Polyclonal activation of human B lymphocytes by Fc fragments. I. Characterization of the cellular requirements for Fc fragment-mediated polyclonal antibody secretion by human peripheral blood B lymphocytes

Characterization of novel multiantigenic vaccine candidates with pan-HLA coverage against Mycobacterium tuberculosis

The low protection by the bacillus Calmette-Guérin (BCG) vaccine and existence of drug-resistant strains require better anti-Mycobacterium tuberculosis vaccines with a broad, long-lasting, antigen-specific response. Using bioinformatics tools, we identified five 19- to 40-mer signal peptide (SP) domain vaccine candidates (VCs) derived from M. tuberculosis antigens. All VCs were predicted to have promiscuous binding to major histocompatibility complex (MHC) class I and II alleles in large geographic territories worldwide. Peripheral mononuclear cells (PBMC) from healthy naïve donors and tuberculosis patients exhibited strong proliferation that correlated positively with Th1 cytokine secretion only in healthy naïve donors. Proliferation to SP VCs was superior to that to antigen-matched control peptides with similar length and various MHC class I and II binding properties. T-cell lines induced to SP VCs from healthy naïve donors had increased CD44(high)/CD62L(+) activation/effector memory markers and gamma interferon (IFN-γ), but not interleukin-4 (IL-4), production in both CD4(+) and CD8(+) T-cell subpopulations. T-cell lines from healthy naïve donors and tuberculosis patients also manifested strong, dose-dependent, antigen-specific cytotoxicity against autologous VC-loaded or M. tuberculosis-infected macrophages. Lysis of M. tuberculosis-infected targets was accompanied by high IFN-γ secretion. Various combinations of these five VCs manifested synergic proliferation of PBMC from selected healthy naïve donors. Immunogenicity of the best three combinations, termed Mix1, Mix2, and Mix3 and consisting of 2 to 5 of the VCs, was then evaluated in mice. Each mixture manifested strong cytotoxicity against M. tuberculosis-infected macrophages, while Mix3 also manifested a VC-specific humoral immune response. Based on these results, we plan to evaluate the protection properties of these combinations as an improved tuberculosis subunit vaccine.

Signal peptides and trans-membrane regions are broadly immunogenic and have high CD8+ T cell epitope densities: Implications for vaccine development

Cell mediated immune response has a major role in controlling the elimination of infectious agents. The rational design of sub-unit peptide vaccines against intracellular pathogens or cancer requires the use of antigenic sequence/s that can induce highly potent, long lasting and antigen-specific responses in the majority of the population. A promising peptide selection strategy is the detection of multi-epitope peptide sequences with an ability to bind multiple MHC alleles. While past research sought the best epitopes based on their specific antigenicity, we ask whether specific defined domains have high epitope densities. Signal peptides and trans-membrane domains were found to have exceptionally high epitope densities. The improved MHC binding of these domains relies on their hydrophobic nature and, in signal peptides, also on their specific sequence. The high epitope density of SP was computed using in-silico methods and corroborated by the high percentage of identified SP epitope in the IEDB (immune epitope database). The enhanced immunogenicity of SP was then experimentally confirmed using a panel of nine peptides derived from Mycobacterium tuberculosis (MTb) proteins used in human PBMC proliferation assays and T cell lines functional assays. Our results show the exceptionally high antigen specific response rates and population coverage to SP sequences compared with non-SP peptide antigens derived from the same proteins. The results suggest a novel scheme for the rational design of T cell vaccines using a domain based rather than an epitope based approach.

Regulation of human B lymphocyte activation by opioid peptide hormones. Inhibition of IgG production by opioid receptor class (mu-, kappa-, and delta-) selective agonists

Opioid peptides have been reported by many laboratories to modulate in vitro and in vivo cell-mediated and humoral immune responses. However, less attention has been afforded to the class or classes of opioid receptors involved in these immunomodulatory effects. Previous studies by this laboratory indicated that beta-endorphin and methionine-enkephalin were potent inhibitors of Staphylococcus aureus, Cowen strain I (SAC)-induced IgG production by human B lymphocytes. Results obtained from the present studies indicate that, at pharmacological concentrations, mu-, delta-, and kappa-receptor-selective agonists are potent inhibitors of SAC-induced IgG-secreting cells (IgG-ISC) by human B lymphocytes. Moreover, the suppression of IgG-ISC formation was reversed by mu-, delta-, and kappa-receptor class-selective antagonists, [D'Tic]cTAP, ICI 174,864, and nor-BNI, respectively. These findings are in agreement with other studies showing that more than one class of receptors are involved in opioid peptide-mediated immunoregulation. Additional studies indicated that all three class-selective receptor agonists were found to suppress SAC-induced IL-6 production in intact PBMC cultures. As observed for suppression of IgG-ISC formation, inhibition of IL-6 production was found to be reversed by the appropriate receptor class-selective antagonist. These results support the hypothesis that one mechanism of opioid peptide-mediated inhibition of antibody production is via the down regulation of cytokine synthesis.

Polyneuropathy associated with IgA monoclonal gammopathy: a hypothesis of its pathogenesis

We describe three patients with chronic progressive polyneuropathy associated with IgA monoclonal gammopathy. Two patients had a prominent sensory neuropathy and one had a prominent motor neuropathy. Sural nerve biopsies showed axonal degeneration in all cases. In immunocytochemical studies patients' IgG immunostained axons. By Western immunoblot a band of IgG reactivity with an axonal protein of 66 kDa was found. No band of IgA and IgM were found. We suggest the possibility that the IgA monoclonal protein may act as a stimulating factor of preexisting B cell clones eliciting an immune reaction against nerve antigens.

Modulatory effect of synthetic human IgG Fc peptides on the in vitro immune response of murine spleen cells

Synthetic peptides representative of defined surface-exposed sequences within the CH-2 and CH-3 domains of human IgG1 induce IgM production by murine spleen cells, even in cultures depleted of T-lymphocytes. This stimulation was not altered by simultaneous administration of dextran sulphate in suboptimal concentration, its effect being additive to that of the peptides. Cell proliferation was augmented only at 10(-4) M doses of peptides. IL-1 production by adherent cells was also increased as a result of peptide treatment; whilst administration of exogenous IL-1, 4 h later, seemed to abrogate the effect of peptide treatment on the augmentation of IgM production. Peptide treatment failed to induce IL-2 and/or IL-4 production. The effect of IgG peptides seems to be exerted directly on B-cells at an early step of activation and to be mediated at least in part by IL-1.

C5a-mediated release of interleukin 6 by human monocytes

Recombinant human C5a (rC5a) was assessed for its ability to induce interleukin 6 (IL-6) production in human peripheral blood-derived mononuclear cell (PBMC) cultures. rC5a was observed to induce IL-6 production as measured by hybridoma growth promotion (B9.9 assay) and human B cell differentiation (SKW6.4 assay). Optimal IL-6 production was obtained after 24 hr stimulation with 0.1-0.5 micrograms/ml rC5a. In addition, natural human C5ades Arg and natural porcine C5a were able to induce a similar level of IL-6. The observed IL-6 activity appeared not to be due to endotoxin contamination since heat treatment (100 degrees C/15 min) inhibited rC5a induction of IL-6. The rC5a stimulation also induced an increase in steady-state IL-6 mRNA as determined by Northern blot analysis. Pretreatment of PBMC with leucine-methyl ester to deplete monocytes reduced the rC5a-induced IL-6 production to background levels. In addition, stimulation of purified T cell preparations with rC5a produced little IL-6 activity, suggesting that monocytes are the major source of IL-6 in this system. These results suggest that the inflammatory and immunoregulatory activities of C5a may in part be due to the stimulation of IL-6 release, a cytokine which possesses potent pleiotropic functions.

Suppression of human B lymphocyte activation by beta-endorphin

The effects of beta-endorphin (beta-E) and contained peptides were investigated for their ability to regulate Staphylococcus aureus (SAC)-induced immunoglobulin secretion by human B lymphocytes. Co-culture of beta-E with SAC-stimulated peripheral blood-derived mononuclear cells, under serum-containing or serum-free conditions, resulted in a dose-dependent inhibition of immunoglobulin-secreting cell (ISC) formation. When the same cultures were assessed for class-specific Ig formation it was found that IgG-ISC were suppressed to a greater extent that IgA-ISC or IgM-ISC. In contrast to these results, beta-E was found to be unable to suppress SAC-induced lymphocyte proliferation. To map the suppressive activity associated with beta-E, truncated peptides based on the beta-E sequence were assessed for biological activity. The results indicated that peptides containing the N-terminal region of beta-E suppressed ISC formation. Moreover, methionine-enkephalin (beta-E 61-65) was found to be effective in suppressing ISC formation. beta-E-mediated suppression of IgG-specific ISC formation appears to involve classical receptor-ligand interaction as evidenced by the ability of naloxone to block suppression of ISC formation.

Fc fragment from human IgG induces PGE2 secretion. II. Negative regulation in B cell differentiation

In humans, in vitro, Fc fragment of IgG at a low concentration induces plasma cell generation. However, Fc fragment at a high concentration induces PGE2 release of monocyte activation capable of inhibiting this differentiation. The levels of PGE2 in the supernatant culture from mononuclear cells from normal donors were examined as a function of culture duration and concentration of Fc, Fab fragments and IgG. Plasma cells containing intracytoplasmic Ig were demonstrated by immunofluorescence with a polyvalent antiserum to human immunoglobulin(s). PGE2 levels, from mononuclear cell cultures, were analyzed by the RIA test. The results indicated that the Fc fragments are able to induce PGE2 secretion. The maximal release of PGE2 occurs after 24 hr of culture; this level is proportionate to the quantity of Fc fragments introduced. The addition of indomethacin in the cell culture stimulated by a high concentration of Fc fragments reestablishes the percentage of plasma cells. These results suggest the regulatory role of Fc fragment by PGE2 secretion in B cell differentiation.

Human B cell differentiation by Fc fragment. III. Effect of IL-1 and IL-2 on differentiation of human B lymphocytes induced by Fc fragments of human IgG

The human Fc fragment of IgG, when added to blood mononuclear cells in vitro, induces B cell differentiation after 6 days of culture. This activity requires the presence of T cells and monocytes. This work explores the roles of interleukin 1 (IL-1) and interleukin 2 (IL-2) in B cell differentiation induced by Fc fragments. Peripheral blood mononuclear cells (PBMC) from normal donors were examined for plasma cell differentiation following stimulation with Fc fragment (15 and 30 micrograms/ml) with or without IL-1 (6 U/ml) or IL-2 (2 U/ml). Results indicate that both IL-1 and IL-2 accelerated B cell differentiation by the Fc fragment to 3 days of culture, compared to 6 days required with the Fc fragment alone. The time required for differentiation was not further shortened when both IL-1 and IL-2 were present in culture; both IL-1 and IL-2 were able to partially induce B differentiation alone at 6 days of culture. The importance of IL-2 in B cell differentiation was further supported by the finding that antibodies specific for the IL-2 receptor blocked B cell differentiation induced by Fc fragments, with or without additional IL-1 or IL-2. The depletion of monocytes also blocked B cell differentiation and the requirement for monocytes could not be replaced by exogenous IL-1; however, Fc fragments were shown to induce monocytes to secrete IL-1 beta after 24 hr in culture. These results suggest that accelerated differentiation of B cells into plasma cells requires a double signal provided by Fc fragments and IL-1 or IL-2. Monocytes are necessary for Fc fragment-induced differentiation and cannot be replaced by either IL-1 or IL-2.

Induction of human B cell differentiation by Fc region activators. I. Identification of an active tetrapeptide

Addition of pFc' fragments, composed of residues 334 to 446 in the Fc region of human IgG1, to cultures of human peripheral blood mononuclear cells resulted in the induction of Ig-secreting cells (ISC). Intact IgG1 and F(ab')2 fragments were inactive. The synthetic peptide p23, representing residues 335 to 357, retained the ISC-inducing property of pFc' fragments. The ISC response to p23 exhibited the isotype pattern IgMSC greater than IgGSC greater than or equal to IgASC. Results from cell depletion experiments revealed that the B cell response to p23 was T cell dependent but relatively monocyte independent. Cell proliferation was not increased in p23-stimulated PBMC cultures. Overlapping synthetic peptides based on the sequence of p23 were used to localize the active site in this molecule. These studies revealed that LPPSR (residues 351 to 355) was the sequence responsible for the ISC-inducing property of p23; however, expression of activity by this pentapeptide sequence could be dampened by N-flanking sequences. Finally, residue-deleted analogs of LPPSR were used to determine that LPPS was the minimum sequence retaining activity. Collectively, these data suggest that the fragmentation of IgG results in the expression of a tetrapeptide sequence with lymphocyte-stimulating properties.

Immunomodulatory effect of synthetic peptides corresponding to sequences within the CH2 and CH3 domain of human IgG1

The Fc region of IgG is known to be the source of small peptides possessing immunomodulatory function. Results are summarized showing the effect of synthetic peptides composed of surface exposed residues of C gamma 2 or C gamma 3 domains on different steps of human B lymphocyte activation cycle. Both the CH2 (289Thr-301Arg) and CH3 (407Tyr-416Arg) peptides as well as the whole Fc fragment enhanced the IgM synthesis of PWM or PMA + CaI activated lymphocytes. This effect was exerted at the early phase of B cell activation. The incubation of separated resting B cells with Fc fragments or CH2 peptides resulted in increase of cell volume and in expression of HLA-DR antigen. On the other hand, LIF production was induced both by CH2 and CH3 peptides. It was also shown that Fc peptides induce IL-1 release from monocytes. The results suggest that the CH2 and CH3 domain peptides exert their effect partly directly, by activating resting B cells, rendering the cells more susceptible to other stimuli; and moreover, by enhancing the humoral response by triggering the release of IL-1.

Human B-cell differentiation by Fc fragment of IgG. I. Fc fragment from human IgG induces plasma cell generation but cannot induce lymphocyte proliferation

Circulating mononuclear cells (MNC) from normal donors were examined for lymphocyte proliferation and plasma cell differentiation following stimulation by Fc and Fab fragments or by intact IgG. Lymphocyte differentiation and DNA synthesis were examined as a function of culture duration and concentration of Fc, Fab fragments, and IgG. Plasma cells containing intracytoplasmic Ig were demonstrated by immunofluorescence with a polyvalent antiserum to human immunoglobulin and with specific antisera (anti-mu, -gamma, -alpha, -delta, -kappa, and -lambda chains). DNA synthesis of mononuclear cells cultures was analyzed by measuring [3H]thymidine incorporation. The results indicated that only the Fc fragments are able to induce the differentiation of B cells. The polyclonal plasma cell response to Fc fragments was dose dependent, peaked on the sixth day of culture, and was isotypically diverse (IgM greater than IgA greater than IgG). This activity requires the presence of T helper cells and monocytes. In contrast, the Fc fragments were unable to induce a proliferative response.

The evasion of the immune response and immunological unresponsiveness: parasitic helminth infections

A selective review is given of the mechanisms associated with the evasion of the immune response by parasitic helminths and immunological unresponsiveness as it applies to helminth infections. Immunosuppression caused by parasites leading to reduced responsiveness of lymphocytes to mitogens is discussed, and mechanisms that inhibit effector mechanisms at the parasite surface and polyclonal activation of lymphocyte populations are dealt with. Physiological immunosuppression associated with parturition and lactation and the immunological unresponsiveness of young ruminants are dealt with in detail.

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.

Antagonistic regulatory properties of the Fc region of immunoglobulin

Coculture of human peripheral blood mononuclear cells with Fc fragments of human IgG, or the synthetic Fc region-derived peptide, p23, results in the release of oxidative products of arachidonic acid. Prostaglandin E was the major arachidonic acid metabolite found in the culture supernatants. Induction of polyclonal antibody production by Fc fragments and p23 is influenced by the concomitant production of prostaglandin E in culture. Addition of prostaglandin synthetase inhibitors, indomethacin and aspirin, to human peripheral blood mononuclear cell cultures resulted in a significant increase in the amount of polyclonal antibody produced. Moreover, addition of exogenous prostaglandin E to these cultures abrogated the ability of indomethacin to enhance Fc fragment-induced polyclonal antibody production. These results suggest that Fc fragments possess bifunctional immunoregulatory properties.

Modulation of the immune response by immunoglobulin for intravenous use. II. Inhibitory effects of sera from treated patients

Sera were collected from patients with common varied immunodeficiency (CVI) prior to and following intravenous gamma-globulin (IVGG) infusion. Cultures of pokeweed mitogen (PWM)-stimulated peripheral blood mononuclear cells from normal donors in medium containing post-IVGG infusion sera generated significantly fewer plaque-forming cells (PFC) than those cultures in medium containing the corresponding pre-IVGG infusion sera. However, preinfusion CVI sera were found to be similar to normal sera in their capacities to support PWM-induced PFC generation, despite the disparity in Ig levels between the two groups of sera. Furthermore, serum collected from a CVI patient 24 hr or more after IVGG infusion no longer possessed the same inhibitory capacity as serum collected 10 min after IVGG infusion despite elevated IgG levels compared to baseline. These studies suggest that IVGG infusion may induce an immunosuppressive effect which is transient in nature, raising the possibility of in vivo counterbalancing homeostatic mechanisms responding to this immune perturbation.

Lymphocyte activation by the Fc region of immunoglobulins

The Fc region of Ig is required for numerous biological effector functions which include: opsonization, anaphylaxis, C fixation, catabolism of the Ig molecule, FcR binding, and immune regulation. To this latter point, the cellular and subcellular events involved in immune regulation by IC and Fc fragments of Ig have been the focus of numerous investigations. Characterization of cyanogen bromide cleavage fragments from a human IgG1 myeloma protein indicates that one biologically-active site is found in residues 335-357 of the CH3 domain of the molecule. Synthesis of the biologically-active region resulted in a peptide, termed p23, which stimulates mouse and human B cells to secrete polyclonal Ig and activates AA metabolic pathways. In contrast to these findings, p23 is unable to induce B cell proliferation or IL-1 secretion from macrophages. Analysis of data obtained with overlapping peptides, based on p23, suggests that the minimal active sequence needed for B cell differentiation is leu-pro-pro-ser-arg (residues 351-355). In contrast, only p23 or p23 minus the carboxyterminal glu356 and glu357 were able to induce PGE release. Release of biologically-active peptides derived from the Fc region of Ig into the cellular microenvironment may form the nucleus of a nonspecific in vivo immunoregulatory network. The specificity of peptide regulatory activities could reside in their effectiveness at high concentrations in the cellular microenvironment. The interaction of Fc region peptides with receptors on B cells, T cells, and macrophages/monocytes could result in a dynamic control of immune reactivity.

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.

Polymorphism of Fc receptor on murine B cells is Igh-linked

Analysis of mouse IgG binding to Fc receptors on mouse B cells indicates that the IgG1, IgG2a, and IgGb subclasses bind to the same receptor. No differences in affinity were detected among subclass or between mouse strains. This same receptor bound rat IgG with an affinity that differed between mouse strains. This polymorphism in affinity for rat IgG maps to chromosome 12 distal to the Igh locus.

Rosette formation between T and autologous B lymphocytes. I. Characterization of a T cell subpopulation

The ability of some T cells to form rosettes with autologous B lymphocytes (TrB cells) appears to be a marker of a subpopulation of T cells, a majority of which have high avidity receptors for sheep red blood cells. TrB cells have a higher proportion of suppressor cell surface markers (OKT-8+ and receptor for the Fc fraction of IgG), as well as higher suppressor activity than other T cell populations. TrB cells also help in B lymphocyte transformation under the stimulation of a T-dependent B mitogen. The TrB cells seem to express the Fc gamma receptor after ecotatic association with B cells, since T gamma cells previously isolated from total T cells form rosettes with B cells in the same proportion in which total T cells do. Studies on TrB cells subpopulation may explain some of the defects in functional cell-cell interactions.

Binding and processing of immunostimulatory Fc gamma 1 fragments by the murine macrophage cell line P388D1

Previous data from this laboratory indicated that human Fc gamma fragments induce murine B cells to proliferate and that the induction is macrophage-dependent. To further investigate the role of macrophages in this phenomenon, biologically active Fc gamma fragments from a human IgG1 myeloma protein and the murine macrophage-like cell line P388D1 were utilized. Fc gamma 1 fragments bound specifically and to a single class of receptor on P388D1 cells with a Ka value of 4 X 10(6) M-1 and to approximately 2.4 X 10(5) binding sites/cell. The binding was not effectively inhibited by two immunostimulatory Fc gamma 1 subfragments that were macrophage independent, i.e., pFc' fragments approximating the C gamma 3 domain of IgG1 and synthetic peptides representing residues 335-357 in IgG1. P388D1 cells were able to process Fc gamma 1 fragments but not intact IgG1 into subfragments that were able to induce lymphocyte proliferation in the absence of macrophages. The processing was rapid and resulted in active subfragments of several size classes. These findings not only further document the molecular and cellular events in these systems but underscore the usefulness of the P388D1 cell line in future studies on Fc fragment-induced lymphocyte regulation.

IgE Fc receptor positive T and B lymphocytes in patients with the hyper IgE syndrome

The percentages of peripheral blood lymphocytes (PBL), bearing Fc receptors for IgE (Fc epsilon R) and IgG (Fc gamma R) were determined in four patients with the hyper IgE syndrome by a rosette assay employing IgE and IgG coated fixed ox erythrocytes. The patients had 8 +/- 3% Fc epsilon R+ and 13 +/- 8% Fc gamma R+ PBL, compared to 1.2 +/- 1% Fc epsilon R+ and 17 +/- 4% Fc gamma R+ PBL for control donors. T cells were isolated by rosetting with neuraminidase treated sheep erythrocytes (EN). Indirect immunofluorescence with Lyt 3 monoclonal antibody (MoAb) to the sheep erythrocyte receptor, followed by rosetting for Fc epsilon R and Fc gamma R showed that the patients' T cells contained less than 0.1% Fc epsilon R+ and 1.4 +/- 0.2% Fc gamma R+ cells; T cells from the control subjects contained less than 0.1% Fc epsilon R+ and 11 +/- 4% Fc gamma R+ cells. The non-T (EN rosette depleted) cells of the patients included 56 +/- 18% sIgM+/sIgD+, 45 +/- 9% Fc epsilon R+ and 35 +/- 27% Fc gamma R+ cells. Indirect immunofluorescence with MoAb to IgM, IgD, and NK cells (antibody B73.1) followed by rosetting for Fc epsilon R and Fc gamma R, indicated that 92 +/- 2% of the Fc epsilon R+ cells and 9 +/- 7% of the Fc gamma R+ cells were B cells (mu+/delta+), while 3 +/- 4% of the Fc epsilon R+ and 30 +/- 23% of the Fc gamma R+ cells were NK cells (B73.1+). Thus, most of the Fc epsilon R+ non-T cells were B cells, and only a small fraction appeared to be NK cells. On the other hand, Fc gamma R+ B cells were outnumbered by Fc gamma R+ NK cells (B73.1+) by three to one. The data indicate that patients with the hyper IgE syndrome have increased numbers of Fc gamma R+ PBL, most of them being B cells, whereas their T cells contain less than 0.1% Fc epsilon R+ cells.

Potentiation of the rat delayed-type hypersensitivity reaction by the Fc portion of human IgG1

Fc fragments derived from a human IgG1 myeloma protein potentiate the rat delayed-type hypersensitivity (DTH) reaction to antigen challenge. Lewis rats immunized with heat-killed tubercle bacilli give augmented DTH reactions to the purified protein derivative of tuberculin when Fc fragments are included in the challenge dose. Similar potentiation of DTH by pFc' fragments indicates that the active site is located in the CH3 domain of IgG1. Histologic evaluation of the augmented reaction sites revealed predominantly mononuclear cell infiltrates characteristic of DTH reactions. Skin tests of tubercle bacilli-sensitized rats with an unrelated antigen and/or Fc fragments fail to elicit significant reactions. Augmentation of the DTH reaction to purified protein derivative is restricted to the Fc or pFc' region fragments since intact monomeric IgG1, Fab fragments, and bovine serum albumin were all shown not to be active potentiators. The DTH reaction of ovalbumin-sensitized rats was similarly augmented when Fc fragments were included with a challenge dose of ovalbumin, thus supporting the general nature of the phenomenon. These results support the concept of Ig molecules as multifunctional proteins that can not only serve effector functions but also participate in the regulation of immune responses.

Fc receptor--more answers, more questions

Fc receptors, belonging to the most important surface structures of a number of cells participating in the immune processes, have been intensely studied during the past decade. The present review summarizes the contemporary knowledge of the specificity and heterogeneity of Fc receptors and of factors influencing their expression, and includes some views on their function. In addition, it mentions their relationship to other cell surface structures, expression of Fc receptors during ontogeny of the organism and in certain diseases. Finally, data concerning the isolation and biochemical characterization of the Fc receptor molecule are presented.

Modulation of pokeweed mitogen-induced human B-cell differentiation by aggregated IgG

The modulatory effect of human heat-aggregated IgG on human B-cell differentiation induced by pokeweed mitogen was investigated with three experimental protocols. Pulse exposure to aggregated IgG, followed by extensive washings before culture, of peripheral blood mononuclear cell suspensions rigorously depleted of platelets and containing less than 4% monocytes resulted in a selective decrease of the numbers of IgG-containing cells and IgG-secreting cells, whereas a simultaneous decrease of the numbers of cells producing IgG and, to a lesser extent, of those producing IgM or IgA was observed when the pulsed suspensions contained platelets and more than 4% monocytes. This non-isotype-specific suppression was shown to be more pronounced when aggregated IgG and platelets were present in the cell suspensions throughout the cultures. The results suggest that two distinct suppressor pathways can be triggered by aggregated IgG. The first one is restricted to cells producing the matching isotype, in the absence of platelets, with few monocytes in the cell suspensions. The second one leads to a nonspecific suppression of the three major Ig classes. It requires the presence of platelets and/or a high percentage of monocytes and, although it remains to be demonstrated, is probably mediated by prostaglandin E2.

Non-specific potentiation of T- and B-lymphocyte proliferation at the early stage of infection by Schistosoma mansoni: role of factors secreted by the larvae

The response of rat lymphocytes to schistosomula released products (SRP) was examined. SRP non-specifically activated lymphocytes by potentiating their proliferative response to PHA, Con A or LPS. The parasite factor involved was dialysable and heat stable. The addition of SRP to cultures containing nylon-wool non-adherent lymph node cells resulted in a significant enhancement of cell proliferation. The effect of SRP on athymic nude (Nu/Nu) and litter mate (Nu/+) control rat cells indicated an effect on the proliferation of both B and T lymphocytes. SRP acted in a dose-dependent manner and its action was observed as early as the beginning of cell division. This corresponds to the in vivo situation, since at the early stage of infection increased proliferative responses of the lymph node cells to mitogens were observed. The adjuvant effect of SRP could partly explain the regulation of the cellular immune response observed during S. mansoni infection by the parasite itself and could represent one of the mechanisms involved in immunity to reinfection that is under the control of the parasite.

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.

The pathogenesis of arthritis in Lyme disease: humoral immune responses and the role of intra-articular immune complexes

We studied 78 patients with Lyme disease to determine how immune complexes and autoantibodies are related to the development of chronic Lyme arthritis. Circulating C1q binding material was found in nearly all patients at onset of erythema chronicum migrans, the skin lesion that marks the onset of infection with the causative spirochete. In patients with only subsequent arthritis this material tended to localize to joints where it gradually increased in concentrations with greater duration of joint inflammation. In joints, its concentration correlated positively with the number of synovial fluid polymorphonuclear leukocytes. Despite the prolonged presence of putative immune complexes, rheumatoid factors could not be demonstrated. These observations suggest that phlogistic immune complexes based on spirochete antigens form locally within joints during chronic Lyme arthritis.

Circulating immunoglobulin-secreting cells in rheumatoid arthritis

The level of circulating cells secreting IgG, IgM, and IgA (IgSC) provides insight into the degree of in vivo polyclonal B-cell activation (PBA). Patients with rheumatoid arthritis (RA) exhibit abnormalities in humoral immune responses suggestive of augmented in vivo polyclonal B-cell activation. Therefore, a protein A reverse hemolytic plaque assay was used to measure the level of circulating IgSC in 32 RA patients. The mean level of circulating IgSC in RA patients was 3602 +/- 747 (SEM) compared to a mean of 1407 +/- 443 in patients with other types of arthritis and 1253 +/- 216 (P less than 0.02) in healthy volunteers. Levels found in RA patients did not appear to reflect disease activity or concomitant corticosteroid therapy. However, a subset of RA patients receiving gold therapy had levels of IgSC (1381 +/- 501) similar to those seen in healthy volunteers (P greater than 0.5). These data are consistent with augmented in vivo polyclonal B-cell activation in RA. In addition they suggest that gold affects mechanisms controlling in vivo B-cell activation.

Potentiation of specific human in vitro immune responses by the Fc portion of human immunoglobulin

Fc fragments derived from a human IgG1 myeloma protein were found to be a potent adjuvant for in vitro human immune responses. The addition of Fc to cultures of human PBL along with SRBC resulted in a pronounced enhancement of the primary in vitro anti-SRBC response. In addition to potentiating the humoral immune response, Fc was also found to augment the tetanus toxoid-induced T cell proliferative response. Augmentation of the immune response is mediated by Fc and not the result of an artifact due to the addition of extraneous protein to culture because neither intact IgG1 nor Fab fragments derived from this myeloma protein possessed any adjuvant properties. The temporal relationship of the administration of antigen and Fc to culture is critical for the potentiation of the immune response. The maximal Fc adjuvant effect was observed when Fc was added with antigen at the beginning of culture.

Lymphocyte phenotype and function in pseudolymphoma associated with Sjögren's syndrome

Lymph node (LNL) and salivary gland lymphocytes (SGL) from three patients with pseudolymphoma and primary Sjögren's syndrome (1(0)SS) were characterized with monoclonal antibodies to demonstrate (a) a predominance of T cells (greater than 80%) reactive with anti-T cell antibodies OKT4 (greater than 70%) and OKT8 (less than 20%); (b) a high prevalence of activation antigens (greater than 50% of cells reactive with antibody OKT10 and anti-Ia antibody); (c) polyclonal B cells (8-15% of all cells expressing kappa or lambda); and (d) a specific B cell subset defined by reactivity with antibody B532 that was not present in their peripheral blood. In vitro functional studies showed that both SGL and LNL provided T helper activity for immunoglobulin synthesis and that this activity could be abolished by treatment with antibody OKT4 plus complement. The SGL and LNL exhibited little natural killer, antibody-dependent cellular cytotoxicity, or cytotoxic T cell activity. Normal karyotype was observed in SGL, LNL, and peripheral blood lymphocytes (PBL) from these patients. These findings indicate that pseudolymphoma in 1(0)SS results from the infiltration of salivary glands and extraglandular tissues by nonneoplastic T helper cells. Monoclonal antibodies provide an important tool to distinguish pseudolymphoma from non-Hodgkins (B cell) lymphomas that have a markedly elevated incidence in 1(0)SS patients. Our finding of T helper cells in pseudolymphoma tissues supports the hypothesis that chronic stimulation of B cells by helper T cells leads to eventual escape of a malignant B cell clone.

Monoclonal antibodies against HLA-DR antigens replace T helper cells in activation of B lymphocytes

In the presence but not in the absence of pokeweed mitogen (PWM), monoclonal antibodies against HLA-DR antigens 147 and 164 helped highly purified B lymphocytes to proliferate and mature to Ig-secreting cells. In contrast, neither anti-DR antibody 231 nor the UCHT1 monoclonal anti-human T cell antibody (both of the same isotype as the 147 and 164 anti-DR antibodies) exhibited any helper activity on B cells. B cells pulsed with PWM and subsequently cultured in the presence of anti-DR antibody 147 or 164 proliferated and secreted Ig, whereas B cells that first were pulsed with antibody 147 or 164 and then incubated with PWM did not. PWM alone did not induce any of these responses on purified B cells. Also, antibodies 147 and 164 significantly increased the number of Ig-secreting cells obtained from the WT51 Epstein-Barr virus-transformed B-cell line. Anti-DR antibody 231 inhibited the helper activity on WT51 cells mediated by anti-DR antibody 164. Finally, anti-DR antibodies 147 and 164 assisted B cells from the spleen of athymic nu/nu mice (which bear I-E-encoded products) to produce IgM antibodies against sheep erythrocytes. However, these antibodies had no effect on mouse B cells which do not express on their surface I-E-encoded Ia antigens. Taken collectively, these findings suggest that the structures detected by anti-DR antibodies 147 and 164 on B lymphocytes function as acceptors/transducers of T-cell-derived helper signals.

Synthetic Fc peptide-mediated regulation of the immune response. I. Characterization of the immunomodulating properties of a synthetic 23-amino acid peptide derived from the sequence of the CH3 domain of human IgG1

A synthetic 23-amino acid peptide derived from the CH3 domain of human IgG1 was found to be a potent adjuvant as well as a polyclonal activator. The Fc peptide was found to enhance human and murine humoral, and T cell-mediated immune responses. Moreover, in vivo administration of Fc peptide enhanced murine natural killer cell activity. The synthetic Fc peptide was found to be more potent, on a molar basis, than native Fc fragments in inducing polyclonal antibody production and potentiating immune responses.

Fc gamma of IgG: a specific agent of destabilization of lipid bilayers containing oleic acid

gamma-Immunoglobulins induce the fusion of oleic acid-containing liposomes into tubular structures. An F(ab')2 preparation does not exert the same influence unless it is several orders of magnitude more concentrated. The same is true for several proteins with an isoelectric point higher or lower than the IgG isoelectric point. The Fc of IgG seems thus to exert a specific destabilizing and fusogenic action on artificial lipid membranes. An hypothesis is presented concerning the mode of action of Fc gamma on lymphocyte membrane which is based on the facts mentioned above and on the existence of a phospholipasic activity of Fc gamma membrane receptor.

Role of Fc receptors in lymphocyte activation: deficiency in T- and B-lymphocytes from aged animals

Fc fragments derived from human immunoglobulin possess the ability to induce B-cell proliferation, polyclonal antibody responses, and augment cell-mediated and T-dependent humoral responses. However, aged animals display much lower responses to Fc fragment stimulation. Proliferation and polyclonal antibody synthesis are reduced two-five-fold in aged animals compared to the young-adult responses. Furthermore, Fc fragments are unable to potentiate plaque-forming cell (PFC) development in aged animals. Aged B-lymphocytes are deficient in responding to Fc fragments, as their admixture with young-adult T-cells does not restore polyclonal antibody formation. T-cells from aged animals are also ineffective in promoting the polyclonal response when mixed with young-adult B-cells. The T-cell lesion has been further defined as a deficiency in production of an Fc fragment induced T-cell-replacing factor [(Fc)TRF]. The inability of Fc fragments to potentiate anti-SRBC responses in aged animals is also due to a T-cell defect which can be corrected by supplementation with interleukin-2 (IL-2).

Isolation and identification of a biologically active peptide derived from the CH3 domain of human IgG1

A 24-amino acid residue peptide has been isolated from the Fc region of a human IgG1 myeloma protein. The peptide has associated with it the same ability to induce murine B cells to polyclonally secrete antibody as does the intact Fc fragment. Amino acid composition of the peptide indicates that on a mole/mole basis the isolated peptide is identical to that published for residues 335-358 in the Eu IgG1 sequence. This peptide corresponds roughly to the first 24 amino acids of the CH3 domain. It is believed that the immunoregulatory properties that have been ascribed to the Fc fragment are associated with this peptide.

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.