Structure-activity relationships of organic acid anhydrides as antigens in an animal model

Relationships between chemical structure and immunogenicity have been studied in 13 dicarboxylic acid anhydrides. Guinea-pigs were immunized intradermally by a single dose of 0.3 M solutions of succinic anhydride (SA), maleic anhydride (MA), methylmaleic anhydride (MMA), cis-cyclohexane-1,2-dicarboxylic anhydride (cis-HHPA), trans-cyclohexane-1,2-dicarboxylic anhydride (trans-HHPA), 4-methylcyclohexane-1,2-dicarboxylic anhydride (MHHPA), cis-1,2,3,6-tetrahydrophthalic anhydride (THPA1236), cis-3,4,5,6-tetrahydrophthalic anhydride (THPA3456), cis-3-methylcyclohex-4-ene-1,2-dicarboxylic anhydride (MTHPA34), cis-4-methylcyclohex-4-ene-1,2-dicarboxylic anhydride (MTHPA44), phthalic anhydride (PA), 4-methylphthalic anhydride (MPA), and trimellitic anhydride (TMA) in olive oil. Specific IgE, IgG, IgG1, and IgG2 antibodies against guinea-pig serum albumin conjugates of the anhydrides were determined by passive cutaneous anaphylaxis (PCA) tests and enzyme-linked immunoabsorbant assay (ELISA). Specific IgG was significantly increased in all animals, except those immunized with THPA3456 and SA, which sensitized only 3/9 and 7/9 animals, respectively. Furthermore, the specific IgG values were very low in the SA group. The titers of specific IgG1 and IgG2 were increased in the IgG-positive animals. Specific IgE was positive in all animals immunized with MA, MHHPA, MTHPA (both isomers), and MPA, and in 6/9 and 5/9 guinea pigs immunized with TMA and MMA, respectively. The IgE titers were generally very low; PCA was negative after dilutions to 1:32, or less. The results indicate a considerable variation in the sensitizing potential between different organic acid anhydrides. The most marked general effect of the chemical structure on immunogenicity was the enhancement of antibody formation when a hydrogen atom in the anhydride was substituted with a methyl group.

Salicylate-enhanced exposure of Klebsiella pneumoniae subcapsular components

The capsular polysaccharide (CPS) of Klebsiella pneumoniae is an important virulence factor. Salicylate, which inhibits CPS production, was used to expose subcapsular antigens and components that may play an important role in host defense. Salicylate treatment greatly increased phagocytosis of five O1 serotypes by human polymorphonuclear leukocytes with normal rabbit serum and rabbit antisera against purified O1 lipopolysaccharide (O1LPS) as opsonins (p < 0.01 or < 0.05). Similar results were obtained with rabbit antiserum against a non-encapsulated isogenic strain. To further determine how salicylate increases susceptibility to phagocytosis, the binding of monoclonal antibodies against O1LPS or the LPS core and the binding of complement component C3b were measured by ELISA. The data indicate that salicylate reduced the barrier of CPS in serotypes O1:K1, O1:K10, and O1:K16 and unmasked subcapsular antigenic components in serotypes O1:K2 and O1:K66 so that bound opsonins could react with receptors on phagocytes. Serum bactericidal assays supported this conclusion. Therefore, decapsulating agents such as salicylate accentuate phagocytosis of K. pneumoniae by making subcapsular antigens and components accessible to immune and nonimmune host defences and vaccination with subcapsular antigens may exhibit optimal protection against lethal infection when combined with salicylate therapy.

Calcium-dependent conformation of a mouse macrophage calcium-type lectin. Carbohydrate binding activity is stabilized by an antibody specific for a calcium-dependent epitope

We established monoclonal antibodies (mAbs) against the mouse macrophage galactose/N-acetylgalactosamine-specific lectin (MMGL) that is a 42-kDa calcium-dependent lectin, using a solid phase carbohydrate binding assay as a novel strategy for screening mAbs. The specificity of six mAbs were investigated by antibody binding to native or recombinant forms (rML) of MMGL, flow cytometry, and immunoprecipitation using a macrophage cell line RAW264.7. Four of these mAbs strongly inhibited the binding of fluorescein 5-isothiocyanate-labeled galactosylated polylysine to immobilized rML, one inhibited moderately, and one did not inhibit binding. The competitive binding study revealed that the binding sites of these four blocking mAbs were closely related to each other but were different from the rest of these mAbs. A non-blocking mAb having a unique binding specificity (LOM-11) exhibited calcium-dependent binding to rML, suggesting that calcium-dependent epitope was not situated in the vicinity of the ligand binding site. Furthermore, pretreatment of rML with the mAb LOM-11 preserved ligand binding activity, especially in a low calcium environment. The four blocking mAbs mentioned above facilitated the binding of the mAb LOM-11 to rML. These results indicate that there is a positive cooperativity between the lectin's ligand binding site and its physically distinct calcium-dependent epitope.

Anti-lipid A monoclonal antibodies alter human endothelial cell ICAM-1 expression in vitro

Two murine anti-lipid A MAbs (A78S1 and A523), which were protective in a rat model of neonatal endotoxin shock (Goto, M, Zeller WP, Hurley RM, Jong JS, Lee C-H: Prophylaxis and treatment of newborn endotoxic shock with anti-lipid A monoclonal antibodies. Circ Shock 35:60-64, 1991), were tested for their effects on lipid A-induced ICAM-1 expression by cultured human umbilical vein endothelial cells (HUVEC). In the presence of 5% fetal bovine serum, lipid A-induced ICAM-1 expression, as measured by radioimmunoassay following 18 h incubation, was enhanced by A78S1 at lower concentrations (.02-.2 micrograms/ mL) but was inhibited at concentrations of 20 micrograms/mL or greater. Its control immunoglobulin, purified nonspecific IgG2b, enhanced the lipid A-stimulated ICAM expression at all concentrations tested. Neither MAb A523 nor its control immunoglobulin, purified nonspecific IgM, had effects on the lipid A-stimulated ICAM-1 by HUVEC. Although A78S1 and A523 had no direct effects, the control immunoglobulins marginally stimulated ICAM-1 activity at their highest concentrations (possibly due to the presence of endotoxin). Furthermore, in serum-free medium all of the immunoglobulins dose-dependently stimulated ICAM-1 expression. These results demonstrate that anti-lipid A MAbs and other immunoglobulins can exhibit variable effects on unstimulated or lipid A-stimulated ICAM-1 expression by HUVEC depending upon the presence of serum, their concentration, immunoglobulin subclass, or epitope specificity.

[The effect of translam on the immune response of irradiated mice]

Experimental facts about influence of new beta-1-3;1-6-glucan, extracted from seaweed Laminaria, on immune response of mice are summarized. The ability of translam to increase the number and functional activity of immunocompetent cells taking part in humoral immune response formation. The possibility of translam using for treatment and prophylaxis of radiation affections is discussed.

[The effect of antidote preparations on the immune reactions in acute dimethyl dichlorovinyl phosphate poisoning]

Experiments on CBA mice established that acute intoxication with dimethylchlorovinyl phosphate given in a single LD50 of 1.0 increased mice splenic colony-forming cells, decreased thymic T cells, delayed hypersensitivity, natural and antibody-dependent cellular cytotoxicities, sheep splenic red blood cells, thymus-independent Vi antigen antibody production. The antidote therapy with atropine (20 mg/kg) did not stop the main manifestations of posttoxication immunodeficiency and enhanced the suppression of a humoral immune response to sheep red blood cells. Dipyroxim (15 mg/kg) diminished manifestations of postintoxication immunodeficiency.

Allosteric regulation by calcium of rabbit polyclonal anti-cyclic GMP antibody

Calcium increased the binding of rabbit polyclonal antibodies and cGMP by increasing antibody affinity without altering the number of binding sites (Bmax). Competitive binding studies revealed that calcium increased the affinity of antibody for cGMP derivatives similarly, suggesting that the effects of this cation were antigen-independent. Kinetic binding studies demonstrated that calcium increased affinity by decreasing the dissociation rate without altering the association rate of antigen and antibody. Studies of the dissociation of antigen-antibody complexes preformed in the absence of calcium suggested that this cation regulated antibody function allosterically. These data contrast with those obtained previously suggesting that calcium regulated the interaction of cAMP and antibodies by increasing Bmax without altering affinity by reaction coupling. Re-analysis of those data demonstrated that calcium increased the affinity without altering the number of binding sites of antibodies to cAMP, in close agreement with the present results. These data suggest that allosteric modulation of antibody function by calcium may be a general mechanism regulating the interaction of polyclonal antibodies with cyclic nucleotides.

Interaction of heparin with antiphospholipid antibodies (APA) from the sera of women with recurrent pregnancy loss (RPL)

PROBLEM

To determine if heparin may act directly with antiphospholipid antibodies (APA) to prevent recurrent pregnancy loss (RPL).

METHOD

Patients were seen at the University of Texas Southwestern Medical Center. Twenty women with a history of RPL (> or = 3 miscarriages), positive APA, and an otherwise normal evaluation were treated with heparin in two daily subcutaneous dosages during a successful pregnancy. APA levels were obtained prior to conception and again at 6, 20, and 30 weeks.

RESULTS

Heparin reduced APA binding to cardiolipin and phosphatidylserine in a dose-dependent fashion in ELISA. Heparin affinity chromatography absorbed over 80% of the IgG anticardiolipin antibody in serum from women with high levels of APA. Women treated with increasing dosages of heparin during pregnancy had inversely decreasing levels of IgG anticardiolipin antibody.

CONCLUSION

Heparin may act by directly binding APA in vivo, thereby decreasing the adverse effects of APA in women with APA associated RPL.

Effect of the EGb 761 (Ginkgo bilboa extract) on primary immune response in experimental chronic stress

The effect of a chronic stress upon the primary immune response on mice was evaluated by using the plaque-forming cells (PFC)-direct technique, which allowed us to record a serious suppression of the immune response in the exposed animals. In the next phase of the experiment a second group was initially treated with Tanakan (EGb 761--Ginkgo biloba extract) and then it was submitted to the same chronic stress: this procedure did not bring about the increase of the number of lymphocytes but it significantly improved the function of these cells.

Cytosolic factors block antibody binding to the C-terminal cytoplasmic tail of the KDEL receptor

The mammalian KDEL receptor is an extremely hydrophobic membrane protein. One of the longest stretches of hydrophilic sequence resides at the C-terminus. Various antibodies against a synthetic peptide corresponding to this region confirmed that the C-terminus is exposed to the cytoplasm. It was observed that antibody binding to the C-terminus of the KDEL receptor was diminished during immunofluorescence microscopy procedures which involved fixation prior to permeabilization as compared to when cells were permeabilized before fixation. Binding of both polyclonal and monoclonal antibodies, as assessed by indirect immunofluorescence microscopy in digitonin permeabilized cells, was inhibited by preincubation with rat liver cytosol. This inhibition was not observed with antibody against another membrane protein (p28) with a cytoplasmically exposed epitope also residing in the Golgi/intermediate compartment. Rabbit reticulocyte lysate had a similar effect while Schizosaccharomyces pombe cytosol inhibited binding to a greater degree than Saccharomyces cerevisiae cytosol. This inhibition by cytosol was prevented by coincubation with the antibody and was dose-dependent on the cytosol. Inhibition did not occur on ice or at 15 degrees C, or when the cytosol was energy-depleted by apyrase treatment. Interestingly, pretreatment of permeabilized cells with N-ethylmaleimide or its addition into the incubation mixture abolished inhibition. N-ethylmaleimide-treated cytosol, however, remained inhibitory. The findings suggest the existence of cytosolic factor (s) which interacts specifically with the cytoplasmic C-terminus of the KDEL receptor, which are likely to be components of the KDEL protein retrieval machinery.

Augmentation of the immune response to influenza vaccine by acetylsalicylic acid: a clinical trial in a geriatric population

The purpose of this placebo-controlled, double-blind, randomized trial was to evaluate the efficacy of oral acetylsalicylic acid (ASA), a comparatively safe, inexpensive biological response modifier, as an adjuvant to influenza vaccination in a geriatric population. 281 healthy adults, 65 years or older, received influenza vaccine and were randomized to ASA or placebo. Serum antibody against influenza A/Beijing and B/Panama, influenza antigen-stimulated blastogenesis and antigen-stimulated interleukin-2 production by peripheral blood mononuclear cells in vitro were increased following vaccination. Blastogenic response and interleukin-2 production increased to a similar extent in the two treatment groups. The proportion of participants with a 4-fold rise in specific antibody directed against influenza A/Beijing was greater among ASA recipients (p < 0.05). This difference was more marked in subjects > 75 years old (p < 0.01).

Effects of pH or ionic strength on the reactivities of mono- and polyspecific IgG antibodies

The reactivities of mono- and polyspecific mouse monoclonal antibodies (mAb) were compared by ELISA using immobilized antigens under different conditions, varying the pH or the NaCl concentration. The monospecific group was composed of 6 IgG directed against Staphylococcus aureus capsular polysaccharides and of 3 IgG specific to actin, myosin or tubulin. These antibodies were compared with 6 polyreactive mAb also of the IgG isotype. Marked differences were noted between the reactivities of the mono- and polyreactive IgG. pH variations had little or no effect on the reactivity of monospecific mAb to polysaccharides or to proteins. In contrast, the binding of polyreactive mAb was dependent on the pH, and the profile differed for each antigen. The NaCl concentration had opposite effects on mono- and polyreactive mAb: the binding of almost all the monoreactive mAb was increased at high NaCl concentration, while it was decreased for polyreactive mAb. In contrast, the effects of varying the pH or ionic strength on the coated antigens were negligible. The variation coefficients calculated for the pH and NaCl concentration were higher for the polyreactive mAb under study, which seems to indicate that electrostatic interactions and charged residues might be more important for these mAb than for the monoreactive ones. This characteristic might be one explanation for the particular properties of these polyreactive antibodies.

Monoclonal antibodies for Streptomyces lividans and their use for immunomagnetic capture of spores from soil

Monoclonal antibodies were produced to Streptomyces lividans spore surface antigens. One particular hybridoma cell line, 43H6, produced a monoclonal antibody that reacted exclusively with Streptomyces cluster group 21 in an enzyme-linked immunosorbent assay (ELISA). Antibody 43H6 was found to be of subclass IgG1, kappa light chain. Western blot (immunoblot) analysis revealed that 43H6 recognized a major outer spore polypeptide of about 37,000 Da. The epitope was stably maintained in S. lividans spores over at least seven sporulation cycles on laboratory medium and for at least 14 weeks in sterile soil systems. The species group specificity of antibody 43H6 was exploited in the development of an immunocapture technique for the isolation of streptomycetes from soil. Magnetic beads coated with antibody 43H6 were mixed with soil samples seeded with S. lividans spores. Spore-bead complexes were recovered using magnets. Treatment of beads with blocking agents and the inclusion of detergents in the recovery system lessened non-specific binding of spores to beads and improved recovery. In buffer solutions decreasing the spore concentration increased the recovery values for a fixed bead concentration. At a spore concentration of 5 x 10(7) ml-1 the recovery was 4.3% whilst at 5 x 10(2) ml-1 it was 76% for a fixed bead concentration of 0.6 mg ml-1. Using a bead concentration of 2 mg per 10 g soil, approximately 30% of the target spore population of 10(6) c.f.u. was recovered from sterile soil and 4% from non-sterile soil. This method offers a rapid means of selectively recovering and concentrating Streptomyces spores from soil samples.

Studies on the intermolecular forces involved in the antibody-antigen interactions, using V3 synthetic peptides and sera from HIV1 seropositive patients

The nature of physical forces responsible for the antibody-antigen (Ab-Ag) reaction was analyzed in an original system, represented by synthetic peptides derived from the V3 consensus sequences of some HIV1 subtypes gp 120 and HIV1 positive human serum. For locating antigenic determines, flexibility, hydrophilicity and hydrophobicity profiles of the V3 peptides were analysed. The hydrophilicity indicates that V3 apex borders are involved in the first stage of the reaction. The flexibility and hydrophobicity suggest that the apex of the V3 loop (GPGR/Q) is involved in the stabilization of the complex by hydrophobic interactions. Further, we followed up the influence of the dielectric constant and of the pH upon the forces established between Ab and Ag. Modifications in the dielectric constant and pH reveal a significant contribution of electrostatic and van der Waals forces in securing the intermolecular complementarity. D2O produces the highest augmentation of the antibody affinity for the most hydrophilic peptides, while a very slight one was recorded for the most hydrophobic sequence. A high affinity of antibodies for the peptides MN, R and Z was registered at an acid pH, when their His residue was protonated. On the contrary, no influence was recorded in the case of the peptide A, which does not contain any His residue.

Native oligomeric human immunodeficiency virus type 1 envelope glycoprotein elicits diverse monoclonal antibody reactivities

We synthesized and purified a recombinant human immunodeficiency virus type 1 (HIV-1) envelope (Env) glycoprotein, lacking the gp120/gp41 cleavage site as well as the transmembrane domain, that is secreted principally as a stable oligomer. Mice were immunized with separated monomeric and oligomeric HIV-1 Env glycoproteins to analyze the repertoire of antibody responses to the tertiary and quaternary structure of the protein. Hybridomas were generated and assayed for reactivity by immunoprecipitation of nondenatured Env protein. A total of 138 monoclonal antibodies (MAbs) were generated and cloned, 123 of which were derived from seven animals immunized with oligomeric Env. Within this group, a significant response was obtained against the gp41 ectodomain; 49 MAbs recognized epitopes in gp41, 82% of which were conformational. The influence of conformation on gp120 antigenicity was less pronounced, with 40% of the anti-gp120 MAbs binding to conformational epitopes, many of which blocked CD4 binding. Surprisingly, less than 7% of the MAbs derived from mice immunized with oligomeric Env recognized the V3 loop. In addition, MAbs to linear epitopes in the C-terminal domain of gp120 were not obtained, suggesting that this region of the protein may be partially masked in the oligomeric molecule. A total of 15 MAbs were obtained from two mice immunized with monomeric Env. Nearly half of these recognized the V3 loop, suggesting that this region may be a less predominant epitope in the context of oligomeric Env than in monomeric protein. Thus, immunization with oligomeric Env generates a large proportion of antibodies to conformational epitopes in both gp120 and gp41, many of which may be absent from monomeric Env.

Kainic acid induced alterations in antibody recognition of connexin43 and loss of astrocytic gap junctions in rat brain

Intracerebral administration of kainic acid (KA) in rats was previously shown to abolish immunohistochemical labelling for the astrocytic gap junction protein connexin43 (Cx43) at sites depleted of neurons (Vukelic et al: Neurosci Lett 130:120-124, 1991). This response of Cx43 has now been further investigated with a number of different sequence-specific anti-Cx43 antibodies. At lesion sites in the thalamus, striatum, and hippocampus examined immunohistochemically with an antibody against amino acids (aa's) 346-363 in the Cx43 sequence, the antibody used in the earlier study, Cx43-immunoreactivity was increased 5 h after KA injections, absent by 24 h and for up to 2 weeks post-injection, and began to return to less than normal levels by 2 to 3 weeks post-injection. Analyses of KA lesion sites with antibodies against other sequences of Cx43 (amino acids 283-298, 253-270, 241-260, 113-123, and 49-61) revealed not only the presence but in some cases an increased density of Cx43 immunoreactivity after a survival time of 1 week. Immunolabelling patterns at these sites consisted of relatively large, coarse profiles rather the fine punctate labelling typically seen in sections of normal brain. In homogenates of KA-injected striatum analyzed by Western blots, Cx43 was detected at near normal or slightly increased levels at various survival times examined. The 43 kDa phosphorylated form of Cx43 and its faster migrating 41 kDa dephosphorylated form which is generated post-mortem by a brain phosphatase were both present after standard methods of tissue preparation for Western blot analysis, while only the 43 kDa form was present in normal and KA-injected striatum after inactivation of brain metabolism by focused cranial microwave irradiation. Ultrastructural investigations of lesions sites within the thalamus revealed a virtual absence of astrocytic gap junctions. These results demonstrate that Cx43 levels initially increase after intracerebral KA treatment, that its molecular organization in resident astrocytes is altered such that epitopes that are normally accessible to antibody are hidden while those that may be hidden or relatively inaccessible are exposed, and that this molecular alteration in Cx43 is associated with loss of astrocytic gap junctions.

Chemical and immunological analysis of the Aspergillus fumigatus cell wall

Hyphal-wall preparations of Aspergillus fumigatus have been analysed by sequential treatment with KOH, nitrous acid and again with KOH. By acidification of the alkali-soluble extract, a polyglucose was precipitated which showed an X-ray diffraction pattern similar to that of (1-->3)-alpha-glucan. The remainder of the alkali-soluble fraction was precipitated with ethanol; it contained all the mannose, galactose and protein of the wall and, in addition, 6.2% of the amino sugars. This wall-associated glycoprotein, following SDS-PAGE and immunoblotting, reacted with antisera raised against several mycelial extracts of A. fumigatus. Sera from patients with aspergilloma have antibodies which recognize components of this glycoprotein. The glycoprotein nature of these antigens was shown by their ability to bind Lens culinaris lectin. In addition, the antigen/antibody binding could be disrupted by exposure of antigen to periodate oxidation, hydrolysis with dilute acid or pretreatment with a large excess of an exo-beta-D-galactofuranosidase. The alkali-insoluble fraction consisted of a covalently linked glucan-chitin complex. Nitrous acid treatment, which specifically disrupts glycosidic linkages involving glucosamine, did not solubilize much material but changed the X-ray diffraction pattern from diffuse to a pattern showing the characteristic lines of crystalline (1-->3)-beta-glucan and chitin. Most of the glucan became alkali-soluble after this treatment, and the insoluble residue appeared to contain crystalline chitin.

Inhibitory effect of epinastine on bronchoconstriction induced by histamine, platelet activating factor and serotonin in guinea pigs and rats

Effects of epinastine ((+/-)-3-amino-9,13b-dihydro-1H-dibenz[c,f]imidazo[1,5-a]azepine hydrochloride, WAL 801 CL, CAS 80012-43-7) and reference drugs on bronchoconstriction induced by histamine, platelet activating factor (PAF) and serotonin were studied in guinea pigs and rats. Oral administration of epinastine resulted in a potent inhibition on bronchoconstriction induced by all three bronchoconstrictor agents, and especially, an inhibitory effect on histamine-induced response was remarkable. The effect of epinastine was stronger than that of ketotifen in inhibiting the responses induced by both PAF and serotonin. However, the extent of inhibition in the latter was less remarkable than that seen after histamine. Azelastine was 1.36-4.57 times less potent than epinastine in inhibiting the bronchoconstriction induced by either bronchospasmogen. Although promethazine displayed inhibitory effects on the responses induced by histamine, PAF and serotonin, the inhibiting potency was distinctly inferior to that of epinastine.

Structure activity relationships of peroxynitrite scavengers an approach to nitric oxide neurotoxicity

Nitric oxide (NO) is made by NO synthase during the conversion of arginine to citrulline. Researchers have found that they can block the actions of excitotoxins by inhibiting NO synthase. Released from excitable cells during trauma, NO may react with superoxide to form peroxynitrite. Once formed, peroxynitrite and its products can then react with proteins, lipids and nucleic acids resulting in cell injury and death. The present study was undertaken to investigate analogs of cysteine as scavengers of peroxynitrite. Peroxynitrite scavengers were assayed by Attoflo, an automated radioimmunoassay. Briefly, peroxynitrite, in a dose-dependent manner (0.1 to 10 mM), inhibited the binding of I125 cAMP to a polyclonal antibody used in the assay of cAMP. Drugs were tested for blockade of the inhibition (90%) caused by peroxynitrite at 10 mM. Cysteine blocked the inhibition of ligand/antibody binding in a dose-dependent manner (EC50 = 3 mM). Cysteine, cysteine esters, penicillamine, penicillamine esters and cysteamine were the most effective peroxynitrite scavengers. Analogs of cysteine may thereby protect cells from nitric oxide toxicity.

Heparin specifically inhibits binding of V3 loop antibodies to HIV-1 gp120, an effect potentiated by CD4 binding

OBJECTIVE

To investigate the binding of the sulphated polysaccharides, dextran sulphate and heparin, to CD4 and gp120 in order to examine the anti-HIV mechanisms of these compounds.

DESIGN

In order to study the molecular mechanisms involved, the binding of sulphated polysaccharides to recombinant (r) sCD4 and gp120 was investigated in solid-phase binding studies that employed various monoclonal antibodies directed against known epitopes on these proteins, including the V3 loop of gp120.

METHODS

The ability of sulphated polysaccharides to inhibit both the binding of gp120 to CD4 and the binding of the monoclonal antibodies was investigated by enzyme-linked immunosorbent assays.

RESULTS

It was demonstrated that dextran sulphate inhibits gp120-sCD4 binding at concentrations of 100 micrograms/ml, whereas heparin has no effect. Heparin does, however, block the binding to rgp120 of monoclonal antibodies recognizing epitopes in the V3 loop. Clinical low molecular weight heparin preparations are as active as unfractionated heparin in this regard. Pre-incubation of gp120 with excess sCD4 increases the potency of heparin in blocking the binding of V3 loop monoclonals severalfold.

CONCLUSIONS

The modes of action of heparin and dextran sulphate differ. Dextran sulphate both inhibits CD4-gp120 binding and binds to the V3 loop of gp120. However, heparin is more selective and appears to function only by interfering with events involving the V3 loop that occur prior to HIV fusion with the plasma membrane.

Immunotoxicity of mono-nitrotoluenes in female B6C3F1 mice: I. Para-nitrotoluene

para-Nitrotoluene (p-nitrotoluene) is used primarily as an intermediate in the production of various dyes, explosives, pharmaceuticals, and in the production of rubber and agricultural products. Previous investigations indicated that p-nitrotoluene was mutagenic in the Ames Test and that other mono-substituted nitrotoluenes bound covalently to hepatic macromolecules. The objective of these studies was to evaluate the potential immunotoxicity of p-nitrotoluene in mice exposed by the oral route. Mice exposed to p-nitrotoluene (200-600 mg/kg) daily for 14 days showed modest dose-dependent increases in liver and spleen weights. The livers of mice exposed subchronically to 400 and 600 mg/kg showed a mild to moderate swelling of the hepatocytes adjacent to the central veins; this swelling appeared to be reversible and there was no evidence of necrosis. The proportion of monocytes in blood was decreased in mice treated with p-nitrotoluene or toluene. Serum chemistries, bone marrow cellularity and the number of CFU-M and CFU-GM were unaffected. Immunologic investigations showed p-nitrotoluene suppressed the IgM response to sRBC and the DHR response to KLH. There was a 24% decrease in the percentage of CD4+ T lymphocytes in the spleen. There was no dose-dependent alteration of peritoneal macrophage numbers or differential count, unstimulated natural killer cell activity, response to B cell mitogen LPS, C3 activity or interferon levels. Exposure of mice to p-nitrotoluene decreased resistance to Listeria monocytogenes but not to Streptococcus pneumoniae, Plasmodium yoelii or the B16F10 melanoma, and increased resistance to the PYB6 tumor. These studies indicated that the immune system is an important target for toxicity of p-nitrotoluene. The decreased host resistance to L. monocytogenes can be attributed to the decrease in T lymphocytes and to a decreased delayed hypersensitivity response to KLH.

The effects of PEG on second antibody immunoprecipitation and its use in immunoassay

The effects of PEG on the second antibody immunoprecipitation have been studied in several radioimmunological systems. The following parameters have been studied in the assays: the average molecular weight and concentration of PEG, the species of the animal producing the first and second antibody, the nature of the antigen, the concentration of carrier immunoglobulins, and the rate of the immunoprecipitation. Thus, optimal conditions for the use of PEG with a second antibody have been defined in order to be used in any liquid phase immunoassay.

Specific disengagement of cell-bound anti-LAM-1 (anti-L-selectin) antibodies by aurintricarboxylic acid

Brief treatment of human peripheral blood lymphocytes with the potential anti-HIV compound aurintricarboxylic acid (ATA) prompts the selective release of already bound L-selectin-specific anti-Leu8 and anti-LAM1-1 antibodies from the cells. Two other anti-LAM1 antibodies, anti-LAM1-3 and anti-LAM1-5 stay antigen-bound at the same time. Interestingly, the ATA-sensitive anti-Leu8 strongly competes with the ATA-resistant anti-LAM1-3 for binding. Photobleaching fluorescence resonance energy transfer (pFRET) measurements on flow-sorted cells suggests that these two antibodies compete for the same epitope, while anti-LAM1-5-FITC and anti-Leu8-PE bind to distinct sites, although they also compete for binding. Combining the data on competition, pFRET and ATA effect, we suggest that the ATA sensitive anti-Leu8 and resistant anti-LAM1-3 bind to overlapping but non-identical epitopes. This remarkably specific effect may be exploited for designing anti-inflammatory drugs that modulate leukocyte adhesion.

[The effect of chorionic gonadotropin on the formation of a secondary immune response]

Investigations have been carried out in experimental systems in vivo on noncastrated and ovariectomized female [correction of male] mice and in vitro. The secondary immune response to sheep erythrocytes has been estimated on the 5-th day after reimmunization by IgM and IgG levels in the antibody-forming cells (AFC). It has been established, that in a dose of 40, IU, chorionic gonadotropin (CG) does not influence the formation of a secondary immune response. All the effects of the hormone are associated with the dose of 200 IU, extrapolated from the maximum CG level during pregnancy. CG in this dose reduces spleen cellularity and suppresses the PFC formation processes. Ovarian sexual steroids do not mediate CG immunodepressive effects, but they are able to abolish the effect of G-AFC depression. An hour preincubation of CG (200 IU) with sensitized splenocytes in vitro suppresses M-AFC formation processes. So, if CG (200 IU) interacts with immunocompetent cells before their repeated contact with antigen, the M-AFC counts decreases; after reimmunization the G-AFC counts decreases.