Stimulation of murine B lymphocytes by isolated C3b

Different stimulating effects of complement C3b and complete Freund's adjuvant on antibody response

Upon activation, complement C3 undergoes a conformational change and acquires the capacity to covalently bind to other proteins such as antigen and to interact with specific receptors; therefore, C3 is involved in cell mediated immune response. The adjuvant effect produced by linking C3-fragments to antigen has recently been described. We injected C3b-Ag complexes consisting of one molecule of C3b ester linked to one molecule of HEL to immunised mice, and we compared the C3b adjuvant activity with that of complete Freund's adjuvant. IgG titers elicited by HEL emulsified in CFA (HEL + CFA) were higher than those elicited by HEL-C3b, but decreased rapidly after a peak response around day 45 whereas HEL-C3b resulted in a continuous increase of anti-HEL response. Mice immunised with HEL + CFA then boosted with HEL-C3b gave significantly higher response than those boosted with HEL + CFA, indicating more efficient memory cell restimulation by C3b. HEL + CFA leads to better priming than HEL-C3b when mice are boosted with HEL-C3b. Thus, adjuvant effect of C3b is different from that of CFA, leading to more stable IgG production and better memory stimulation.

Amplification of the Antibody Response by C3b Complexed to Antigen Through an Ester Link

Complement C3 has been described as playing an important role in the cell-mediated immune response. C3b has the capacity to covalently bind Ag and then to stimulate in vitro Ag presentation to T lymphocytes. To verify this observation in vivo, we prepared and purified covalent human C3b-Ag complexes using lysozyme (HEL) as Ag. The characterization of these HEL-C3b complexes indicates that they are representative of those susceptible to be generated in physiological conditions. Mice were immunized with 0.1 to 0.6 μg of either free HEL, HEL + C3b, HEL-C3b, or HEL + CFA. Response was assessed after two i.p. injections by quantification of specific Ab production. Immunization with either HEL-C3b complexes or HEL + CFA leads to anti-HEL IgG production whereas free HEL or HEL + C3b was ineffective. Either HEL-C3b or HEL + CFA immunizations led to a similar Ig subclasse patterns, including IgG1, IgG2a, IgA, and IgM.

Our experiments provide the first evidence for modulation of specific Ab response by C3b when it is bound to Ag through a physiological-like link. Taken together with previous data concerning Ab response following recombinant HEL-C3d immunization, cellular events such as processing of C3b-Ag by APC and recognition by T lymphocytes, this present result underlines the importance of C3b and its fragments in stimulation of the immune system, through the multiplicity and complementarity of its interactions.

Co-expression and secretion of C3, the third component of complement and a C3-cleaving cysteine proteinase in a highly metastatic human melanoma cell line

We recently demonstrated that DM-4, a human melanoma cell line highly metastatic in nude mice, expressed a p41 C3-cleaving proteinase. This p41 proteinase is a cysteine proteinase, associated to cell surface and involved in tumorigenicity and metastatic properties of these tumor cells. We demonstrate herein that DM-4 cells also secrete the p41 proteinase. In addition, analysis of cellular components which reacted with the p41 proteinase led us to demonstrate that DM-4 cells synthesized and secreted human C3. Secreted C3 is cleaved by the secreted p41 proteinase and a C3dg-like fragment is generated. This is the first demonstration that a human melanoma cell line co-expresses and co-secretes human C3 and a C3-cleaving cysteine proteinase, antigenically related to procathepsin L.

Determination of soluble CD21 as a parameter of B cell activation

In this study we established a novel solid-phase immunoassay for CD21 using the time-resolved fluorescence of lanthanide chelates. The capture assay was able to detect concentrations of as low as 100 pg of CD21 antigen per millilitre of sample and was used for quantitative determination of CD21 in lysates of different cell lines as well as in patient serum specimens. CD21 was measured in lysates of tonsils and cell lines of B, T cell and myelomonocyte lineage, and appeared to consist of monomeric antigen under the detergent conditions used. Elevated levels of soluble CD21 were observed in serum of patients with Epstein-Barr virus (EBV) infection, a disease known to be associated with polyclonal B cell activation, and in infection with the lymphotropic rubella virus. Significantly increased levels were also found in malignancies which are associated with EBV. In patients with nasopharyngeal carcinoma (NPC), a correlation with the titre of EBV-specific IgA was observed, thus supporting a possible role of soluble CD21 as a marker for disease activity in certain malignancies. Our data suggest that measurement of soluble CD21 could serve as a marker for activation of the immune system and diseases involving the B cell lymphoid system. Possible mechanisms and functions of soluble CD21 are discussed.

A 16 amino acid synthetic peptide derived from human C3d triggers proliferation and specific tyrosine phosphorylation of transformed CR2-positive human lymphocytes and of normal resting B lymphocytes

We demonstrate herein that p16, a 16 amino acid synthetic peptide derived from human C3d, which carried LYNVEA sequence of C3d reacting with CR2 and C3d present in trypsin-cleaved C3, triggered "in vitro" and "in vivo" phosphorylations and "in vitro" proliferation of human B lymphocytes, depending on the stage of cell differentiation. Indeed, p16 and C3dT induced "in vivo" tyrosine phosphorylation of pp105 and "in vitro" proliferation only of CR2-positive and not of CR2-negative cell lines. In addition, p16 and C3dT also induced "in vivo" tyrosine phosphorylation of pp100 and "in vitro" proliferation of only small dense resting B lymphocytes and not other B lymphocyte subpopulations nor T lymphocytes. These data suggest that induction of pp100 and pp105 phosphorylation by p16 and C3dT could represent an early event associated with expression of CR2 in the regulation of human B lymphocyte proliferation.

Immunomodulating effects of serum-material interactions

The objective of this study is to evaluate an in vitro model to assess the effects of serum-material interactions on complement activation, macromolecular adsorption, and lymphocyte response. Minifilters of clinically available materials (PVA, EVAL-4A, and EVAL-D) used in extracorporeal therapies were evaluated. The test circuit consisted of a pump, sterile tubing, collection vessels, and the minifilter. A sham circuit similar to the test circuit was constructed, but without the filter. Serum flow rates and volumes processed were scaled down to those of clinical use. Post PVA serum showed the highest degree of complement activation, macromolecular solute adsorption, and lymphocyte suppressive response when incubated with Con-A, PHA, PWM, and Candida. Post EVAL-4A sera enhanced the response of lymphocytes to Con-A and PHA, while Post EVAL-D sera showed a slight suppression to these mitogens. Blood-material interactions have been shown to cause blood cellular changes. The in vitro model employed is simple to apply and does not require an animal or patient. The membrane modules used are a mini-type of clinically available extracorporeal filters, and there is a greater direct relevancy to clinical applications than there would be using specially formulated materials. This system would provide useful preclinical information in evaluating the effect of serum-material interactions.

A 16 amino-acid synthetic peptide, derived from human C3d, carries regulatory activity on in vitro phosphorylation of a cellular component of the human B lymphoma cells, Raji

We present herein the first evidence that human C3 and, with a higher efficiency, trypsin-cleaved C3 enhanced in vitro phosphorylation of a cellular component, characterized by an apparent molecular weight of 105 kDa, pp105, present in the human B lymphoma cells, Raji. This regulatory activity was associated with C3d fragment generated in trypsin-cleaved C3. A 16 amino-acid peptide, carrying the LYNVEA sequence of C3d reacting with the C3d receptor (CR2), was synthetized. P16 enhanced, in a dose-dependent curve between 0.3 to 10 microM, in vitro phosphorylation of pp105, as well as C3d fragments present in trypsin-cleaved C3. A fibrinogen-related synthetic peptide of 15 amino acids, used as control, had no effect on pp105 phosphorylation. P16 and trypsin-cleaved C3 regulate pp105 phosphorylation through identical pathways. Thus, p16 represents the 16 amino-acid sequence of C3 which regulated in vitro phosphorylation of pp105.

Quantification of non-activated (native) complement component C9 synthesized by alveolar macrophages from patients with sarcoidosis

Alveolar macrophages (AM) from sarcoidosis patients synthesize the functional alternative and terminal pathways of complement, and increased complement production may be one of multiple factors in the pathogenesis of sarcoidosis. We thus examined whether AM from sarcoidosis patients produced quantitatively more C9 in vitro than AM from healthy controls. AM from 16 patients with active sarcoidosis and seven healthy controls were cultured under serum-free conditions for 6, 12, 24, 48, or 72 h. A quantitative production of C9 was found in the harvested medium in 10 of 16 sarcoidosis patients. There were no detectable levels of C9 in the seven controls. Activated C9 was found in all patients and in the majority of the controls. C9 was quantified by an enzyme immunoassay based on a monoclonal antibody (M1) to non-activated C9. Our results indicate greater production of C9 by sarcoidosis AM than by their healthy counterparts.

Synthesis of complement by alveolar macrophages from patients with sarcoidosis

Sarcoidosis is a granulomatous disorder of unknown aetiology. Alveolar macrophages (AM) in sarcoidosis release a variety of mediators important to the pathogenesis of the disease. Complement is essential for the inflammatory response and we investigated whether there were any major defects in the potential for sarcoidosis AM to synthesize complement in vitro. AM from 11 patients with active sarcoidosis and three healthy controls were cultured under serum-free conditions. There was a significant binding of polyclonal (anti-C5, -C6, -C7, -C8) and monoclonal anti-complement antibodies (anti-C3c and anti-C9 neoepitope (aE11] to agarose beads incubated with unstimulated AM for 24, 48, or 72 h. A significant and inhibitable production of soluble C3c, C5, C9, and S-protein was found in the harvested medium as detected by enzyme immunoassays. Activated C3 and C9 were also detected based on neoepitope expression. Presence of co-cultured agarose beads reduced the amount of soluble S-protein due to deposition on the agarose. We argue that the C9 neoepitope is an integral part of the terminal complement complex (TCC), both in the fluid and solid phase when bound to the agarose. In the fluid phase, SC5b-9 was generated, whereas the agarose-bound S-protein is assumed not to be associated with TCC on the beads. The results demonstrate for the first time that AM from sarcoidosis patients synthesize the functional alternative and terminal pathway of complement.

The role of prostaglandins in C3a-mediated suppression of human in vitro polyclonal antibody responses

Suppression of polyclonal antibody responses in human peripheral blood mononuclear cell cultures by human C3a appears to involve the release of endogenous prostaglandins from monocytes. C3a was found, under the experimental conditions employed, to activate the cyclooxygenase pathway of arachidonic acid metabolism with the release of large amounts of the prostaglandin E2 species. Suppression of the protein A-induced polyclonal antibody response by C3a is abrogated by the prostaglandin synthesis inhibitor indomethacin. In addition, physiologic amounts of exogenous PGE2 were able to inhibit polyclonal antibody secretion in a manner similar to the suppression observed when C3a was added to culture. These results suggest that C3a-induced release of prostaglandins could be a major element in immunosuppression induced by C3a.

Involvement of complement in B-cell, T-cell and monocyte/macrophage activation

In the early 70's it had been shown, that for the immune response against T-dependent antigens C3 was necessary, while T-independent antigens, although activating the alternative pathway of complement, triggered antibody formation also in C-deficient mice. During recent years functional and biochemical knowledge about complement binding structures on B-cells and monocytes/macrophages continuously increased and, also, on T-cells C3 binding entities have been detected. In the case of B-cells and, at least in special experimental conditions, in the case of T-cells C3 can exert a proliferative response as long as the cells are prestimulated (excited) by anti-Ig or IL-2, respectively. Monocytes can bind C3b- or iC3b-carrying particles, but only when progressed to macrophages can they phagocytose such particles. Thus the concept evolves that B-cells, T-cells and monocytes can acquire competence for a C3-driven response when excited properly. The involvement of molecules such as CR1, CR2, factor H, IL-2-receptor and others with a basic structure of repeating units of 61 amino acids in the triggering processes is a surprising finding and certainly suggests their functional importance. In the case of T-independent antigens the structures triggering the alternative pathway of complement are the structures triggering monocytes directly. Whether these two functions have a causal relationship has to be shown.

Cell cycle control of activated, synchronized murine B lymphocytes--roles of macrophages and complement C3

Three restriction points control the cell cycle of activated murine B lymphocytes in a synergistic way. The first is controlled by the occupancy of surface immunoglobulin either by antigen- or by immunoglobulin-specific antibodies. The second is controlled by the complement C3d receptor CR2 which can be occupied by cross-linked C3b or C3d to stimulate the entry into S phase, or by soluble C3d or a C3 alpha-chain peptide, binding to the CR2 receptor, which inhibit the entry into S phase. Macrophages produce so-called alpha factors which also control the B-cell cycle at the same point. Thus, it is suspected that macrophages produce components of the early pathway of complement activation which finally lead to cross-linking of CR2 receptors on B cells. The third restriction point is controlled by unknown receptors that recognize so-called beta factors produced by helper T lymphocytes.

Receptors for the third component of complement: their association with maturation stage in non-Hodgkin lymphomas (NHL) and their possible implication with the development of follicular structures

In the majority of 188 non-Hodgkin lymphomas (NHL) investigated in this study, we found a simultaneous expression of the receptors for c3b and c3d (CR1 & CR2; cccorr = 0.69, P less than 0.0005). An analysis of the different histological entities of the Kiel classification revealed that this coexpression was most pronounced for germinal centre-derived (cccorr = 0.63, P = 0.0004) and immunocytic NHL (cccorr = 0.86, P = 0.0024), whereas in chronic lymphocytic leukaemias there tended to be a more heterogeneous pattern of complement receptor (CR) expression (cccorr = 0.29, P greater than 0.10). In contrast to these NHL of mid B cell stage, most of the NHL of early (i.e. acute lymphocytic leukaemia, lymphoblastic NHL) and late B cell stage (i.e. hairy cell leukaemia, immunoblastic NHL, multiple myeloma) did not express either of these receptors. CR positive NHL often showed a follicular arrangement of the neoplastic cells and had higher numbers of T helper/inducer (T4) lymphocytes (PCR1 less than 0.00005, PCR2 less than 0.05). Some cases of mid B cell NHL and all cases of hairy cell leukaemia reacted with antibodies against CR3 (i.e. the ic3b receptor).

Eosinophil-mediated cellular cytotoxicity induced by zymosan-activated serum

The aim of the present work was to develop an in vitro model of eosinophil cytotoxicity which mimics numerous in vivo situations characterized by complement activation through the alternative pathway. Our results demonstrate that eosinophilic granulocytes from patients with parasitic diseases and blood eosinophilia were able to damage chicken red blood cells when incubated with zymosan-activated serum (ZAS) as assessed by a 51Cr release assay. The phenomenon was independent of the presence of antibodies directed against the target cells and related to the quantity of ZAS added to the wells. As target cell lysis is totally or partially inhibited by catalase, sodium azide and potassium cyanide, an involvement of toxic oxygen derivatives as cytolytic mediators was suggested.

Regulation of human cytotoxic responses by complement: C3, C3b and C3d preparations enhance human allogeneic cytotoxic responses

Complement components and complement breakdown products have been found to participate in the regulation of the immune response. In the present study we investigated the effect of C3 and its fragments, C3b, C3c and C3d on human allogeneic cell mediated lympholysis (CML). C3 and C3b at a concentration of 275 M X 10(-9) and C3d at a concentration of 330 M X 10(-9) enhanced human allogeneic CML by at least two fold. In contrast C3c did not affect CML responses. Both C3b and C3d had to be present at the initiation of the cultures in order to exert their effect. Similar doses of C3b and C3d did not affect the mixed lymphocyte responses (3H-thymidine uptake) while higher doses were clearly inhibitory. None of the preparations induced proliferative or cytotoxic responses in the absence of allogeneic stimulating cells. C3b and C3d added to the mixed lymphocyte cultures caused increased production of interleukin 2. We conclude that C3b and C3d facilitate allogeneic cytotoxic responses through increased production of interleukin 2.

Human C3a-mediated suppression of the immune response. II. Suppression of human in vitro polyclonal antibody responses occurs through the generation of nonspecific OKT8+ suppressor T cells

C3a-mediated suppression of Ig secretion in human PBL cultures occurs through the activation of suppressor T cells. Incubation of T cell-enriched populations derived from peripheral blood or tonsil results in the activation of nonspecific OKT3+8+ suppressor T cells capable of inhibiting Fc fragment-induced Ig secretion in fresh autologous PBL cultures. Generation of OKT8+ suppressor T cells by C3a requires the interaction of T cells, adherent cells, and C3a. Activation of the suppressor-T-cell pathway is initiated early in culture. Incubation of the T-cell-enriched populations with C3a for 0.5 hr results in functional, transferable suppressor cells. Maximum suppression was achieved when C3a was allowed to interact with the cell population for 1-2 hr.

Growth control of activated, synchronized murine B cells by the C3d fragment of human complement

Three restriction points control the cell cycle of activated B lymphocytes. The first occurs directly after mitosis and is controlled by the occupancy of surface-bound immunoglobulin. The second is observed approximately 4 h after mitosis in the G1 phase of the cycle, that is, before DNA replication, and is controlled by growth factors that are produced by macrophages which we have previously classified as alpha-type factors. The third restriction point occurs in the G2 phase, 2-4 h before mitosis, and is controlled by beta-type growth factors probably produced by helper T lymphocytes. The third component of complement, C3, has long been implicated in the control of B-cell responses. C3 is secreted by monocytes and macrophages. We have found recently that crosslinked, but not soluble, human C3 stimulates activated, but not resting, murine B cells to thymidine uptake. Here we investigate the role of C3b and C3d in the progression of the cell cycle of activated, synchronized murine B cells. We find that crosslinked C3d replaces the action of alpha-factors within the cell cycle of these cells and allows entry into S phase. In contrast, soluble C3d inhibits the action of alpha-factors. This implies that a C3d-specific receptor, probably the murine analogue to the human complement receptor CR2, is a growth factor receptor on activated B cells that will give the cell a growth-positive signal when it is crosslinked, while occupancy by the soluble form of C3d will result in inhibition of the action of alpha-factors or of crosslinked C3b or C3d. A stretch of weak homology between the cDNA sequence of murine C3d and those of murine growth factors indicates that an insulin-like growth factor could be the active principle of C3d that controls the cell cycle of activated B cells.

Regulation of immunoglobulin secretion by factor H of human complement

As human B lymphocytes and macrophages carry surface receptors for Factor H (B1H), we investigated the possibility that this complement component regulates their function. Factor H inhibits immunoglobulin secretion by peripheral mononuclear cells (MNC) stimulated with pokeweed mitogen if present at the initiation of the cultures and at concentrations greater than 50 micrograms/ml. Factor H also inhibited stimulation and differentiation of purified B cells into immunoglobulin-secreting cells by Epstein-Barr virus (EBV). The inhibitory effect of Factor H was abrogated if anti-Factor H antibody was present in the cultures. EBV-transformed B-cell lines secreted less immunoglobulin if Factor H was present in the culture for at least 4 days. Culture of MNC with Factor H did not lead to the generation of suppressor T cells or macrophages. In contrast, Factor H did not cause proliferation of human peripheral total MNC or enriched T-cell or B-cell subpopulations. Also, Factor H did not inhibit the proliferation of MNC in response to several mitogens and antigens. Our results strongly indicate that Factor H is able to block human B-cell differentiation in vitro without blocking the proliferative ability of the cells. Factor H seems to act directly on the B cells through its receptor on their surface, since it inhibited T-dependent and T-independent B-cell differentiation but generated no suppressor cells.

The change in C3b receptors on erythrocytes from patients with systemic lupus erythematosus

A deficiency of C3b receptors (CR1) on erythrocytes from patients with systemic lupus erythematosus (SLE) has already been reported and assumed to be one of the causes of the impaired immune complex clearing function found in these patients. In the present study, we developed a functional assay to quantify the amount of CR1 on human erythrocytes. Sample erythrocytes were reacted with tetanus toxoid-anti-tetanus toxoid immune complexes (IC) in the presence of complement. The amount of CR1 was expressed as the amount of IC bound to sample erythrocytes. Determination of CR1 showed a decrease in erythrocytes from patients with SLE, rheumatoid arthritis and other connective tissue diseases. The activity of CR1 in erythrocytes from patients with SLE changed in parallel with complement activity and also reflected the clinical status of two of three patients. These results imply that the reduction of CR1 found in SLE patients might be cause not only by hereditary factors but by unknown factors that influence the amount or function of CR1.

The action of human C3 in soluble or cross-linked form with resting and activated murine B lymphocytes

The third component of complement C3 has been implied in the stimulation of B lymphocytes to proliferation and maturation for Ig secretion. We have reinvestigated the extent of this activation with either activated or resting murine splenic lymphocytes in serum-substituted cultures. Human C3 was used in either soluble or cross-linked form. Soluble as well as Sepharose-bound or glutaraldehyde-cross-linked C3, over a range of concentrations, was inactive with resting splenic lymphocytes of (C57BL/6J X DBA/2)F1, C3H/HeJ and C57BL/6J nu/nu mice. However, lipopolysaccharide-activated spleen cells, enriched for B cell blasts, were stimulated by immobilized and cross-linked C3, while they did not respond to soluble C3. The extent of restimulation was comparable to that induced by lipopolysaccharide and resulted in both increased proliferation and maturation to Ig-secreting cells. The stimulation of the blast cells appears to be C3 specific, since it can be inhibited by free C3.

Protein A and staphylococcal products in neoplastic disease

Tumoricidal responses and tumor regressions have been observed after plasma perfusion over Staphylococcus aureus Cowan I (SAC), or purified protein A immobilized on solid supports. This system was initially studied in a single human patient and then extended to dogs with spontaneous mammary carcinoma, an excellent model of human breast cancer. In the single patient and dogs with mammary tumors, perfusion of plasma over protein A bearing staphylococcus resulted in tumor necrosis and tumor regression. Tumor reduction or growth retardation with similar perfusion systems has been noted in various feline and rodent tumor models. Tumoricidal responses were also observed in canine tumors after perfusion over commercial protein A which was immobilized in a collodion charcoal matrix (PACC). These responses were amplified when a subtherapeutic and nontoxic dose of cytarabine was given after perfusion. Similar tumor reduction in murine and feline tumor models has been noted after perfusion of autologous serum over protein A immobilized on various other solid supports. The PACC perfusion system was extended to five consecutive patients with advanced breast adenocarcinoma. Four of five patients showed tumor regression after perfusion of small volumes of autologous or homologous plasma over PACC. Patients also experienced pyrexia, nausea, vomiting, and significant cardiopulmonary toxicity. Detailed hemodynamic studies of these effects showed that the major pathophysiology involved a decline in total peripheral resistance associated with an increase in cardiac output. With reduction of immobilized protein A quantity and diminution in plasma perfusion rate, the cardiopulmonary toxicity associated with treatments was diminished. Chemotherapy given as FAC to a single patient shortly after concluding perfusion therapy resulted in rapid regression of residual large tumor masses. Studies focusing on the mechanism of the tumoricidal responses have examined changes in sera after incubation or perfusion over immobilized SAC or PACC. Major findings include (1) the identification of protein A leaching from PACC and SAC after serum perfusion and appearing in the effluent as Clq binding oligomers composed predominantly of IgG and protein A but also containing IgA, IgM and C3 with a molecular weight range of 600,000 to 2,000,000; (2) the identification of C3a anaphylatoxins in serum perfused over PACC or SAC; (3) the recognition that several enterotoxins, in particular enterotoxin B are present in commercial protein A preparation.(ABSTRACT TRUNCATED AT 400 WORDS)

Enhancement of human B cell proliferation by an antibody to the C3d receptor, the gp 140 molecule

The C3d receptor is a specific marker of B lymphocytes. Recently we have shown that C3d receptor activity is carried by a gp 140 membrane antigen. A polyclonal antibody has been prepared by immunizing a rabbit with highly purified gp 140 molecule isolated from membranes of the human B lymphoblastoid cell line Raji and its high specificity was previously demonstrated. We tested the effect of this antibody to the C3d receptor on the B cell proliferative response. Purified B cells from human blood were induced to proliferate by a B cell growth factor (BCGF)-containing partially purified supernatant from activated T cells. The anti-C3d receptor F(ab')2 enhanced the BCGF-dependent B cell proliferation. This effect was dose dependent, was observed in the presence of different concentrations of BCGF and did not correspond to a change in the time course of the response. The anti-C3d receptor F(ab')2 had no mitogenic effect in the absence of T cell supernatant. In contrast the undigested anti-C3d receptor IgG suppressed the BCGF-dependent B cell proliferation. These results emphasize the potentialities of anti-gp 140 F(ab')2 to explore the involvement of the C3d receptor in the regulation of B cell response to T cell products.

Characterization of the third component of pig complement and its utilization in a C3b receptor study

The third component of the pig complement system (C3) was isolated in hemolytically active form and characterized. The C3 component is a beta-globulin with the molecular weight of 191,000 and is composed of 2 non-identical polypeptide chains of Mr 112,000 and 74,000. The isolated C3 can be used for the detection of the C3b receptor on the membranes of heterologous peritoneal macrophages.

Sera used for complement-mediated cytolysis can alter B cell function in vitro

Nonspecific effects of reagents used to selectively isolate lymphocyte subpopulations are most often analyzed according to their influence on cell viability and proliferation. While characterizing monoclonal anti-human B cell antibodies, we detected consistent changes in B cell function between individual donors, no matter which antibody was employed to deplete B cell subpopulations. The source of these alterations was traced to the commercial complement-containing sera used for cytolysis. Different lots of serum from 3 separate commercial vendors and 2 animal species (rabbit and guinea pig) routinely altered B lymphocyte differentiation after stimulation with either pokeweed mitogen or Staphylococcus aureus (Cowan I), while cell viability, lymphocyte subpopulation distribution, and proliferative responses were unaffected.

Mechanisms of leukocyte regulation by complement-derived factors

Progress over the past five years has drawn attention to the fact that the anaplylatoxins are important factors in both leukocyte activation and regulation events. The C5 anaphylatoxin has been proposed to play major role in leukocyte aggregation and adherence phenomenon. Influences of C5a on the leukocyte may lead to clinical manifestations such as respiratory distress syndrome after trauma or postpump syndrome after cardiopulmonary bypass, both effects derived from leukocyte sequestration. Many other clinical conditions involving repeated transient sequestration of leukocytes, particularly in the pulmonary vasculature, may eventually be recognized as a complication of systemic complement activation. Dramatic pathologic changes observed in the lungs of animals exposed to either C3a or C5a emphasizes the potential damage that these factors may exert via cellular activation mechanisms (Huey et al., 1983). More recent evidence that the anaphylatoxins are potent immunoregulatory factors under in vitro conditions suggests a physiologic role for these humoral factors in nonspecific modulation of the immune response. It is an attractive hypothesis to suggest that once activated, complement is capable of relaying information to the cellular immune system via the anaphylatoxins. Other components of the complement system have long been known to exert regulatory influences on the immune system, and perhaps molecular description of such entities as the C3d-K fragment will serve to unravel this seemingly more complex effector system. In any case, as our understanding of both the chemical and biologic nature of factors derived from blood complement components advances, it has become apparent that a major function of complement may be to modulate the immune response. We have already demonstrated that these factors are selective both for cell type and for eliciting a variety of cellular responses. From this, one can infer that manipulation of the cellular events will eventually be possible. Hence a therapeutic value may be realized once involvement of these complement factors under in vivo conditions is better characterized.

Identification of chemoattractant activity for lymphocytes in blister fluid of patients with bullous pemphigoid: evidence for the presence of a lymphokine

Bullous pemphigoid is characterized by the dermal infiltration of lymphocytes, which precedes the striking influx of eosinophils as the lesion evolves into the bullous phase. This finding prompted a search for chemoattractant activity for lymphocytes in the blister fluid of untreated individuals with bullous pemphigoid. We found such activity in the bullous fluids of 6 consecutive patients but not in a patient with pemphigus vulgaris. This lymphocyte chemoattractant activity separates into 4 peaks upon Sephadex G-100 chromatography and the peak of 56,000 daltons was further evaluated. Upon quaternary aminoethyl Sephadex-anion exchange chromatography this peak elutes at 4-8 ms and with preparative isoelectric focusing it demonstrates an isoelectric point of 8.6-9.0. This activity was susceptible to degradation by trypsin and neuraminidase, but was stable upon heating to 56 degrees C for 30 min. Its chemoattractant activity is predominantly chemokinetic by checkerboard analysis. As defined by chromatography, stability, and functional characteristics, this activity is similar to a recently described human lymphocyte chemoattractant lymphokine. This finding suggests that products of activated lymphocytes are present in blister fluids of patients with bullous pemphigoid and may contribute to the early influx of lymphocytes in this disease.

Binding of the third component of complement (C3) to Thy-1.2 positive Con-A-induced blasts of the murine spleen: modulation of the C3 binding and cell aggregation by protease inhibitors

The binding of the third component of the complement system (C3) to Con-A-stimulated murine spleen cells (MSPC) and the role of C3 for the formation of cell aggregates was examined. C3 became bound up to 15% of the T blasts (Thy-1.2 positive cells) while only 2.5% of the non-activated T cells bound C3 when they were incubated with autologous serum. Application of purified human C3 or heat-inactivated autologous serum did not result in a detectable C3 binding. The highest percentage of C3-carrying T blasts (15% of Thy-1.2 positive cells) was observed concomitantly with maximum [³H]-thymidine incorporation when cells were harvested between 24 and 38 hours of culturing. Treatment of the Con-A-stimulated MSPC with phenylmethylsulphonylfluoride (PMSF) and soybean trypsin inhibitor (SBTI) induced a decrease of the percentage of C3-binding T blasts. However, at small concentrations the protease inhibitors (PI) effected increased C3 binding depending on the time of harvesting the cells. The PI when applied in concentrations causing an enhancement of the percentage of C3-positive T cells also increased the aggregation of Con-A-stimulated MSPC. In contrast Con-A-stimulated MSPC aggregated less when treated with autologous mouse serum containing anti-mouse C3. These observations suggest that the cell contact among Con-A-stimulated MSPC in the presence of serum is at least in part mediated by C3 bound to T-cell blasts. Based on these and previous findings that certain concentrations of DFP enhance rosette formation of blast-transformed B cells with EAC1423b, we hypothesize that PI are involved in regulation of B- and T-blast membrane metabolism, thereby influencing C3-deposition on T-cell blasts and C3-dependent cell—cell interaction.

Induction of interleukin 1 secretion and enhancement of humoral immunity by binding of human C5a to macrophage surface C5a receptors

The mechanism by which human C5a anaphylatoxin augments the primary humoral response of murine splenocytes to antigen has been investigated. Culture supernatants were generated from splenic adherent cells or macrophage cell lines after exposure to a brief pulse of human C5a. Supernatants from the macrophage-like cell line P388D1, which bears surface receptors for C5a, enhance the PFC response to antigen, whereas those from the closely related cell line P388, which lacks surface receptors for C5a, fail to cause enhancement. Supernatants from splenic adherent cells, which also bear C5a receptors, similarly augment the SRBC response. Active supernatants, but not those devoid of activity, were shown to contain interleukin 1 (IL-1) activity by both the thymocyte mitogenesis and thymocyte costimulator assays. None of the supernatants contained IL-2 activity. These observations suggest that the recently described role of human C5a as an immunopotentiating modulator is mediated by its ability to induce production of IL-1 upon binding to specific receptors at the macrophage cell surface.

The presence of a receptor for complement on T lymphocytes. Restriction of the complement receptor to Fc-receptor-bearing T lymphocytes

Using rhodaminated guinea pig anti-ovalbumin:ovalbumin:complement complexes, a fluoresceinated monoclonal anti-Thy 1 antibody and a FACS-II equipped with dual fluorescence detection channels, we find that 25-30% of Thy 1+ splenocytes express a receptor for complement. That a receptor for complement is involved in binding the guinea-pig AgAb:C' complexes is supported by the observations that: a) guinea-pig complexes, which were not treated with a serum source of complement or which were treated with either fresh serum in the presence of EDTA or with heat-inactivated serum, do not bind to the T lymphocytes, and b) heat-aggregated human gamma globulin, which effectively inhibits binding of mouse AgAb complexes to the aFcR gamma, has no effect on the binding of guinea-pig AgAb:C' complexes to the T lymphocytes. By analyzing cell subpopulations isolated by cell sorting, it is demonstrated that the C'R-positive T lymphocyte clearly delineates a major subpopulation of aFcR gamma-positive T lymphocytes, whereas no cells are found bearing a C'R, while lacking the aFcR gamma. The implications of the presence of a C'R in immunoregulation are discussed.

Inhibition of human lymphocyte blastogenesis by C3: the role of serum in the tissue culture medium

Preparations of the third component of human complement (C3) inhibit human lymphocyte blastogenic response to mitogens and antigens when cultured in serum-free medium or in medium supplemented with 5% autologous serum (AS). In contrast, when the culture medium was supplemented with 5% foetal calf serum (FCS), C3 failed to inhibit responses to mitogen (concanavalin A) or to antigen (streptolysin O); some FCS lots allowed stimulation rather than inhibition of the lymphocyte responses. Moreover, when lymphocytes were cultured in serum containing equal amounts of FCS and AS, no inhibition was seen. Our findings may explain previous studies which suggest that C3 enhances or has no effect on lymphocyte responses.

Activation of human monocytes by both human beta 1H and C3b

We tested whether highly purified human β1H and C3b, two proteins of the alternative pathway of complement activation, could exert an influence on the activity of human monocytes (Mφ). The activation process of Mφ was assessed by measurements of the respiratory burst in terms of nitro blue tetrazolium (NBT) reduction and by chemiluminescence (CL) tests. In NBT reduction experiments, we found a tendency for β1H to increase NBT reduction, while C3b was found to be rather inhibitory. In CL measurements, both β1H and C3b displayed a stimulatory effect on Mφ, showing different time- and dose-dependency. For β1H, the maximum stimulation occurred after 15 min, whereas for C3b after 45 min. Zymosan particles which served as a positive control also showed the highest stimulation after 45 min. In dose—response experiments, β1H reached a plateau ranging from 30 to 80 μg/ml. In contrast, using C3b up to 170 μg/ml, no plateau was reached. Mφ-depletion and enrichment studies suggested at Mφ as being responsible for the stimulatory effects found.

The differences between NBT reduction and CL could possibly be explained by the measurement of only cell-bound reductive potentials by NBT reduction, while in CL measurements, products of the extracellular space are also assessed. Our results suggest that both human β1H and C3b are appropriate stimuli for human monocytes.

DNA synthesis-potentiating activity on mouse thymocytes of synovial fluid of rheumatoid arthritis patients

DNA synthesis-potentiating activity in synovial fluids of rheumatoid arthritis (RA) patients was studied in vitro by using phytohemagglutinin-stimulated mouse thymocytes. The activity was present only in fluids obtained during the active RA phase, and no activity was noted in fluids obtained during the inactive RA phase or in fluids of osteoarthritis deformans patients.

Anaphylatoxin-mediated regulation of the immune response. I. C3a-mediated suppression of human and murine humoral immune responses

The C3a fragment of the third component of complement was found to have immunosuppressive properties. C3a is capable of suppressing both specific and polyclonal antibody responses. In contrast, C3a had no effect on antigen- or mitogen-induced B or T cell proliferative responses. The carboxy-terminal arginine is essential for C3a to exhibit its immunosuppressive properties. The serum carboxypeptidase inhibitor 2-mercaptomethyl-5-guanodinopentanoic acid, which prevents cleavage of the terminal arginine that would produce C3ades Arg-77, allowed us to assay the effects of C3a on in vitro immune response systems where serum is required. When the terminal arginine is removed from C3a, the resulting C3ades Arg-77 molecule is nonsuppressive. Helper T lymphocytes are the target of C3a-mediated suppression of the immune response. Substitution of T cells by soluble T cell factors was found to abrogate the C3a suppressive activity.

Human membrane-bound C3 receptors. I. Serological and immunohistological demonstration of C3 receptors

The aim of the present study was to present further evidence of the specific reactivity of an anti-C3 receptor serum (AC3RS), to demonstrate membrane-bound C3 receptors by using this AC3RS in different serological an immunohistological methods, and to investigate the relationship between membrane-bound C3 receptors and alpha1-antitrypsin. The AC3RS, or F(ab')2 fragments of the IgG fraction of this antiserum, stained a percentage of various viable cell populations roughly equivalent to the number of cells that bound EAC3b and/or EAC3d; C3 receptor-negative T cells and thymocytes were not stained. On frozen sections of tonsils and kidneys it was found that the AC3RS stained area to which EAC3b adhered. After absorption with neutrophils or Ehu, the AC3RS inhibited the agglutination of EAC3d with tonsil cells, but not the agglutination of tonsil cells or neutrophils with EAC3b; this absorbed AC3RS still stained tonsil cells but not neutrophils, and in frozen tonsil sections it stained only those areas to which EAC3d adhered. The absorbed AC3RS did not stain glomeruli. Antisera to alpha1-antitrypsin failed to inhibit EAC agglutination with C3 receptor-bearing cells or to stain C3 receptor-positive cells either in suspension or in frozen sections. Absorption of th AC3RS with purified alpha1-antitrypsin did not affect its specific reactivity.

Human membrane-bound C3 receptors. II. Physiochemical properties of the C3b and C3d receptors isolated from tonsil cells by immunoprecipitation

The aim of the present study was to define the physicochemical structure of C3b and C3d receptors of lymphoid cells. C3b and C3d receptors were isolated from KBr lysates of the 20,000 g fraction of human tonsil homogenates by immunoprecipitation with an anti-C3 receptor serum (AC3RS). Sodium dodecyl sulphate (SDS) gel filtration and polyacrylamide gel electrophoresis (PAGE) of unreduced immunoprecipitates revealed a highly predominant component with an apparent molecular weight (mol. wt.) greater than 1 x 10(6) and a small component with a mol. wt. of 80,000. After reduction, the SDS-PAGE profile was made up of a constant major 38,000 mol. wt. component and a inconstant smaller 18,000 mol. wt. component. The 38,000 (and also the 18,000) component could be isolated only from C3 receptor-active lysates, and not from C3 receptor-negative lysates. Taken together, the results of this study suggest that the active C3 receptor molecule of tonsil cells is a lipoprotein complex with a mol. wt. greater than 1 x 10(6); its protein moiety consists predominantly of disulphide-bridged polypeptide chains with a mol. wt. of 38,000; C3b and C3d receptors are composed of equal-sized polypeptide chains, but the specific binding sites for C3b and C3d are located on different molecules.

Release of endogenous C3b inactivator from lymphocytes in response to triggering membrane receptors for beta 1H globulin

Human bone marrow-derived lymphocytes and cells from B lymphoblastoid lines were shown to have specific membrane receptors for beta 1H globin. Lymphocytes responded to the presence of beta 1H by releasing endogenously-synthesized C3b-inactivator. Very little spontaneous release of C3b-inactivator occurred in the absence of beta 1H. beta 1H-treated lymphocytes that either lacked complement receptor type one (CR1, the C4b-C3b receptor) or had their CR1 blocked with Fab'-anti-CR1 formed rosettes with C3b-coated sheep erythrocytes (EC3b) by adherence to complement receptor type two (CR2, the C3d-C3bi receptor). The mechanism of the beta 1H-induced EC3b rosette formation was shown to involve the release of lymphocyte C3b-inactivator that cleaved bound C3b into C3bi forming EC3bi. This lymphocytes-generated EC3bi then bound to CR2, forming rosettes. beta 1H-induced EC3b rosettes were completely inhibited by the presence of either anti-C3b-inactivator, F(ab')2-anti-CR2, Fab-anti-C3c, or Fab-anti-C3d, but were unaffected by the presence of fluid-phase concentrations of beta 1H up to 5.5 mg/ml or Fab'-anti-CR1. Analysis by sodium dodecyl sulfate polyacrylamide gel electrophoresis and fluorography demonstrated that cell-free supernates of beta 1H-treated lymphocytes cleaved 3H-labeled C3b on EC3b into C3bi. Inhibition studies with chelating agents and sodium azide suggested that the release of C3b inactivator might involve a calcium and energy-dependent transport of this enzyme across the membranes of beta 1H-triggered cells. Because plasma beta 1H and C3b-inactivator are known to have important functions in the distinction of alternative pathway-activating substances from normal tissue, it is possible that this beta 1H receptor-C3b-inactivatory releasing system in lymphocytes may have an analogous function.

Isolation and characterization of leukaemic B-lymphocytes: influence of anticoagulant on C3-receptor detection, humoral killing and capping of cell surface immunoglobulin

Guinea pig L2C neoplastic B-lymphocytes processed from leukaemic blood collected into EDTA as anticoagulant exhibited high affinity rosetting for EAC mouse indicator cells. Partial blocking of the C3-receptors was apparent with blood collected into heparin or citrate as anticoagulant. This could be minimized by keeping the temperature at 4 degrees C and avoided by ensuring a high final concentration of citrate (greater than or equal to 40 mM). Results from experiments in vitro suggested that receptor blocking may have been a consequence of complement activation by the L2C cells occurring via the alternative pathway. No injury to the cells was evident with any of the anticoagulants used, and their susceptibility to antibody-dependent complement-mediated lysis was independent of anticoagulant and unaffected by the irregular presence of membrane-bound C3. In experiments where the antibody-induced redistribution of L2C surface immunoglobulin was investigated, it was found that cells processed from blood collected into EDTA showed poor ability to cap and interiorize their surface immunoglobulin in comparison with cells processed from heparinized or citrated blood. Inhibition of capping was found to be dependent on the concentration of EDTA and could be avoided by collecting blood into a large volume of low molarity EDTA as opposed to a small volume of high molarity EDTA. Some practical and theoretical consequences of our observations are discussed.