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Pityrosporum ovale has recently been recognized as a source of allergens to which many patients with atopic dermatitis (AD) show type I skin reactions and specific IgE antibodies. In this study the IgE-binding components and/or epitopes in P. ovale extract were shown to be partially sensitive to pronase or trypsin treatment, whereas periodate oxidation resulted in a complete loss of IgE-binding capacity, thus suggesting the involvement of carbohydrate structures. In Con A affinity chromatography most of the IgE-binding capacity of crude P. ovale extract bound to the column, and could be eluted with mannoside. Gel filtration on Sephacryl S-400 revealed a marked heterogeneity with respect to molecular mass, with most of the IgE-binding activity associated with high-mol.-mass fractions (from 5 x 10(4) up to 2 x 10(6) Da). A similar heterogeneity was found after chromatofocusing, with IgE-binding in the whole pI-range from 7.0 to 4.0. Essentially identical results were obtained with extracts of Candida albicans, in agreement with the previously shown cross-reactivity of IgE-binding components in the two yeast extracts. In inhibition ELISA, gel filtration and chromatofocusing fractions containing components with widely different mol. mass or pI showed complete reciprocal cross-inhibition, and were all capable of inhibiting the binding of IgE to unfractionated extracts. We therefore conclude that the cross-reacting anti-P. ovale/anti-C. albicans IgE antibodies in the sera of AD patients are mainly directed at a restricted number of carbohydrate epitopes that are expressed on a heterodisperse range of high-mol.-mass components, probably mannans or mannoproteins.

Various studies have demonstrated anti-retinal S-antigen (S-ag) antibodies in uveitis sera in assays using bovine S-ag. Because of its molecular similarity and cross-reactivity with human S-ag, reactions with bovine S-ag have been considered a reliable indication of anti-S-ag autoimmunity. To test this assumption, the cross-reactivity of purified human and bovine S-ags was quantitated by ELISA titration of various anti-human and anti-bovine S-ag immune reagents raised in mice, rats and rabbits. Anti-human S-ag reagents appeared to be largely cross-reactive with bovine S-ag, whereas anti-bovine S-ag reagents were 6-10 times less reactive with the cross-reacting human S-ag than with bovine S-ag, thus showing a predominant role of species-specific epitopes on bovine S-ag. Furthermore, a large number of human control and uveitis sera was tested in ELISA with both human S-ag- and bovine S-ag-coated microwells. Both the numbers of positive sera and the levels of anti-S-ag antibodies in the two tests significantly correlated, but many exceptions were found, and the predictive value of reactions with bovine S-ag for the presence and levels of anti-S-ag autoantibodies was low. For individual human sera, assessment of anti-S-ag autoantibodies requires the use of human S-ag in immunoassays.

An enzyme-linked immunosorbent assay (ELISA) was developed to assess serum IgE antibodies directed against Pityrosporum ovale in patients with atopic dermatitis (AD), atopic patients with allergic respiratory disease (ARD: rhinitis or asthma) but without eczema, and in healthy controls. IgE binding to P. ovale extract was demonstrated in 49% (35/72) of AD patients. In contrast, anti-P. ovale IgE was found in only one of 27 atopic controls without eczema; all healthy control sera (n = 17) were negative. Of 37 AD patients tested intracutaneously with P. ovale, 31 showed immediate-type reactivity, and 20 of these 31 patients had anti-P. ovale IgE detectable by ELISA, while sera from the six non-responders were all negative. Levels of anti-P. ovale IgE were highest in AD patients aged 20-30 years. No correlation was found with the severity of AD, but there was a non-significant tendency (P = 0.06) to higher levels in AD patients with concomittant respiratory allergy. Anti-P. ovale IgE was significantly correlated with total serum IgE, with specific IgE against various aeroallergens as measured by RAST, and with levels of anti-Candida albicans IgE, measured with a similar ELISA. Thus, production of IgE antibodies against P. ovale occurs very frequently in AD, and rarely in patients with atopic disease without skin involvement.

Autoimmune mechanisms are thought to play a role in the pathogenesis of the chorioretinal changes in ocular onchocerciasis. In this study, the involvement of autoimmunity against retinal antigens in developing chorioretinitis was investigated. Serum levels of autoantibodies, directed against human S-antigen and interphotoreceptor retinoid-binding protein (IRBP), were determined in patients with onchocerciasis (n = 46) and endemic controls (n = 38) from Sierra Leone with the use of an enzyme immunoassay. In both groups high levels of anti-human S-antigen and IRBP antibodies were detected. No relationship could be demonstrated between the antiretinal antibody level and the occurrence of chorioretinitis in onchocerciasis. The levels of both anti-human S-antigen and IRBP antibodies were significantly higher in patients with onchocerciasis compared with endemic controls (P less than 0.001). Cross-reactivity of antiretinal antibodies with parasitic antigens could not be demonstrated as a possible explanation for the higher levels in patients with onchocerciasis. No correlation was found between the levels of antibodies of different classes against the crude Onchocerca volvulus, the egg antigen, or the microfilariae and the antiretinal antibody levels. Furthermore, in a panel of 13 different monoclonal antibodies directed against O. volvulus, only one showed a slight anti-human IRBP reactivity and none reacted with S-antigen. The immune response against the two retinal antigens investigated was not specific for onchocerciasis because high antibody levels were also found in patients with Bancroftian filariasis from Papua, New Guinea, and Surinam.(ABSTRACT TRUNCATED AT 250 WORDS)

Autoimmune reactions against retinal antigens have been suggested to play an important role in clinical uveitis in man. As yet the evidence for this assertion is very weak. Sympathetic Ophthalmia is a disease entity which comes closest to acceptance as an autoimmune disease although the autoantigen involved has not been identified. Both cellular and humoral autoreactivity against retinal antigens have been found both in uveitis patients as well as in healthy controls. Very high levels of retinal antibodies were found in onchocerciasis patients but no relation was observed with the occurrence of chorioretinitis. Differences were observed when testing patient sera against human or bovine retinal antigens (S-antigen or IRBP) emphasizing the need for using human tissue when investigating autoimmune responses. Circumstantial evidence in favor of an autoimmune etiology of uveitis include the morphology of the inflammatory infiltrate, effect of immuno-suppressive therapy and especially the establishment of experimental animal models. The experimental models of S-antigen or IRBP induced uveitis are primarily T cell mediated and also show pineal gland involvement. As yet no "established" human autoimmune disease has been described with a dominant role for T cells. Furthermore there is no evidence for pineal gland involvement in clinical uveitis. Analysis of the specificity of the T cell infiltrate or deposited immunoglobulins obtained from the diseased tissues may provide conclusive evidence for a possible autoimmune character of certain clinical uveitis entities.

The role of C1- inactivator (C1(-)-In) during activation of the classical complement pathway by soluble immune complexes was studied using purified human complement components C1, C4 and C1(-)-In, and stabilized soluble aggregates of normal human IgG as a model for soluble immune complexes. The C4-consuming ability that could be generated by incubation of precursor C1 with IgG aggregates was abolished completely by the presence of a large excess of C1(-)-In during the C1 activation step. Kinetic studies confirmed that this inhibition was due to a second-order reaction between C1- and C1(-)-In resulting in the irreversible inactivation of C1-. When aggregates of various sizes were enabled to induce C4 conversion in mixtures of C1, C4 and a variable concentration of C1(-)-In, the presence of C1(-)-In had two effects. Firstly, the efficiency of the aggregates in causing C4 consumption was reduced remarkably. At a C1(-)-In:C1 ratio of 8, which can be found in normal human serum, approximately eight to ten times as many aggregates were required for a given level of C4 consumption as when no C1(-)-In was present. Secondly, C1(-)-In diminished the maximum C4 consumption that could be achieved, especially with smaller aggregates. Thus, a complete or partial C1(-)-In deficiency probably facilitates complement activation by soluble immune complexes in two ways: it may enhance the efficiency of classical pathway activation by all C1-activating complexes, and it may enable small complexes, which normally cannot overcome the C1(-)-In barrier, to activate the classical pathway to the C4 level.

Although retinal S-antigen can induce experimental auto-immune uveitis in various animal species including primates, its role in clinical uveitis is not exactly known. More detailed knowledge on the immunoreactivity of human S-antigen might be of importance, since bovine S-antigen has been shown to carry both uveitogenic and non-uveitogenic epitopes. The number of immunoreactive epitopes on purified human S-antigen was therefore investigated in an inhibition ELISA with the use of a panel of four polyclonal and two monoclonal immune reagents. Assessment of their capacity to compete with each other for binding to the antigen resulted in complete, partial or no inhibition in the various combinations tested. Rabbit and rat anti-S-antigen immunoglobulins inhibited each other partially (up to 60%), from which the existence of at least three (groups of) epitopes was derived. Two monoclonal antibodies, of mouse (PDS-1) and rat (S.2.4C5) origin, did not inhibit each other, and thus defined two separate epitopes on human S-antigen. These epitopes belong to the set recognized by both rabbit and rat anti-S-antigen immunoglobulins since both monoclonals could be inhibited by rabbit and by rat antibodies. Epitopes detected by two mouse antisera also appeared to belong to this set. Thus, the existence of at least four immunoreactive sites on human S-antigen could be demonstrated.

A new hemolytic assay is described that specifically measures the precursor form of the C1s subcomponent of the complement system. The assay employs a C1s-depleted reagent obtained by immunoadsorption of fresh human plasma on immobilized goat anti-human C1s antibodies. Linear Z plots are obtained with nanogram levels of precursor C1s, whereas C1s completely fails to induce hemolysis in the assay. Because low concentrations of C1s do not interfere with the activity of precursor C1s, the assay can be used for the stoichiometric measurement of C1 activation. The precursor C1s assay was applied to the study of C1 binding and activation by soluble aggregates of human IgG (AIgG). Incubation of purified human C1 with AIgG caused a temperature-independent consumption of whole C1 hemolytic activity, indicating binding of C1, but almost no consumption of the total (precursor + activated) C1s activity. On the other hand, activation of C1, measured as the time- and temperature-dependent consumption of precursor C1s, could greatly exceed the binding of C1. These findings can be explained by using recent findings concerning the association-dissociation equilibrium between C1q and the tetrameric complex of C1r and C1s.

Retinal S-antigen is thought to play an important role in the immunopathogenesis of uveitis. To investigate whether S-antigen is a sequestered antigen confined to the retina, a sensitive ELISA was developed to determine the levels of this protein in various human ocular tissues, aqueous humour and serum. The ELISA was performed by incubating S-antigen-containing samples with solid-phase bound immunospecific rabbit anti human S-antigen F(ab')2 fragments and then incubating the bound S-antigen with mouse anti bovine S-antigen serum and the bound mouse antibodies with peroxidase-labelled rabbit anti mouse IgG; the peroxidase activity is developed with ABTS. This method was demonstrated to be highly sensitive and specific: S-antigen could be measured at concentrations of 5-10 nanograms per ml, irrespective of whether it was present in buffer, undiluted whole serum of tissue extracts. Human retinas were shown to contain approximately 1.2 mg immunoreactive S-antigen per retina. Of the other human ocular tissues, only the vitreous and choroid (including pigment epithelium) contained small amounts of S-antigen. Low levels of S-antigen could also be detected in the aqueous humour of two out of seven patients with posterior uveitis. No immunoreactive S-antigen could be detected in the serum of either healthy individuals or patients with uveitis. Sera collected from diabetic patients 15 minutes after extensive laser photocoagulation also did not contain immunoreactive S-antigen. Preliminary experiments with rats to study the clearance of intravenously injected S-antigen from the circulation indicated that the relatively short half-life (+/- 30 min) of circulating S-antigen might account for the absence of detectable S-antigen in the patient sera.

The effect of human erythrocytes (E) on blastogenesis and immunoglobulin (Ig) production induced by pokeweed mitogen (PWM) in cultures of human peripheral blood mononuclear cells (PBMC) was investigated. The stimulation of PBMC with PWM was markedly enhanced in the presence of E, and PWM bound to E, followed by thorough washing (E-PWM), was even more effective in inducing blast cell formation and Ig production. Blast cell responses after stimulation with E-PWM were on average two times higher than those seen after stimulation with comparable dilutions of fluid-phase PWM. The PWM that remained in solution after incubation with E (Sup E-PWM) had little mitogenic capacity and inhibited the blast cell response induced by fluid-phase PWM. Transwell culture experiments demonstrated that the enhancement of the blast cell response of PBMC by E-PWM could be induced by PWM that was released from E-PWM, whereas the enhancement of Ig production was found to be dependent on the presence of PWM on E. Both for blast cell formation and Ig production, it was found that the enhanced stimulation with E-PWM depended on the presence of monocytes.

The influence of IgM-rheumatoid factor (IgM-RF) on the activation of isolated C1 by soluble IgG aggregates (AIgG) and immune complexes was studied. IgM preparations obtained from the sera of four patients with seropositive rheumatoid arthritis markedly reduced the C1 activation capacity of AIgG, especially when large aggregates were tested. The results of parallel experiments with radiolabelled AIgG indicated that this inhibitory effect of IgM-RF was accompanied by a very large increase of the aggregate size. A comparable IgM preparation isolated from pooled normal human serum influenced neither the size nor the C1 activation capacity of AIgG. The inhibitory effect of IgM-RF on C1 activation was also demonstrated for soluble tetanus-anti-tetanus immune complexes. Thus, in spite of the established C activation ability of IgM-RF and the fact that, in general, larger IgG aggregates and immune complexes activate C1 more efficiently, cross-linking and size enlargement of soluble IgG complexes and aggregates by IgM-RF lead to a decrease of the C1 activation capacity. As a consequence, IgM-RF may reduce plasma complement activation by soluble IgG complexes in the circulation of patients with seropositive rheumatic diseases.

Purified human retinal S-antigen (S-ag) was used to investigate the occurrence of humoral and cellular autoimmune reactions against S-ag in uveitis patients. With a sensitive ELISA method anti-S-ag antibodies could be detected in the sera of 28% of the uveitis patients. No difference was found between patients with posterior or panuveitis (31 out of 117 positive) and patients with anterior or intermediate uveitis (16 out of 52 positive). Similar frequencies and levels of anti-S-ag autoantibodies were also found among healthy controls (6/20) and patients who had undergone cataract surgery (6/17). Immunoblotting with purified S-ag and with whole human retinal extract confirmed the presence of anti-S-ag antibodies in uveitis and control sera. Moreover, antibodies against various other retinal proteins could also be demonstrated in patients and controls, without being particularly enhanced in uveitis. The cellular immune responsiveness was tested by measuring the production of migration inhibitory factor (MIF) during overnight culture of peripheral mononuclear cells with the antigen. None of 18 healthy controls responded, whereas 17 positive reactions were observed in the group of 44 uveitis patients. The highest frequencies were found in patients with posterior (5/12) or pan- (7/12) uveitis, while of the responders with anterior (2/8) or intermediate (3/12) uveitis, three had disorders affecting the retina. Thus, cellular autoimmune responsiveness to S-ag is apparently associated with posterior and pan-uveitis, and might also occur in non-uveitic retinal disorders, whereas the occurrence of anti-S-ag antibodies is probably not at all pathognomic for uveitis.

The capacities of soluble human and rabbit IgG aggregates to bind and to activate human C1 were compared. Aggregates prepared by incubation of purified IgG at 63 degrees C were fractionated by gel filtration and hemolytic assays were used to measure the binding and activation of isolated human precursor C1. The C1 binding and activation capacities of both human and rabbit IgG aggregates were highly dependent on their size. Human IgG aggregates had a slightly higher binding avidity for human C1 than rabbit IgG aggregates of comparable size, but no clear differences were found between their capacities to activate C1. Experiments with nonaggregated IgG also indicated that although human IgG binds human C1 somewhat more avidly, human and rabbit IgG do not differ in their capacities to initiate fluid-phase activation of the human classical complement pathway.

The interaction between small aggregates of human IgG and the first component of human complement was studied. Stabilized soluble IgG aggregates of restricted size were prepared by heat aggregation of human IgG, followed by sucrose-density ultracentrifugation. Human C1 was isolated in its precursor form by euglobulin precipitation, followed by gel filtration and immunoadsorption. A C1 preparation was obtained of which more than 90% was still in its unactivated form. Soluble aggregates containing 20, 10 or 5 molecules IgG, and monomeric IgG were tested for their ability to bind and to activate C1. The binding of C1 was determined by C1 consumption, whereas the activation of C1 was measured as the increased ability of the C1 preparation to consume purified human C4 after the incubation with the aggregates. The three aggregates tested and monomeric IgG were all able to bind and to activate C1, but the efficiency of both processes markedly increased with increasing aggregate-size. Furthermore, it was found that all four preparations activated an appreciable amount of C1 at concentrations that did not result in any detectable C1 fixation. These results confirm earlier suggestion that C1 can be activated during a short, transient binding to small aggregates or immune complexes that have a low avidity for C1, after which the activated form, C1, is released into the medium.

The interaction between soluble immune complexes and the first component of complement (C1) was studied. Complexes were prepared from purified bovine thyroglobulin (BTg) or tetanus toxoid (TT) and immunospecific IgG antibodies. Purified human precursor C1 was incubated with dilutions of the preparations, and the inhibition of C1 haemolytic activity was determined as a measure of C1-binding. The activation of C1 was assessed by measuring the amount of C4 consumed by generated C1. The molar antibody/antigen (Ab/Ag) ratio of BTg--anti-BTg mixtures strongly influenced their C1-binding and C1-activating capacities: mixtures with high Ab/Ag ratios were by far the most efficient. On the other hand, the Ab/Ag ratio had only a limited influence on the activity of TT--anti-TT complexes. The effect of complex size was investigated by ultracentrifugation of antibody-antigen mixtures on calibrated sucrose density gradients followed by C1-binding and -activation experiments with the fractions obtained. For both types of immune complex, the C1-binding and -activating capacities increased markedly with increasing complex size. Thus, both the size and the Ab/Ag ratio of soluble immune complexes influence their capacity to activate the classical complement pathway. The effect of the Ab/Ag ratio, however, may also be dependent on the antigen molecule(s) present in the complexes.

Immunofluorescence on polymorphonuclear cells (PMN) of patients with Felty syndrome (FS) revealed increased amounts of IgG, IgA, and IgM bound to the PMN surface compared with PMN of patients with rheumatoid arthritis alone. A positive correlation was found between the score for surface-bound immunoglobulins on FS-PMN and the results of the Clq binding assay in FS sera. After preincubation with sera from 20 patients with FS, immunofluorescence on PMN from healthy controls (HC) showed that these cells had bound IgG, IgA, and IgM. However F(ab')2 fragments of IgG from FS sera did not bind to PMN, although the antigen-binding reactivity of the F(ab')2 fragments was maintained as shown by control experiments. Immunoglobulins eluted from FS-PMN failed to bind to HC-PMN, whereas the corresponding IgG of patients with autoimmune neutropenia was bound. Gel filtration of FS sera on Sepharose 4B showed that the binding of IgG in FS sera to PMN did not coincide with the 7S peak but occurred mainly in fractions containing larger material. No binding of IgA and IgM to HC-PMN was found after incubation with FS sera pretreated with polyethylene glycol (PEG) to precipitate immune complexes. These results indicate that in sera of patients with FS the PMN-binding reactivity of IgG, IgA, and IgM is due to the binding of immune complexes containing these immunoglobulins and not to presence of autoantibodies directed to antigens on the neutrophil surface.

Spontaneous production of immunoglobulins (Igs) by peripheral blood mononuclear cells (PBMC) in vitro was investigated to assess B cell activity in a group of 24 patients with rheumatoid arthritis (RA) with or without active joint disease and with or without rheumatoid vasculitis (RV) at the time of study. PBMC of patients with active arthritis (Ritchie index above 16) produced significantly more IgG and IgA than those of patients with inactive joint disease or those of 12 healthy controls. Enhanced production of IgG was found mainly among RA patients with concomitant RV, whereas markedly enhanced IgA production could also be found in patients without symptoms of RV. IgM production was only enhanced in two patients who had both active arthritis and RV. High production of IgG and IgA was probably due to increased numbers of Ig-secreting cells among freshly isolated PBMC, since the concentrations of Ig produced in vitro rose steadily, starting on day 0 and persisting throughout the entire culture period. Moreover, IgG and IgA concentrations measured after 7 days of culture showed significant correlations with the numbers of IgG- and IgA-containing plasma cells in PBMC on day 0. Comparison of the spontaneous production of Igs by PBMC with the levels of circulating immune complexes (CIC), showed that CIC levels were also significantly higher in active arthritis and in RV, but that there was no correlation between the CIC levels in individual patients and Ig production by their PBMC in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)

In this study we report on the preparation and application of pokeweed mitogen (PWM) conjugated to latex particles. This conjugate (PWM-latex) was prepared by incubation of PWM with latex particles in the presence of glutaraldehyde. The effect of the addition of PWM-latex to human peripheral blood mononuclear cells (PBMC) was fully comparable to the addition of PWM alone i.e. differentiation of lymphocytes into blast cells followed by proliferation of these blast cells as measured by DNA synthesis and total cell number. Electronmicroscopically PWM-latex was found to be taken up by monocytes within the first 24 h after addition. Although no direct interaction could be observed between PWM-latex and lymphocytes, the latter were found to differentiate into blast cells. Due to interactions of these blast cells with latex-containing monocytes, latex particles were obviously released from the phagocytes and close contacts between latex particles and blast cells were regularly seen. In addition, it was found that blast cells of T cell origin, as judged by their positive reaction with anti-T cell monoclonal antibodies, had taken up latex particles. Based on enzyme-cytochemical, functional and light microscopical studies, monocytes could not be detected in the PWM-latex-driven PBMC stimulation after 6 days. At the electronmicroscopical level evidence was found that the inability to demonstrate macrophages could be due to the release of the lysosomal enzyme content and of parts of the cytoplasm.

The reactions of human and bovine retinal S-antigen (S-ag) with polyclonal rabbit antibodies were compared in ELISA, immunoblotting and inhibition ELISA. Titrations in ELISA with plastic-adsorbed S-ags revealed that the great majority (70-100%) of human S-ag epitopes and anti-human S-ag antibodies were cross-reactive. In contrast, the cross-reactivity of bovine S-ag (25%) and anti-bovine S-ag antibodies (15-20%) indicated an important contribution of species-specific epitopes to the antigenicity of bovine S-ag. Immunoblotting of S-ag fragments after treatment with chymotrypsin confirmed these differences and also demonstrated different chymotrypsin-induced cleavage patterns of human and bovine S-ag. Thus, in assays involving partial denaturation and/or degradation of the antigens, human S-ag showed little, and bovine S-ag a marked species-specific immunoreactivity. In inhibition ELISA however, in which S-ags in solution could be studied, species-specific reactions strongly predominated for both S-ags. Anti-human S-ag and anti-bovine S-ag antibodies could be absorbed with nM concentrations of fluid phase human and bovine S-ag, respectively, whereas in both cases the cross-reacting antigen had no detectable inhibitory potential. The epitopic structures of human and bovine S-ag in solution may thus be largely different.