Ultrasmall and Highly Dispersed Pt Entities Deposited on Mesoporous N-doped Carbon Nanospheres by Pulsed CVD for Improved HER.

Vapor-based deposition techniques are emerging approaches for the design of carbon-supported metal powder electrocatalysts with tailored catalyst entities, sizes, and dispersions. Herein, a pulsed CVD (Pt-pCVD) approach is employed to deposit different Pt entities on mesoporous N-doped carbon (MPNC) nanospheres to design high-performance hydrogen evolution reaction (HER) electrocatalysts. The influence of consecutive precursor pulse number (50-250) and deposition temperature (225-300 °C) are investigated. The Pt-pCVD process results in highly dispersed ultrasmall Pt clusters (≈1 nm in size) and Pt single atoms, while under certain conditions few larger Pt nanoparticles are formed. The best MPNC-Pt-pCVD electrocatalyst prepared in this work (250 pulses, 250 °C) reveals a Pt HER mass activity of 22.2 ± 1.2 A mg-1 Pt at -50 mV versus the reversible hydrogen electrode (RHE), thereby outperforming a commercially available Pt/C electrocatalyst by 40% as a result of the increased Pt utilization. Remarkably, after optimization of the Pt electrode loading, an ultrahigh Pt mass activity of 56 ± 2 A mg-1 Pt at -50 mV versus RHE is found, which is among the highest Pt mass activities of Pt single atom and cluster-based electrocatalysts reported so far.

Ultrahigh Mass Activity Pt Entities Consisting of Pt Single atoms, Clusters, and Nanoparticles for Improved Hydrogen Evolution Reaction.

Platinum is one of the best-performing catalysts for the hydrogen evolution reaction (HER). However, high cost and scarcity severely hinder the large-scale application of Pt electrocatalysts. Constructing highly dispersed ultrasmall Platinum entities is thereby a very effective strategy to increase Pt utilization and mass activities, and reduce costs. Herein, highly dispersed Pt entities composed of a mixture of Pt single atoms, clusters, and nanoparticles are synthesized on mesoporous N-doped carbon nanospheres. The presence of Pt single atoms, clusters, and nanoparticles is demonstrated by combining among others aberration-corrected annular dark-field scanning transmission electron microscopy, X-ray absorption spectroscopy, and electrochemical CO stripping. The best catalyst exhibits excellent geometric and Pt HER mass activity, respectively ≈4 and 26 times higher than that of a commercial Pt/C reference and a Pt catalyst supported on nonporous N-doped carbon nanofibers with similar Pt loadings. Noteworthily, after optimization of the geometrical Pt electrode loading, the best catalyst exhibits ultrahigh Pt and catalyst mass activities (56 ± 3 A mg-1 Pt and 11.7 ± 0.6 A mg-1 Cat at -50 mV vs. reversible hydrogen electrode), which are respectively ≈1.5 and 58 times higher than the highest Pt and catalyst mass activities for Pt single-atom and cluster-based catalysts reported so far.

Mechanistic Understanding of Water Oxidation in the Presence of a Copper Complex by In Situ Electrochemical Liquid Transmission Electron Microscopy.

The design of molecular oxygen-evolution reaction (OER) catalysts requires fundamental mechanistic studies on their widely unknown mechanisms of action. To this end, copper complexes keep attracting interest as good catalysts for the OER, and metal complexes with TMC (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) stand out as active OER catalysts. A mononuclear copper complex, [Cu(TMC)(H2O)](NO3)2 (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), combined both key features and was previously reported to be one of the most active copper-complex-based catalysts for electrocatalytic OER in neutral aqueous solutions. However, the functionalities and mechanisms of the catalyst are still not fully understood and need to be clarified with advanced analytical studies to enable further informed molecular catalyst design on a larger scale. Herein, the role of nanosized Cu oxide particles, ions, or clusters in the electrochemical OER with a mononuclear copper(II) complex with TMC was investigated by operando methods, including in situ vis-spectroelectrochemistry, in situ electrochemical liquid transmission electron microscopy (EC-LTEM), and extended X-ray absorption fine structure (EXAFS) analysis. These combined experiments showed that Cu oxide-based nanoparticles, rather than a molecular structure, are formed at a significantly lower potential than required for OER and are candidates for being the true OER catalysts. Our results indicate that for the OER in the presence of a homogeneous metal complex-based (pre)catalyst, careful analyses and new in situ protocols for ruling out the participation of metal oxides or clusters are critical for catalyst development. This approach could be a roadmap for progress in the field of sustainable catalysis via informed molecular catalyst design. Our combined approach of in situ TEM monitoring and a wide range of complementary spectroscopic techniques will open up new perspectives to track the transformation pathways and true active species for a wide range of molecular catalysts.

Molecular and heterogeneous water oxidation catalysts: recent progress and joint perspectives.

The development of reliable water oxidation catalysts (WOCs) is essential for implementing artificial photosynthesis on a large technological scale. WOC research has evolved into two major branches, namely molecular and heterogeneous catalysts. Manifold design principles and plenty of mechanistic insights have been developed in these individual fields after decades of investigations. Over the past years, a growing need for knowledge transfer between both sides has emerged in order to expedite the development and optimization of next-generation WOCs. In this review, we first provide selected recent highlights in the area of molecular WOCs with different nuclearities, together with current mechanistic insight. WOCs offering molecular integrity under operational conditions are ideal platforms for elucidating reaction mechanisms and well-defined structure-function correlations at the atomic level. Next, recent mechanistic advances and design strategies for heterogeneous WOCs are illustrated for representative examples, together with a discussion of their inherent limitations in mechanistic studies. Finally, illustrative cases of knowledge transfer between molecular and heterogeneous WOCs are discussed to highlight the advantages of combining the best of both catalyst types. For the sake of conciseness, this review focuses primarily on WOCs based on the first-row transition metals, which are attracting increasing attention for both fundamental studies and economic applications.

Stabilization of different redox levels of a tridentate benzoxazole amidophenoxide ligand when bound to Co(iii) or V(v).

A tridentate benzoxazole-containing aminophenol ligand NNOH2 was coordinated to Co and V metal centers and the electronic structure of the resultant complexes characterized by both experimental and theoretical methods. The solid state structure of the Co complex exhibits a distorted octahedral geometry with two tridentate ligands bound in meridional fashion, and coordination-sphere bond lengths consistent with a Co(iii) oxidation state. EPR and magnetic data support a S = 1/2 ground state, and a formal electronic description of Co(iii)(NNOAP)(NNOISQ) where NNOAP corresponds to an amidophenoxide and NNOISQ to the iminosemiquinone redox level. However, the metrical parameters are similar for both ligands in the solid state, and DFT calculations support delocalization of the ligand radical over both ligands, affording an intermediate ligand redox level Co(iii)(NNO1.5-)(NNO1.5-). The vanadyl complex exhibits a distorted octahedral geometry in the solid state consistent with a V(v) metal center and amidophenoxide (NNOAP), acetylacetonate and oxo ligands. The ligand metrical parameters are consistent with significant amidophenoxide to V(v) π donation. Overall, our results highlight the roles of electron transfer, delocalization, and π bonding in the metal complexes under study, and thus the complexity in assignment of the electronic structure in these systems.

A neutron scattering soil moisture measurement system with a linear response.

A prototype moisture measurement system was designed and constructed, based on neutron scattering, for preforming measurements in the laboratory. The system consisted of a rectangular soil container, an 241Am/Be neutron source and two parallel 10BF3 detectors (one near the source and the other far from it). Neutrons from the source are moderated and backscattered within the soil sample before being detected by two parallel counters, whose count ratios are shown to be linearly related to the soil moisture even within short measurement times. The system's performance was demonstrated using the Monte Carlo simulations, and a series of measurements on soil samples made of clay (40 wt%) and sand (60 wt%), mixed with different percentages of water. The results showed that the detectors response ratio is linear, up to about 25% of water content.

Bi2O2CO3 Growth at Room Temperature: In Situ X-ray Diffraction Monitoring and Thermal Behavior.

The room-temperature formation of bismuth oxycarbonate (Bi2O2CO3) from Bi2O3 in sodium carbonate buffer was investigated with in situ powder X-ray diffraction (PXRD) in combination with electron microscopy and vibrational spectroscopy. Time-resolved PXRD measurements indicate a pronounced and rather complex pH dependence of the reaction mechanism. Bi2O2CO3 formation proceeds within a narrow window between pH 8 and 10 via different mechanisms. Although a zero-dimensional nucleation model prevails around pH 8, higher pH values induce a change toward a diffusion-controlled model, followed by a transition to regular nucleation kinetics. Ex situ synthetic and spectroscopic studies confirm these trends and demonstrate that in situ monitoring affords vital parameter information for the controlled fabrication of Bi2O2CO3 materials. Furthermore, the ß â†’ α bismuth oxide transformation temperatures of Bi2O2CO3 precursors obtained from different synthetic routes differ notably (by min 50 °C) from commercially available bismuth oxide. Parameter studies suggest a stabilizing role of surface carbonate ions in the as-synthesized bismuth oxide sources. Our results reveal the crucial role of multiple preparative history parameters, especially of pH value and source materials, for the controlled access to bismuth oxide-based catalysts and related functional compounds.

Proposed mechanisms for water oxidation by Photosystem II and nanosized manganese oxides.

Plants, algae and cyanobacteria capture sunlight, extracting electrons from H2O to reduce CO2 into sugars while releasing O2 in the oxygenic photosynthetic process. Because of the important role of water oxidation in artificial photosynthesis and many solar fuel systems, understanding the structure and function of this unique biological catalyst forms a requisite research field. Herein the structure of the water-oxidizing complex and its ligand environment are described with reference to the 1.9Å resolution X-ray-derived crystallographic model of the water-oxidizing complex from the cyanobacterium Thermosynechococcus vulcanus. Proposed mechanisms for water oxidation by Photosystem II and nanosized manganese oxides are also reviewed and discussed in the paper.

Photobiological hydrogen production and artificial photosynthesis for clean energy: from bio to nanotechnologies.

Global energy demand is increasing rapidly and due to intensive consumption of different forms of fuels, there are increasing concerns over the reduction in readily available conventional energy resources. Because of the deleterious atmospheric effects of fossil fuels and the uncertainties of future energy supplies, there is a surge of interest to find environmentally friendly alternative energy sources. Hydrogen (H2) has attracted worldwide attention as a secondary energy carrier, since it is the lightest carbon-neutral fuel rich in energy per unit mass and easy to store. Several methods and technologies have been developed for H2 production, but none of them are able to replace the traditional combustion fuel used in automobiles so far. Extensively modified and renovated methods and technologies are required to introduce H2 as an alternative efficient, clean, and cost-effective future fuel. Among several emerging renewable energy technologies, photobiological H2 production by oxygenic photosynthetic microbes such as green algae and cyanobacteria or by artificial photosynthesis has attracted significant interest. In this short review, we summarize the recent progress and challenges in H2-based energy production by means of biological and artificial photosynthesis routes.

Synthesis, characterization and catalytic activity of copper(II) complexes containing a redox-active benzoxazole iminosemiquinone ligand.

A tridentate benzoxazole-containing aminophenol ligand HL(BAP) was synthesized and complexed with Cu(II). The resulting Cu(II) complexes were characterized by X-ray, IR, UV-vis-NIR spectroscopies, and magnetic susceptibility studies, demonstrating that the ligand is oxidized to the o-iminosemiquinone form [L(BIS)](-) in the isolated complexes. L(BIS)Cu(II)Cl exhibits a distorted tetrahedral geometry, while L(BIS)Cu(II)OAc is square pyramidal. In both solid state structures the ligand is coordinated to Cu(II)via the benzoxazole, as well as the nitrogen and oxygen atoms from the o-iminosemiquinone moiety. The chloride, or acetate group occupies the fourth and/or fifth positions in L(BIS)Cu(II)Cl and L(BIS)Cu(II)OAc, respectively. Magnetic susceptibility measurements indicate that both complexes are diamagnetic due to antiferromagnetic coupling between the d(9) Cu(II) centre and iminosemiquinone ligand radical. Electrochemical studies of the complexes demonstrate both a quasi-reversible reduction and oxidation process for the Cu complexes. While L(BIS)Cu(II)X (X = Cl) is EPR-silent, chemical oxidation affords a species with an EPR signal consistent with ligand oxidation to form a d(9) Cu(II) iminoquinone species. In addition, chemical reduction results in a Cu(II) centre most likely bound to an amidophenoxide. Mild and efficient oxidation of alcohol substrates to the corresponding aldehydes was achieved with molecular oxygen as the oxidant and L(BIS)Cu(II)X-Cs2CO3 as the catalyst.

Binding specificities of a polyreactive and a monoreactive human monoclonal IgG rheumatoid factor: role of oligosaccharides.

The immunological specificites of two human rheumatoid factor-reactive IgG monoclonal antibodies derived from unstimulated rheumatoid synovial lymphocytes have been analysed. A malaria antigen-reactive IgG monoclonal antibody from an immune donor served as a control. Purified IgG monoclonal antibody from one IgG-RF hybridoma (L1), but not from the other IgG-RF hybridoma (D1) or the anti-malaria monoclonal antibody, exhibited dose-dependent binding to multiple self and non-self antigens such as ds-DNA, cytochrome-c, bovine thyroglobulin, transferrin, cellulose and lipopolysaccharide and therefore was considered polyreactive. The immunological specificity was confirmed by inhibition experiments using the same soluble antigens as inhibitors. The polyreactivity of the IgG-RF MoAb was markedly inhibited by absorption with glycoproteins such as thyroglobulin, a commonly used target for xenoreactive natural antibodies, and cytochrome-c, indicating that the monoclonal antibody is reactive with epitopes expressed on these ligands. Since some naturally occurring antibodies are carbohydrate specific, the authors tested the IgG-RF MoAb for possible carbohydrate specificity. Absorption with certain polysaccharides containing only one or two different sugar moieties did not inhibit the binding reactivities to any of the tested antigens. Polyreactivity of the monoclonal antibody, unlike most xenoreactive natural antibodies, was not caused by reactivity with (gal alpha 1-3gal) as indicated by the remaining binding reactivity after alpha-galactosidase treatment of the antigen. Removal of the N-linked glycosylation sites within the Fc portion of target IgG markedly reduced the antibody binding. The findings suggest that the carbohydrate content of the antigen is necessary for binding of the polyreactive IgG-RF MoAb. Reactivity to carbohydrate antigens may readily explain the so-called multispecificity of certain antibodies.

Mercury induces polyclonal B cell activation, autoantibody production and renal immune complex deposits in young (NZB x NZW)F1 hybrids.

It is well established that in susceptible mouse strains, chronic treatment with subtoxic doses of mercuric chloride (HgCl2) induces a systemic autoimmune disease, which is characterized by increased serum levels of IgG1 and IgE antibodies, by the production of anti-nucleolar antibodies and by the development of immune complex-mediated glomerulonephritis. Susceptibility to mercury is partly under the control of major histocompatibility complex genes. To study the susceptibility to mercury further, we investigated the in vivo effects of mercury in young autoimmune disease prone (NZB x NZW)F1 (H-2d/z) mice prior to establishment of spontaneous autoimmune disease. Mercury-susceptible SJL (H-2s) mice and mercury low-responder BALB/c (H-2d) mice were used as positive and negative controls, respectively. In (NZB x NZW)F1 mice, treatment with mercury stimulated an intense antibody formation characterized by increased numbers of splenic IgG1 and IgG3 antibody-producing cells as well as by elevated serum IgE levels. Injection with mercury also induced an increased production of IgG1, IgG2b and IgE antibodies in SJL, but not in BALB/c mice. The mercury-induced IgG1 response in (NZB x NZW)F1 and SJL mice was found to be polyclonal and autoantibodies against double-stranded (ds)DNA, IgG, collagen, cardiolipin, phosphatidylethanolamine as well as antibodies against the hapten trinitrophenol were produced. In addition, SJL, but not (NZB x NZW)F1 or BALB/c mice, produced IgG1 anti-nucleolar antibodies after treatment with mercury. Further studies demonstrated that (NZB x NZW)F1 and SJL mice developed high titers of renal mesangial immune complex deposits containing IgG1 antibodies 3 weeks after injection with mercury. Thus, a mouse strain genetically prone to develop spontaneous autoimmune diseases is highly susceptible to mercury-induced immunopathological alterations.

Human IgG rheumatoid factors and RF-like immune complexes induce IgG1 rheumatoid factor production in mice.

The synovial fluid of patients with rheumatoid arthritis (RA) was found to contain IgG and/or IgG-containing immune complexes (ICs) that stimulated an intense antibody formation when injected into mice of certain strains, notably of NZ background. The response was characterized by high and sustained levels of IgG1 antibodies with rheumatoid factor (RF) activity. In the study described, we investigated whether it is the antibodies with RF activity in the synovial fluid, that are responsible for stimulation of mouse RF in vivo. Different mouse strains were injected with synovial fluid from a seropositive RA patient (RA-SF), with human monoclonal antibodies with RF activity, with a human non-RF monoclonal antibody or with different preformed RF-like antibody-antibody (Ab-Ab) ICs. The experimental mice were monitored subsequently for IgG1 RF production. IgG1 RF antibodies were found in all strains (NZB, BALB/c and CBA) injected with Ab-Ab ICs formed at equivalence, but only in NZB using RA-SF or human monoclonal antibodies with RF activity. Optimal production of IgG1 RF by Ab-Ab ICs required the integrity of Fc and F(ab)'2 portions respectively of the antibodies; soluble and truncated ICs were less effective. Further studies demonstrated that the IgG1 RF response was not simply the result of a specific immune response against human IgG, since humoral immunity against human IgG was induced only when combined with an efficient adjuvant. During a typical adjuvant-associated primary response specific antibodies of IgM, IgG1 and IgG2a isotypes were found, i.e. quite different from the selective IgG1 response induced by RF-like containing immune complexes. This conclusion is substantiated further by the clear differences in responses to IgG containing fraction obtained from RA-SF in NZ mice compared to other strains. Our findings argue for a different type of reaction leading to the selective IgG1 response and might aid in elucidating the mechanisms for chronic production of antibodies with RF activity in patients with RA.

Effect of surgical removal of hydatid cyst on echinococcus-specific and polyclonal IgE antibodies: An aid for postoperative follow-up studies.

To evaluate the significance of IgE antibodies in postoperative follow-up studies of patients with primary hydatidosis, 24 patients with detectable levels of Enchinococcus granulosus-specific IgE as determined by radioallergosorbent test (RAST) were re-examined one month and four months after surgical resection of the cyst. Serum levels of polyclonl IgE as determined by paper radiommunosorbent test (PRIST) were also determined before and after surgery. Anti-Enchinococcus IgE was undetected in 75% and 89% of patients with hepatic or pulmonary hydatidosis, respectively, four months after surgery. In addition, significant decline was observed in the serum polyclonal IgE four months after surgical removal of the cyst in both hepatic and pulmonary hydatidosis. However, surgical removal of pulmoary cyst alone showed no such effect on either polyclonal or Enchinococcus-specific IgE in hepatopulmonary hydatidosis. The results suggest that determination of specific an polyclonal IgE antibodies provide useful serological tests for prognosis and early detection of persistence and recurrence of hydatid disease postoperatively.

Effect of drug therapy on circulating and synovial fluid Ig-secreting cells in rheumatoid arthritis.

A common immunological abnormality in rheumatoid arthritis (RA) is an increased spontaneous polyclonal B cell activation. In order to study the influence of drug therapy in RA on the functional activity of B cells we enumerated spontaneous plaque-forming cells (PFC) in peripheral blood lymphocytes (PBL) and synovial fluid lymphocytes (SFL) by a reverse haemolytic plaque assay. Spontaneous IgG-, IgM-, and IgA-PFC in PBL of 26 patients with classical erosive RA receiving either gold salts or D-penicillamine were similar to those observed in 20 healthy controls. In contrast, significantly higher numbers of IgG- and IgA-PFC, but not IgM-PFC, were found in PBL of nine patients with classical erosive RA receiving non-steroidal anti-inflammatory drugs (NSAID) alone. Furthermore, spontaneous PFC in SFL from 16 consecutive patients with RA receiving second-line drugs, as well as 17 patients with other forms of arthritis (non-RA) were generally low and significantly less than those observed in 20 RA patients on NSAID alone. Moreover, a wide individual variation in PFC, especially in relation to the IgG class, was recorded in the synovial lymphocytes. These studies imply that treatment with second-line drugs is associated with normalisation of B cell activity in RA patients, and that the effect can be detected at the cellular level both in blood and synovial fluid.

Demonstration of a helper factor(s) with T-cell-replacing activity in synovial fluid.

Cell-free synovial fluid (SF) obtained from patients with rheumatoid arthritis contains a helper factor(s) capable of augmenting the generation of plaque-forming cells (PFC) in pokeweed mitogen (PWM)-stimulated normal peripheral blood mononuclear cells (PBMC). This helper factor behaves like a polyclonal B-cell activator, in that it triggers the formation of IgM, IgG, and IgA PFC. However, SF has little or no effect on the proliferation of PWM-activated PBMC. Furthermore, SF was capable of replacing T cells for PWM-induced differentiation but not proliferation of enriched human blood B lymphocytes. No helper factor or T-cell-replacing activity was found in SF from patients with traumatic synovitis. Fractionation of SF containing helper activity on staphylococcal protein A column indicated that the activity is induced by biologically active molecules distinct from materials that preferentially bind to protein A such as IgG immune complexes. We conclude that the present activity has striking similarities to the recently described B-cell differentiation factor that is produced by specifically activated T-cell lines in vitro.

No demonstrable association between HLA DR4 and in vitro collagen reactivity as determined by the production of leukocyte inhibition factor.

Eight HLA DR4 positive and 9 HLA DR4 negative healthy volunteers as well as 2 DR4 positive and 1 DR4 negative patients with rheumatoid arthritis (RA) were compared for leukocyte inhibition factor (LIF) production and lymphocyte proliferation in response to native and denatured collagen types II and I/III. Purified protein derivative (PPD) of tuberculin served as a positive control in the LIF assay and PPD and phytohaemagglutinin (PHA) in the lymphocyte proliferation test. No significant difference in responsiveness to collagen was detected between these two HLA groups. The reactivity to collagen was not affected by removal of OKT8+ lymphocytes. The present results are in conflict with earlier reports by Solinger et al. (1981) and Solinger & Stobo (1982). The reason for the discrepancy has not been resolved.

B cell differentiation factor in synovial fluid of patients with rheumatoid arthritis.

In this paper we have summarized our findings on immune activity in patients with Rheumatoid Arthritis. RA is characterized not only by the formation of various autoantibodies but also of a hyperreactivity of the B cell system, shown as an increased DNA synthetic rate of blood non-T, non-monocytic lymphocytes as well as an increased number of actively antibody secreting cells both in the blood and the synovial fluid. Synovial fluid contains biological activity which synergizes with PWM for the induction of Ig-secreting cells in blood from healthy controls. The factor can also substitute for T cells in the PWM-induced antibody synthesis in vitro. This activity fits well with the finding that SF contains a factor which induces increased formation of IgG in LPS-pretreated mouse cell cultures. Experiments show that the factor leads to a preferential increase in the production of IgG2b antibody secreting cells. Therefore, we conclude that synovial fluid contains a B cell differentiating factor with a selective effect on the induction of a particular IgG subclass.

Spontaneous DNA synthesis in rheumatoid arthritis: evidence of enhanced circulating non-T-cell proliferation.

3H-thymidine incorporation in cultures of peripheral blood mononuclear cells from patients with seropositive rheumatoid arthritis (RA) and healthy controls was measured in vitro in the absence of added stimulants. A significantly higher level of spontaneous DNA synthesis was found in cultures of mononuclear cells from patients with clinically active RA than from patients with inactive disease and normal controls. This activity was more apparent in 24-h cultures than in 72-h cultures. There was no correlation between DNA levels and IgM rheumatoid factor (RF) titres. When T- and non-T-cell populations were separated and cultured simultaneously with unfractionated cells, only non-T cells maintained high levels of DNA synthesis, and enrichment of surface membrane Ig+ (SmIg) cells was generally associated with enhancement of 3H-thymidine incorporation. Furthermore, no difference was found in spontaneous DNA synthesis between cultures either containing or depleted of phagocytic cells. Moreover, the addition of graded numbers of autologous monocytes to highly purified T- and non-T-cell populations did not alter the background DNA synthesis. Thus, endogenously activated cells in RA patients are neither T lymphocytes nor monocytes. A regulatory influence by monocytes could not be demonstrated. It is suggested that cells actively engaged in DNA synthesis in RA blood are non-T cells in origin, most probably B lymphocytes.

High incidence of spontaneous Ig-producing lymphocytes in peripheral blood and synovial fluid of patients with active seropositive rheumatoid arthritis.

Numbers of in vitro spontaneous IgG, IgM and IgA plaque-forming cells (PFC) as assessed by a modification of the protein A haemolytic plaque assay were determined in the blood and synovial fluid of patients with seropositive rheumatoid arthritis (RA) and compared with those of control groups. The total numbers of PFC were significantly higher in the peripheral blood of patients with active seropositive RA than in that of normal controls. In addition, most B lymphocytes in the synovial fluid of patients with active seropositive RA were active immunoglobulin (Ig) producers, whereas synovial fluid lymphocytes from patients with inactive seropositive RA and seronegative arthritis were not. In general, IgA PFC were relatively high in blood, whereas IgG PFC dominated in the synovial fluid. IgM PFC appear to be relatively low in blood and synovial fluid. However, a relative increase of IgG PFC was noted in the peripheral blood of patients with active RA. To test for polyclonality of the increased Ig synthesis, we tested the sera of patients and controls for the presence of polyclonal antibodies against sheep erythrocytes (SRBC) and SRBC modified by fluorescein isothiocyanate (FITC) and trinitrophenyl (TNP). No differences were observed with SRBC and TNP-SRBC agglutinin titres between patients and controls, but patients with RA had higher titres of FITC-SRBC agglutinins than normal sera. This finding supports the concept of a polyclonal nature of antibody production in RA patients.