Search

X-ray crystal structures of IgG-Fc provide evidence of extensive noncovalent interactions between the protein and carbohydrate moieties, and glycosylation, at Asn-297 within the Fc, has been shown to be important for effector functions mediated through Fc gamma receptors expressed on leukocytes. We have applied protein engineering in an attempt to define protein/carbohydrate interactions essential to wild-type biological activity. We demonstrate that replacement of Lys-246, Asp-249, and Glu-258, which make contacts with GlcNac and Gal on the outer alpha[1-->6] arm, do not affect recognition of human chimeric IgG3 by human Fc gamma RI and Fc gamma RII. However, replacement of Asp-265, which make contacts with the primary GlcNac sugar residue and is covalently attached to Asn-297, resulted in loss of recognition of both Fc gamma RI and Fc gamma RII. Similarly, replacement of Asp-265 in mouse IgG2b resulted in loss of recognition by mouse Fc gamma RII. These results suggest that noncovalent contacts of Asp-265 with the primary GlcNac residue are important for maintenance of recognition of IgG by Fc gamma receptors whereas contacts with GlcNac and Gal on the alpha [1-->6] arm do not have a measurable effect. This conclusion was supported by experiments in which galactose-deficient and fully galactosylated forms of a human IgG4-Fc fragment were shown to be equivalent in their ability to inhibit superoxide generation by IgG4 stimulated U937 cells.

In order to mount an effective antibody response to soluble and certain other types of antigens, B cells need help from T cells. Recently, an important receptor-ligand pair has been identified as essential for successful cognate interaction between these two classes of lymphocytes. CD40 was first identified as a receptor-like molecule on B cells which when ligated by antibody could deliver signals to prime for growth, differentiation, or survival. Later its counterstructure--termed CD40 ligand (CD40L)--was discovered to be an inducible type II glycoprotein of helper T cells. In this review, the central role of the CD40-CD40L interaction in the various phases of the B cell response to T-dependent antigens is discussed drawing from both in vitro and in vivo studies.

Secondary systemic immune responses are predominantly of the IgG class and passive administration of intravenous IgG, from pooled normal serum, is an effective prophylactic and/or therapeutic treatment for patients with defined immunodeficiencies. However, the proportions of each IgG subclass present within a specific antibody response may differ dramatically from that of the total IgG pool. For some antigens the response may be essentially restricted to a single subclass and it may be presumed that the antibody isotype produced has an optimal protective role. The clinical consequences of selective IgG subclass deficiency appears to validate this presumption. In this review we emphasize the differences in effector functions activated by the IgG subclasses and hence the mechanisms responsible for the removal and destruction of antigen/antibody complexes. These studies are relevant to diagnosis and treatment of patients with recurrent infection; the IgG isotype of monoclonal antibodies selected for passive in vivo therapy; the generation of customized antibodies having a pre-determined profile of effector functions and 'immuno-direction' with new vaccines to provoke an antibody response having an isotype profile optimal for the proposed application.

Cross-linking of surface Ig (sIg) on resting B cells can generate intracellular signals; however, for T-dependent antigens to promote growth and differentiation additional surface receptors must be engaged. Ligation of CD40 can stimulate B cell proliferation in the presence of interleukin-4. A recently identified counterstructure for CD40 is found on T helper cells and is believed to represent the cognate ligand for B cell activation. This study investigates the role of CD40 as an accessory molecule in sIg-dependent B cell activation. Simultaneous ligation of sIg and CD40 by monoclonal antibodies (mAb) in the presence of mouse L cells which express human Fc gamma receptor type II (Fc gamma RII-L cells) results in potent stimulation of small resting B cells. When CD40 is co-ligated, picomolar concentrations of mouse IgG1 anti-mu, and anti-delta mAb can stimulate B cell proliferation. This requires interaction of the anti-Ig mAb with the Fc gamma RII-L cells: a mouse IgG2a anti-mu mAb which is not recognized by Fc gamma RII, was > or = 1000-fold less effective. These findings suggest a mechanism for B cell activation whereby engagement of T cells via CD40 and its cognate ligand provides potent enhancement of signals delivered through sIg. Based on these observations, models for the activation of B cells by T-dependent antigens are presented.

Thirty-nine girls aged 6 to 12 participated in this study, each having been referred for evaluation of suspected child sexual abuse. The study investigated the prevalence of depression in the sample as well as the relationship of depressive symptoms to severity of abuse and potential mediator variables. The Child Behaviour Checklist and Child Depression Inventory were used to asses the severity of depression. A composite score for severity of abuse was derived from child disclosure and medical findings. Results indicated that 67% of the children could be classified as experiencing symptoms consistent with a diagnosis of depression. Severity of abuse was not significantly correlated with depression intensity scores. Stepwise regression analyses revealed that a high number of stressful life events and low IQ were significant predictors of depression scores. The clinical implications of these findings are discussed.

This study investigates the role played by Fc gamma RI and Fc gamma RII in triggering the respiratory burst induced in human monocyte-like U937 cells by monoclonal chimaeric anti-NIP antibodies expressing the human IgG subclass and mouse IgG2b heavy chains. Respiratory burst activity was measured as superoxide generation. Four separate lines of evidence indicate a predominant role for Fc gamma RI in triggering superoxide generation induced by erythrocytes sensitized with up to the maximum of 100,000 IgG molecules per cell. Firstly, erythrocytes sensitized with mouse IgG2b anti-NIP antibodies which are not recognized by human Fc gamma RI, did not induce a response but when residue Glu-235 was replaced by Leu to give the lower hinge sequence of mouse IgG2a which is recognized by Fc gamma RI, the mutant bound to Fc gamma RI and induced a response equal to 80% of that given by chimaeric human IgG3. Chimaeric human IgG3 antibodies with amino acid substitutions in the lower hinge showed reduced activity and the greatest reductions (< 32% of wild type antibody activity) were associated with changes at Leu-235 which is critical for recognition by Fc gamma RI. Secondly, chimaeric human IgG4 antibodies which are not recognized by Fc gamma RII, were able to induce superoxide generation. The rank order of abilities of chimaeric human IgG subclass antibodies to induce responses was IgG3 > IgG1 > IgG4 > > IgG2. Thirdly, responses induced by chimaeric human IgG were inhibited by concns of monomeric human IgG3 in the nM range. Finally, chimaeric human IgG3 induced responses were inhibited by anti-Fc gamma RI, but not anti-Fc gamma RII monoclonal antibodies. Consistent with a major role for Fc gamma RI in triggering the responses of U937 cells, erythrocytes sensitized with chimaeric human IgG3 did not induce superoxide generation by neutrophils which express Fc gamma RII and Fc gamma RIII, or eosinophils which express Fc gamma RII, but neither of which expresses Fc gamma RI.

In the 1990s, politics will replace takeovers as the defining tool for corporate governance challenges, and a marketplace of ideas will replace the frenzied activity that once dominated the financial marketplace in the 1980s. In the transaction-driven market of the past, corporate raiders used junk bonds and other financial tools to take control of their targets. In the new marketplace of ideas, debate will replace debt as active shareholders press specific operating policies for their target corporations in a new politicized market for corporate control. John Pound, associate professor of public policy at the John F. Kennedy School of Government at Harvard, reports that investors are already using shadow management committees, independent director slates, and outside experts to influence management policy. Pound cites Carl Icahn's battle for control of USX as an example of the emerging trend. What began as a hostile takeover ended with a negotiated solution in which many constituencies ultimately played a role in the restructuring of the company. This political approach to governance gives management a chance to embrace a bargain that is in its long-term interest. By promoting politically based tactics, managers can generate political capital with their major investors. Managers in companies as diverse as Avon and Lockheed now meet regularly with investors, seeking their input on both financial and strategic decisions. In the new politicized market for corporate control, striking a bargain with long-term investors is ultimately in the best interest of the corporation.

Important mammalian defensive functions such as phagocytosis are triggered in leukocytes by the interaction of the Fc region of IgG with cell surface receptors (Fc gamma R). The CH2 domain of IgG has been implicated previously as the site of interaction with human and mouse Fc gamma R. This domain was mapped for interaction with mouse Fc gamma R11 expressed by the macrophage-like cell line P388D1, using two panels of a total of 32 site-directed mutants of mouse IgG2b and chimeric human IgG3 monoclonal antibodies. Two potential binding sites have been identified: one in or within the vicinity of the lower hinge site on IgG for human Fc gamma R1, and one within the binding site on IgG for Clq. The three mutant IgGs (Gly 237----Ala, Asn 297----Ala, and Glu 318----Ala) which do not interact in complexed form also fail to bind as monomers. A 1H NMR study of the three non-binding monomeric mutants suggests that the mutations are largely site-specific, indicating that IgG interacts with mouse Fc gamma R11 at two regions within the CH2 domain. This interaction dictates phagocytosis mediated by Fc gamma R11 of the P388D1 cell line.

Evidence from several experimental approaches allows us to conclude that the primary amino acid sequence of the lower hinge region (residues 234-237) of human IgG molecules determines recognition by human Fc gamma RI, Fc gamma RII and Fc gamma RIII. Glycosylation of the CH2 domain is also essential, although the carbohydrate is not accessible for direct interaction with ligands. The role of the carbohydrate moiety may be to maintain a protein conformation that allows accessibility to amino acid side chains essential for ligand recognition and binding. It appears logical that the evolutionarily-related Fc gamma R molecules should interact with overlapping non-identical sites on the IgG molecule.

Fractionation of mononuclear cells from human fetal liver provides a cell population at early stages of myeloid differentiation which, when cultured, generates neutrophils and macrophages for up to a month. These studies describe the further purification of an undifferentiated myeloid blast cell population by rosette sedimentation of unwanted cells, after coating these cells with monoclonal antibodies which identify macrophages and erythroblasts. In culture, the purified blast cells generated only neutrophils and macrophages. When treated with 10 nM PMA, 62% of the purified cells were induced to differentiate towards macrophages within 48 h. PMA-induced cells acquired morphological features of macrophages and synthesized alpha-naphthyl acetate esterase. The differentiation of the remaining blast cells towards neutrophils, seen in untreated cultures, was completely inhibited by PMA, as revealed by the absence of increases in the numbers of cells expressing lactoferrin and an antigen which appears at the promyelocyte stage of differentiation. Thus, PMA effects intracellular changes which both promote monopoiesis and inhibit granulopoiesis, suggesting a reciprocal interaction between intracellular processes which regulate the capacity for the two pathways of maturation. The purified blast cell population provides a good model system for studies of molecular events which regulate the expression of macrophage characteristics.

Hemocoelic injection and vaginal insertion of selected male reproductive and non-reproductive tissue homogenates into fed-virgin female Ornithodoros parkeri stimulated varying degrees of ovum maturation and/or oviposition during 14 and 30 day observation periods, respectively. Mean times for oviposition and mean numbers of eggs laid per ovipositing female receiving hemocoelic injections of male reproductive tissue homogenates did not differ significantly from fed-mated controls. In addition, hemocoelic injection of male salivary glandular homogenate induced oviposition, yet synganglial homogenate did not. Although vaginal insertion induced both ovum maturation and oviposition, the effect was not as pronounced as when similar doses were administered by hemocoelic injection. These results indicate that a complex interrelated series of precopulatory and copulatory stimuli are necessary for oviposition to occur in fed O. parkeri.

The male reproductive system consists of paired tests, vasa deferentia and dark-staining lateral accessory glands, single ventromedial spongy accessory gland, seminal vesicle, ejaculatory apparatus, and gonopore. The female system consists of paired rami sacculi, sacculus foemineus, ovary (lyriform and medial portions), oviduct, vagina, and paired vaginal glands.

Protonymphal Dermanyssus gallinae were irradiated with 0.50, 0.75, 1.0, 3.0, and 6.0 krad of gamma radiation and subsequently monitored regarding their developmental, feeding, and mating success. Also, sex ratios of adults treated as protonymphs were recorded as were sex ratios of embryos and F1 adults produced by these adults. Doses up to 1.0 krad did not prevent development of treated protonymphs to the adult stage or stop mating. Three krad reduced the number of treated protonymphs attaining adulthood and 6.0-krad treatment prevented all mites from developing to the adult stage. Egg (embryo) production was normal for mites treated with 0.50 krad, but significantly curtailed by doses of 0.75 krad and greater. Radiation doses used in this study did not appear to affect the normal variable sex ratios observed in untreated mites.

Ovarian dlevelopmnent, vitellogenesis, andt etnbrvogenesis in recently matedlce fiemnales of tlhe sofi tick Ornithodoros parkeri Coolev were prevented by topical application of the insect antiallatotropin precocene 2. ThCe blockage was relieved by topical application of jtivenile hormonoe. Cancellation of the anti-juvenile hormnone jJects of precocene 2 and the reestablishment of oogenesis (and oviposition in one specimen) bv a naturally occurring insect juvenile hormone argues strongly for a physiological role of juvenile hormone in acarine reproduction.

IgG rheumatoid factors (RF) may play an important role in the pathogenesis of rheumatoid arthritis (RA). Our study investigates the relationship between class specific RF levels measured by radioimmunoassay and disease activity in patients with RA undergoing chrysotherapy. Nineteen patients were treated with 20 mg disodium aurothiomalate weekly for 6 months. Rheumatoid disease activity was assessed before and after 6 months' treatment and the level of IgG, IgA and IgM RF measured. There were significant falls in disease activity (p less than 0.005), IgA RF (p less than 0.005) IgG RF (p less than 0.005) and SCAT (p less than 0.025), but not IgM RF, over the 6 month treatment period. No correlation was found between absolute levels of IgA, IgG or IgM RF and disease activity before or after 6 months' therapy but there was a highly significant linear correlation between reduction in IgG RF levels and fall in disease activity (r = 0.642, p less than 0.005) with treatment.

Histological techniques and paraldehyde-fuchsin (PAF) staining were used to study the synganglion and to locate neurosecretory regions and neurosecretion within the synganglion of the chicken mite, Dermanyssus gallinae. The synganglion, which is formed internally by neuropilar ganglia, gives rise to a single esophageal and paired cheliceral, palpal, pedal (I-IV), and opisthosomal nerves. The neuropilar ganglia are interconnected by commissures and connectives within the synganglion. Twelve PAF-positive neurosecretory regions are present in unfed protonymphs, unfed deutonymphs, virgin males and females, and mated males. There are 11 PAF-positive neurosecretory regions in larvae, 24-72 hours post-fed deutonymphs and mated females. Neurosecretory regions in these developmental stadia are described in relation to their positions adjacent to individual neuropilar ganglia.

A simple radioimmunoassay suitable for the routine estimation of IgG rheumatoid factors (IgG RF) has been developed. This involves determination of the amount of IgG RF binding to highly purified human IgG Fc on microtiter plates using a radiolabelled F(ab')2 preparation of an antihuman IgG Fd antiserum. A correction for nonspecific binding is made by subtracting sample reactivity with bovine serum albumin. Significantly elevated IgG RF levels were found only in patients with symmetrical peripheral erosive polyarthritis and in some patients with "mixed connective tissue disease."

The effects of different temperatures on the expression of autogenic development in unfed/mated Ornithodoros parkeri Cooley females were examined. High temperature (29 C) induced autogeny in lower, middle and higher weight classes (11-20, 21-30, 31-40 mg, respectively) with all females in the highest weight class and most in the middle weight class ovipositing within 51 days post-mate. At a lower temperature (21 C) autogenic development was not expressed by higher and middle weight females, whereas lower weight females exhibited similar degrees of autogeny at both temperatures. Results are discussed in relation to presumptive factors involved in the control and mediation of autogeny.

A simple method for isolating highly purified eosinophils from human blood is described. Buffy coats from normal individuals (eosinophil counts less than 0.4 x 10(9)/litre) were centrifuged through a two layer Percoll density gradient, to produce a granulocyte fraction containing neutrophils and eosinophils. Neutrophils were extracted from this fraction using a monoclonal antibody (CLB FcR gran 1) against CD 16 (Fc gamma R III) in a direct or indirect selection procedure using immunomagnetic beads (Dynabeads). This negative immunoselection produced eosinophils of greater purity and with a superior capacity to mount a respiratory burst than eosinophils isolated by a method employing metrizamide.

This paper describes an inexpensive, space-saving, and labor-efficient method for housing and making repeated observations of individual ticks held under specific photoperiodic, temperature, and humidity conditions. Using 96-well assay plates to house ticks, various developmental parameters, sex, survival, etc., of several thousand individual ticks can be recorded routinely in less than 1 hr. This design also permits more than 3,500 individual ticks to be maintained in 1 small (18.9-L) aquarium that serves as a humidity chamber. A small, unilluminated constant temperature incubator was converted inexpensively into a light and temperature programmable unit to contain the aquarium by adding a timing system, light fixture, and a second thermostat.

Sperm induction pores, tubuli annulati, rami sacculi, sacculus foemineus, cornu sacculus and acantho-membranous hood in female Dermanyssus gallinae support the probability of coxal insemination as reported for some other mesostigmatid species. Development of the circular testis in males (from fusion of two anterolaterally projecting protonymphal testicular arms) and formation of haploid (n = 3) spermatids from haploid (n = 3) spermatogonial cells is entirely mitotic. Spermatogenesis begins within one hour after protonymphal feeding and continues through adult ecdysis in normally fed individuals. Nutritional deficit causes cessation of spermatogenic divisions in deutonymphs starved 23 days, but is rapidly rejuvenated upon feeding. No rejuvenation of division was observed in adult males given the opportunity to feed, thus adult males might not feed., (Copyright © 1976 Wiley-Liss, Inc.)