be specifically bound to the column due to a structural variation in its carbohydrate moiety. The Con A-retained rabbit IgG contained a higher amount of neutral hexoses than the initial IgG but its molecular weight, antigenic structure and half-life were identical or similar. The Con A-retained rabbit IgG has an affinity for the Fc receptor-bearing homologous macrophages which is 10 times higher than that of the initial IgG. The IgG fraction not retained on Con A-Sepharose is practically devoid of binding ability. These results suggest that the Con A-bound IgG may represent the cytophilic fraction of monomeric IgG responsible for the binding of IgG to Fc receptor-bearing cells.

Studies of rat antibodies specific for myelin basic protein (MBP) antibody-dependent cell-mediated lysis of MBP-sensitized targets in vitro

Rats immunized with rat myelin basic protein (MBP) in an encephalitogenic regimen produce antibodies which cooperate with spleen cells from unimmunized rats in the specific lysis of MBP-sensitized chicken erythrocytes (MBP-CRBC) in vitro. Antibodies against MBP capable of participating in antibody-dependent cell-mediated cytotoxicity (ADCC) were detected in serum 9 days post immunazation, and prior to the onset of experimental allergic encephalomyelitis (EAE). Measurements based on a sensitive radioimmunoassay technique had previously established that anti-MBP activity emerges by day 9, early enough to participate in events leading up to EAE. The ADCC assay was designed to further characterize functions of immunoglobulins associated with the humoral response to MBP, with emphasis on the cytophilic properties of early antibodies. The assay described was found to be nearly as sensitive as the RIA and could detect specific syngeneic rat anti-MBP at concentrations of about 0.03 pmoles/ml serum. Whether ADCC-type reactions take place in the central nervous system during acute EAE is not known; however, the presence of early cytophilic antibody in serum suggests that humoral immunity may play an ancillary role to that demonstrated for T-cell immunity in EAE.

Classes of cell surface immunoglobulins detected on rat lymphocytes by enzymic radioiodination

It was shown by the methods of enzymic radioiodination, immunoprecipitation, and electrophoresis in sodium dodecylsulfate-polyacrylamide gels that splenic lymphocytes of normal rats carry on their surface immunoglobulins of two main classes: monomeric IgM (IgMS) and Ig(H2L2), the heavy chains of which are a little smaller than μ chains and differ from them in their antigenic properties. The class of cell surface Ig thus revealed is evidently equivalent to human IgD and to the IgD-like protein of the cytoplasmic membrane of mouse lymphocytes. The presence of small quantities of IgG on the surface of lymphocytes can be explained both by its cytophilic properties and by the immunological state of the experimental animals.

Cytophilic properties of IgA to human neutrophils.

In 1961 Boyden and Sorkin demonstrated that antigens can be bound to spleen cells which have previously been incubated with specific antisera (1). The term “cytophilic” immunoglobulins was coined for this type of antibody. Subsequently, it was shown that immunoglobulins attach via the Fc fragment to receptors on phagocytic cells such as macrophages (2,3), monocytes (4) and neutrophils (5). The biological importance of the cytophilic antibodies appears to be promotion of phagocytosis (opsonization) of antigens. Not all immunoglobulins are cytophilic. In rodents, IgG of slow electrophoretic mobility, γ2G, is cytophilic whereas γ1G, the anodally migrating IgG is not (3). In man, it has been shown by inhibition studies that IgG1 and IgG3 are cytophilic for monocytes (4) and neutrophils (5). Most of these findings were made by studying “rosette” formation, that is the adherence of antibody coated red cells to phagocytes (3,4,5). More recently, cytophilic properties have also been studied by measuring the uptake of radiolabeled immunoglobulins on macrophages (6) or by release of histamine from basophils (7). Relatively little is known about cytophilic properties of IgA, probably because it is difficult to obtain pure IgA antibodies suitable for cytophilic testing. Since the cytophilic reaction depends on the Fc fragment, immunoglobulins having no demonstrated antibody activity such as myeloma proteins can also be used as a source of IgA. Isolated IgA myeloma proteins were therefore used in this study. First, the release of lysosomal enzymes from neutrophils following incubation with aggregated IgA was analyzed (8) and second, the uptake of radiolabeled IgA onto neutrophils was measured and compared to that of other immunoglobulin classes (9).

The immunologic response to plasmodium.

Summary and ConclusionsThe species and strain specificity which characterizes acquired immunity to many malarial infections indicates that specific antibody plays a primary role in the response. The importance of serum antibody has been established by passive transfer tests in man and experimental animals. Immune serum has also been shown to inhibit the cyclical growth of P. knowlesi maintained in vitro. Studies on this system have revealed that immune serum has no effect upon the growth of intracellular parasites, but acts upon mature schizonts or free merozoites to inhibit the cycle of growth that follows schizogony. The inhibitory antibodies appear to be distinct from the schizont agglutinins present in immune sera and are associated with IgG and IgM, but not with IgA or IgE; their action is species-specific, but not complement-dependent and requires at least two combining sites per antibody molecule. The similarity between protective malarial antibody and some viral neutralizing antibodies is apparent from these experiments. Claims that cell-mediated immunity (i.e., a reaction mediated by sensitized lymphocytes of thymic origin, such as those responsible for graft rejection) play an effector role in malarial immunity are at present based upon inconclusive evidence.Although serum antibody appears to play a primary role in acquired malarial immunity its clinical effectiveness may be dependent upon a synergistic action with the macrophage system. Malarial antibody is present in two Ig classes (IgG and IgM) which are known to have cytophilic properties and can therefore promote phagocytosis of antibody-bound antigen. The phagocytic activity of macrophages during malarial infection has long been recognized on morphological grounds and the role of specific antibody in promoting macrophage ingestion of parasites has been demonstrated in vitro. The importance of a primed macrophage system in malarial immunity may explain certain discrepant results observed in passive immunization experiments. Thus, although immune IgG produced a rapid elimination of parasites in West African children with severe infections, equivalent doses of immune rhesus IgG did not consistently inhibit parasitemia in normal monkeys challenged with only 50 P. knowlesi parasites.The mechanisms which lead to the state of “premunition,” i.e., clinical immunity associated with continued low-grade infection, have long been a subject of speculation. This characteristic response could be attributable to relatively poor immunogenicity of the plasmodium, the immuno supressive effect of malarial infection, the presence of enhancing antibody, or the occurrence of antigenic variation. Available facts indicate that antigenic variation in P. knowlesi is fundamental for parasite survival in the immunized host and constitutes the basic mechanism which underlies chronicity of infection. In vitro assays have shown that protective antibody is predominantly specific for those variants which have produced patent infections. However, antibody against other variants is also present at lower titer and is associated with clinical immunity on challenge with such variants. This explains why P. knowlesi parasites which arise by antigenic variation during the course of chronic infection produce mild parasitemia in the host and yet are fully virulent in normal monkeys.The state of “sterilizing” immunity, such as follows P. berghei infections in rats, has not been studied in detail. It is clearly a matter of interest and importance to elucidate the nature of the immune response in such infections and to establish the features which distinguish it from the less effective, “non-sterilizing” responses characteristic of many monkey and human malarias.

Sedimentation Properties of Antibody Cytophilic for Macrophages

Summary 7 S and 19 S fractions of rabbit and mouse antisera were tested for cytophilic properties for homologous macrophages. This activity was found only in the 7 S fractions.