Fc-signalling in the modulation of immune responses by passive antibody

Passive antibody can both suppress and augment immune responses. Until recently, there was virtual unanimity on the importance of the interaction of the Fc portion of modulating antibody with Fc-receptors (Fc-signalling), especially in experiments involving the suppression by antibody. Experiments reported in the last few years, that do not demonstrate the range of Fc-portion/Fc-receptor influences on the suppression of immune responses by passive antibody, have introduced new uncertainty into this field. The purpose of this paper is to review how the initial controversy on the influence of Fc-signalling in inhibition by passive antibody was resolved. Old and new approaches are suggested that may help in resolving the current uncertainty engendered by recent experimental results that were interpreted to mean that passive suppressive antibody does not utilize the inhibitory FcgammaRIIB receptor. An understanding of the factors that influence negative Fc-signalling is needed in order to optimize clinical therapies whose action depends on the suppressive property of antibody.

Immunoreceptor tyrosine-based inhibitory motifs on activating molecules

Immunoreceptor tyrosine-based inhibitory motifs (ITIMs) have the restricted consensus sequence V/I/xYxxL/V, but may be more broadly defined by the sequence V/I/L/SxYxxL/V/I/S. If one includes the ITIM of CTLA-4, then the sequence becomes psixYxxpsi, where psi represents amino acids with nonpolar side chains. Aside from their presence in various inhibitory molecules, ITIMs are also found on many activating receptors and pathways. ITIMs with the restricted consensus sequence occur on IL-4Ralpha, IL-3Rbeta type II, gp130 cytokineR, OB-R (leptinR), LIF-Rbeta TNF-RI, G-CSF-R, PDGF-R, Blk, Ctk/Ntk, Lsk, Zap-70, PKB/RACalpha, PKC-alpha, PKC-beta, PKC-gamma, PKC-delta, PKC-zeta, PKC-epsilon, PKC-eta, PKC-phi, PKC-mu, calmodulin-dependent kinase IIdelta, SLP-76-associated protein, FYN-binding protein, Shc binding protein, RasGRF2, CDC25 homologue, Jak2, Jak3, PLCbeta1, and PLCbeta3. If ITIMs are defined by a broader consensus sequence, the list of ITIMs on activating molecules becomes even larger. In some instances, these ITIMs have been shown to associate with inhibitory phosphatases. Whether these ITIMs on activating receptors/pathways are necessary and sufficient for negative control of activating events and for immunologic tolerance is not yet known. In some instances, ITIMs on coinhibitory receptors are also required for appropriate negative regulation. By studying events leading to negative control during activation and to immunologic tolerance, it should be possible to discern the balance between antigen receptor-based negative events and coinhibition.

Why so many coinhibitory receptors?

Receptors that display negative signalling functions on lymphocytes and other cells of the reticuloendothelial system now number about 30. These negative receptors are transmembrane glycoproteins activated by phosphorylation of a tyrosine residue in immunoreceptor tyrosine-based inhibitory motifs that bind various phosphatases to induce dominant negative signals. Since these receptors are armed by the action of activating receptors and inhibit signalling by activating receptors, we have termed them coinhibitory receptors and the negative outcome is coinhibition. Coinhibitory receptors and some inhibitory mediators include FcgammaRIIB, CTLA-4, CD5, CD22, p58/70/140 KIR, gp49B1/gp91, PIRB1-5, LAIR-1, NKB1, Ly49 A/C/E/F/G, NKG2-A/B APC-R, CD66, CD72, PD-1, SHPS-1, SIRP-alpha1, ILT1-5, MIR7, 10, hMIR(HM18), hMIR(HM9), LIR1-3,5,8, Fas (CD95), TGFbeta-R, TNF-R1, IFNgamma-R (alpha and beta chains), mast cell function Ag, H2-M, HLA-DM, CD1, CD1-d, CD46, c-cbl, Pyk2/FADK2, P130 Ca rel prot, PGDF-R, LIF, LIF-R, CIS, SOCS13 and 5, and others are being defined regularly. This long list suggests that coinhibitors are needed not only for self-nonself discrimination, but also for control of ongoing responses to foreign antigens so that infectious agents are ideally dealt with by an appropriate level of immune responses to nonself and an appropriate amount of immunopathology and sickness behaviour.

FcR-mediated inhibition of cell activation and other forms of coinhibition

The tripartite inactivation model proposed that coaggregation of the B cell antigen receptor (BCR) with the Fc receptor (FcR) by antigen and specific IgG antibody complexes explained the Fc-dependent inhibition of immune responses by antibody. This model has since been substantiated by many observations and its impact on studies of immune regulation has been threefold: (1) IgG antibody, via Fc gamma RIIB, mediates inhibition of cell activation in many cell types, demonstrating the general importance of this mechanism in immune regulation; (2) Fc gamma RIIB was the first receptor described that regulates immune responses by coinhibition, that is, regulation as a result of interaction between activating receptors (BCR, TCR, Fc epsilon RI, Fc gamma RIII, Fc gamma RIIA) and inhibitory receptors (Fc gamma RIIB, CTLA4, CD5, CD22, p58/70/140 KIR, gp49B1/gp91, Ly49A/C/E/F/G, NKG2-A/B, APCR, Fas (CD95), TGF beta-R, TNF-R, IFN gamma-R, and others). The list of coinhibitors is expanding, just as the list of costimulators has grown. Tolerance through multiple coinhibitors implies that Signal 1 alone is not tolerogenic; and (3) Studies of Fc gamma RIIB coinhibitory mechanisms have pointed the way to potential general inhibitory signaling pathways used by many receptors, involving the competing effects of various kinases and phosphatases, and other competitive events. Investigations of Fc gamma RIIB physiologic function and of other coinhibitory receptors, together with recent biochemical analyses, give an initial understanding of the biology of these inhibitory receptory receptors. Paradoxes within and between theoretical constructs, functional observations, and mechanistic studies point to critical questions for future study.

Effect of major histocompatibility complex expression on murine intestinal graft survival

BACKGROUND

Clinical intestinal transplantation has been plagued by frequent and severe graft rejection. It has been proposed that the major histocompatibility complex (MHC) antigens might play a critical role in this process owing to their extensive expression on enterocytes and mucosa-associated immune cells.

METHODS

The present study examined the role of MHC antigens in intestinal graft rejection using MHC class I-deficient and MHC class II-deficient donors.

RESULTS

Grafts with normal MHC expression were rejected by 9 days, whereas survival was prolonged to 14 days in the MHC class II-deficient grafts (P=NS) and to 20 days in the MHC I-deficient grafts (P<0.002). In all groups, early rejection was characterized by (1) increased crypt cell apoptosis, as detected by the terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling (TUNEL) technique of in situ labeling; and (2) the increased expression of perforin and a CD8 phenotype in the graft-infiltrating cells.

CONCLUSIONS

These data suggest that MHC antigens, CD8-positive T cells, and perforin-expressing cells contribute to intestinal graft rejection. Apoptosis of the progenitor epithelial crypt cells during early intestinal rejection may impair the gut's ability to regenerate and repair mucosal damage.

Hypogammaglobulinaemia occurs in Fas-deficient MRL-lpr mice following deletion of MHC class II molecules

Fas (CD95)-mediated apoptosis in B and T cells is deficient in both human autoimmune lymphoproliferative syndrome and in MRL-lpr mice, a model for systemic lupus erythematosis (SLE). Autoimmune disease in these mice is associated with polyclonal B cell activation, increased serum immunoglobulin and autoantibodies. In non-autoimmune mice MHC class II is not required for normal serum immunoglobulin expression, and previously we have shown using MHC class II-deficient MRL-lpr mice (MRL-lpr Ab-/-) that generation of specific antibodies to DNA requires MHC class II-directed T cell help. In contrast, in the present study we demonstrate that MRL-lpr Ab-/- mice also have a profound reduction of total serum immunoglobulin levels, suggesting abnormal polyclonal regulation of B cells by MHC class II-directed T cells occurs in the autoimmune MRL-lpr strain. This abrogation of immunoglobulin production does not occur in MHC class II-deficient non-obese diabetic (NOD) mice, nor in MHC class I-deficient NOD or MRL-lpr mice. Reduced immunoglobulin levels in MRL-lpr Ab-/- mice were not due to a lack of B cells or to an increased loss of circulating immunoglobulin, but were associated with reduced numbers of surface IgG-positive B cells. These results define a general abnormal regulation of B cells in MRL-lpr mice through a process requiring MHC class II, and suggest that Fas deficiency may allow expansion of totally T-dependent B cells.

Co-stimulation and co-inhibition: equal partners in regulation

Specific immune responses are controlled by two counterbalancing mechanisms-co-stimulation and co-inhibition. Antigen receptors determine specificity, activate co-stimulation and/or co-inhibition, and interact with these co-stimulatory/co-inhibitory mechanisms to dictate the direction of the immune response, either positive or negative. Co-stimulatory or co-inhibitory ligands interact with their specific receptors and may indicate the context in which antigen is perceived by lymphocytes. Ligation of antigen receptors may activate only co-stimulatory or co-inhibitory mechanisms, and thus may influence secondarily the direction of the immune response. Furthermore, the activity of a given co-stimulator or co-inhibitory receptor is modified depending on signalling via the antigen receptor. If neither co-stimulators nor co-inhibitors are present, lymphocytes, activated in response to antigen receptor signalling, produce low levels of effector elements and then revert to inactivity. Co-inhibitors are defective in autoimmune disease.

Defective antigen-receptor-mediated regulation of immunoglobulin production in B cells from autoimmune strains of mice

B cells are stimulated by antigens or by polyclonal activators such as bacterial lipopolysaccharide (LPS) to produce antibody. In nonautoimmune strains of mice, LPS-stimulated antibody responses are inhibited by crosslinking the B cell antigen-receptor (BCR), while antigen-driven responses are shut down by co-crosslinking the BCR and the receptor for the Fc portion of IgG (Fc gamma R). BCR signals are poor at shutting off LPS-induced antibody production, including anti-ssDNA antibody production, in B cells from NZB, NZB/WF1, and BXSB lupus-prone mice but not MRL/lpr or NZW mice. In the current studies, the defect in NZB B cells was shown to be independent of T cells and macrophages. The inheritance pattern of resistance to BCR ligation of LPS-induced Ig production in BXSB mice could not be assigned to either founding strain. In New Zealand mixed (NZM) recombinant inbred mice, slightly but significantly more resistance was found in a line (NZM2410) that demonstrates a greater degree of clinical autoimmunity than another line (NZM64) with fewer autoimmune problems. The autoimmune defect is specific to BCR signals because inhibition of LPS activation by ligation of MHC class II occurs normally in NZB B cells. Bypassing the BCR by direct stimulation of second messengers with phorbol esters or ionomycin did not overcome the defect, suggesting that defects in downstream signaling events, rather than in the BCR mechanism itself, are responsible for the reduced ability to inhibit the LPS response in NZB B cells. The inability of the BCR signaling pathway to control LPS-induced Ig production in NZB mice was apparent at the level of H mu-chain mRNA for secreted IgM. These results suggest that autoimmunity-associated B cell defects in BCR signaling and subsequent regulation of LPS-driven antibody responses have a number of inheritance patterns and involve downstream events in signaling pathways in B cells. The defect can result in aberrant regulation of H mu-chain mRNA levels for secreted IgM production, and may be a predisposing factor in murine systemic autoimmune disease.

The trouble with transgenic mice

Observations on many antigen-receptor transgenic models with anti-self specificities have been interpreted as proof for clonal deletion or for mechanisms involved in clonal deletion. At the same time, there is increasing evidence that many lymphocytes that recognize self exist, are activated and produce end products, even in individuals without clinical autoimmunity. Except perhaps for the amount of anti-self activity, there is little agreement on what distinguishes immune products normally recognizing self from those associated with clinical autoimmunity. To resolve this paradox, the tendency in immunology is to accept conclusions from transgenic models as normal, while judging those from the unmanipulated state as suspect. However, transgenics have a major weakness. Transgenes encoding antigen-receptors are derived from highly selected mature lymphocytes and are expressed in developing lymphocytes that normally do not display the antigen-receptors of mature lymphocytes. Such precocious expression of antigen-receptors could have profound abnormal effects on lymphocyte development. Other transgenic models suggest that processes in lymphocyte differentiation not involving antigen-receptor binding specificity exert powerful influences on lymphocyte development; therefore, mechanisms other than classical positive and negative selection are important.

Do lymphocytes require calibration?

Complexity in the activation/regulatory apparatus and the variable nature of the antigen-binding site dictate that B and T cells establish and select, during their development, appropriate activation and control mechanisms beyond simple antigen-binding specificity. These mechanisms are established partly by fixed interactions dictated by genetically defined structures, but they are also attained by calibration during ontogeny. This calibration depends on the ordered expression of early components (each of which is invariant), on their interaction with specific ligands, and on the receipt of invariant signals for calibration. Lymphocytes calibrate themselves by expressing various cell surface components, such as restricted heavy chain D-regions and pseudo-light chains. These are expressed in association with elements that will make up the antigen-receptor complex of mature lymphocytes. Calibration by invariant signals results in the establishment, selection and active maintenance of cellular activities which serve to control lymphocyte function. Since these cellular activities are one of a number of possible conditions, they are referred to as variant controls. Effectively calibrated basic cellular functions, specialized responses and cellular interactions allow lymphocytes to attain self-nonself discrimination. If calibration fails, lymphocytes will develop abnormalities, such as immunodeficiency and autoimmunity.

Lipopolysaccharide-induced IgM production is not suppressed by antigen receptor ligation in B cells from some autoimmune strains of mice

Ligation of surface immunoglobulin on resting or activated nonautoimmune B cells inhibited lipopolysaccharide (LPS)-induced total IgM production. B cells from NZB, (NZB x NZW)F1, and BXSB mice were relatively resistant, but B cells from NZW or MRL/lpr mice were inhibited. The resistance occurs in B cells from young and old NZB mice, and in both resting and activated splenic NZB B cells. Anti-ssDNA responses induced by lipopolysaccharide occur in the presence of antigen-receptor-ligating antibody in NZB, but not in DBA/2, B cells. Antagonism in signaling between the antigen and LPS receptor is not a general B cell hyporesponsiveness, but defects in antagonism specifically between antigen and LPS signaling may be a predisposing factor to autoimmune disease in some autoimmune strains of mice.

Mutual antagonism between antigen- and lipopolysaccharide-induced antibody production

B cells are induced to antibody production by antigens or by mitogens, such as lipopolysaccharide (LPS). We observed a mutually antagonistic relationship between activation through the antigen-receptor (AgR) and LPS-receptor (LPSR) in vitro. Prior exposure of B cells to AgR-ligating antibody prevented antibody forming cell (AFC) production induced by LPS, but not that induced by specific antigen (SRBC, TNP-Ficoll, or TNP-LPS). AFC production induced by antigen could be abrogated by concomitant exposure to LPS; the shutdown of the antigen-driven response was apparent when LPS-induced AFC were prevented by pre-exposure to antibody against the AgR. The ability of signaling through the AgR to inhibit antibody production stimulated by LPS was seen in DBA/2 and BALB/c mouse strains, and not in the New Zealand Black (NZB) strain. The results suggest that mutual antagonism is distinct from other forms of immune hyporesponsiveness, and that defects in antagonism may be a factor in the development of autoimmune disease.

Immunoregulatory characteristics of the in vitro anti-ssDNA response

Continuous blockade of B-cell antigen receptors (BCRs) with Fab alpha sIg prevents the anti-ssDNA response of high, but not low, density B cells. Signaling via the BCRs, by prior exposure to crosslinking F(ab')2 alpha sIg, had no effect on the spontaneous anti-DNA response, but prevented a lipopolysaccharide-induced anti-DNA response. Pretreatment with intact alpha sIg, which provides exogenously derived Fc signals, reduced the response. An Fc-signal-blocking agent, F(ab')2 anti-IgG-Fc antibody, increased the number of anti-DNA antibody-forming cells produced in the absence of exogenous IgG anti-ssDNA antibody. Thus, activation is dependent on the availability of the BCRs, prior BCR crosslinking does not interfere with activation, and endogenous IgG anti-ssDNA antibody limits the activation of anti-ssDNA-specific B cells most of which are T-cell independent. These results indicate that the anti-ssDNA response is driven through the BCR.

Blockade of immunoregulatory Fc-signalling by HIV peptides: oligopeptides from HIV gp120 and gp41 bind the Fc portion of IgG and increase the in vitro anti-ssDNA response

Concomitant ligation of antigen receptors with Fc-receptors negatively signals B cells. Antibodies to the Fc portion of IgG prevent this negative Fc-signalling, provided that these antibodies do not emit Fc signals. Prevention of Fc signals leads to augmented antibody responses to self and foreign antigens, and reduces the requirement for T cells by 10- to 100-fold in T cell-dependent antibody responses. In ELISA assays, peptides from conserved portions of the glycoproteins, HIV-1 gp120 or gp41 from HIV-1 and HIV-2 bind to the Fc portion of IgG, but do not bind the F(ab')2 portion of IgG. HIV-derived peptides, which bind to the Fc portion of IgG, augment the antibody-forming cell response to single-stranded (ss)DNA. The spontaneous response to ssDNA using spleen cells from young mice, and the response in the presence of exogenous DNA using spleen cells from old mice, are augmented to the greatest extent. These results demonstrate that HIV peptides bind to the Fc portion of IgG and augment immune responses to DNA; they suggest the possibility that blockade of the Fc portion of IgG antibodies is associated with a reduction in Fc-mediated regulation of anti-self responses. Blockade of regulatory Fc-signalling may account for increased circulating immunoglobulins and autoantibodies in clinical AIDS.

Tentativeness and fervor in cell biology require negative and positive feedforward control

End-product feedback regulates early steps in metabolic pathways, affecting activation and the rate of end-product synthesis. Early formation of end-product also modifies later steps in the synthesis of end-product. We designate this form of regulation feedforward. Negative feedback/feedforward by end-products may result in homeostasis, but also in physiologic tentativeness. Positive feedback/feedforward by end-product gives rise to fervid events. Tentativeness and fervor, due to negative and positive feedforward rather than feedback, explain otherwise puzzling aspects of immunology and endocrinology.

Low-dose steroid therapy in cyclosporine-treated renal transplant recipients with well-functioning grafts. The Canadian Multicentre Transplant Study Group

OBJECTIVE

Low-dose prednisone given on alternate days as a steroid adjunct to cyclosporine therapy was investigated primarily for its influence on kidney graft and patient survival and, secondarily, on renal function and complications.

DESIGN

Multicentre randomized double-blind clinical trial.

SETTING

Fourteen Canadian transplant centres.

PATIENTS

A total of 523 patients with well-functioning renal transplants (cadaveric grafts or grafts from living related donors) and without active graft rejection reactions who were entered into the trial from 1982 to 1985.

INTERVENTION

Patients were randomly assigned 90 days after transplantation to receive either placebo (260 patients) or low-dose prednisone (263 patients).

MAIN OUTCOME MEASURES

Graft and patient survival.

MAIN RESULTS

After at least 5 years of follow-up 50 patients assigned placebo had lost their graft and 17 had died; the corresponding figures for those assigned prednisone were 38 and 16. After an average interval of 1.4 years 143 patients in the placebo group and 123 patients in the prednisone group had stopped therapy with the test drug or had had their treatment group decoded or both. Patients were withdrawn from the study 2 years after stopping the test therapy. The actuarial 5-year graft survival rates were 73% and 85% in the placebo and prednisone groups respectively (p = 0.03), and the actuarial 5-year patient survival rates were 92% and 94% respectively (p = 0.6). This analysis included 43 and 29 graft losses and 14 and 12 deaths in the placebo and prednisone groups respectively. Weibull parametric modelling of graft survival identified the following variables as risk factors for graft loss: histocompatibility leukocyte antigen B (HLA-B) mismatching (p = 0.007), donor death from cerebrovascular accident (p = 0.01), increased donor age (p = 0.02) and being a male recipient (p = 0.05). When these factors were included in the Cox proportional hazards model, the influence of assigned treatment on graft survival was reduced to p = 0.1. Donor death from cerebrovascular accident (p = 0.002), diabetes mellitus in the recipient (p = 0.02) and increased recipient age (p = 0.05) were risk factors for patient death. Renal function and incidence of complications were similar in the treatment groups.

CONCLUSIONS

Continued administration of low-dose prednisone on alternate days is advisable, particularly in patients with cadaveric grafts and those with previously failed transplants.

Regulation of an anti-self response: lack of influence of exogenous DNA on the in vitro anti-DNA response

Anti-DNA antibodies occur in outwardly normal individuals as well as in various forms of autoimmune disease. A number of publications have reported on the ability of added DNA to either induce or inhibit the in vitro production of anti-DNA antibody. In this study, the in vitro production of IgM anti-single stranded DNA (alpha ssDNA) antibody by spleen cells from normal or autoimmune mice neither depends upon, nor is inhibited by, the addition of high molecular weight DNA to the culture. The decrease in antibody forming cell plaques, reported previously, is due solely to the artifactual carryover of inhibitory material into the assay system, where it interferes with the expression of plaques by preventing anti-DNA antibody from reaching the DNA-coated erythrocytes. Similarly, plaque forming cell (PFC) methods have not detected alpha ssDNA antibody producing cells in murine spleen cells without culturing, but various other systems for measuring antibody normally detect anti-DNA antibodies in vivo. This discrepancy is also due to inadequate washing of freshly harvested cells to rid them of inhibitory substances which prevent them from registering as PFC. While S1 nuclease was able to prevent PFC interference by purified DNA, it did not remove the inhibitory substances from the culture supernatants; therefore substances other than ssDNA are able to interfere with alpha ssDNA PFC, suggesting that the alpha ssDNA PFC detected are polyspecific. Levels of alpha ssDNA PFC in spleen cells from non-autoimmune mice begin at one-quarter of the peak in vitro response, decrease to one-tenth in the first day and then reach peak values after 3 to 5 days of culture, suggesting that spleen cells are actively producing alpha ssDNA antibodies an in vivo and that then in vitro response is observed. Despite this evidence for an in vitro alpha ssDNA response, this response was not inhibited markedly by 1000 rad gamma-irradiation, while the response to sheep erythrocytes (SRBC) was profoundly suppressed. These findings suggest that anti-self B lymphocytes are resistant to interphase, possibly apoptotic, lymphocyte death due to gamma-irradiation, while anti-nonself B lymphocytes remain sensitive.

How many signals are enough?

The many signals that control the progress of various immune responses to both foreign and self antigens can be divided into no less than three major groups. The first group is the initial positive stimulus, associated with activation events through antigen receptors and their associated proteins. These signals launch lymphocytes in their response to antigen, either foreign or self. The second group of signals is negative and involves various end products and interactions between cells, all recognizing antigen. These signals are endogenous to the reacting cell, or nearly so (two interacting cells from the same clone, daughter cells, which are in the same locale and bind to the same ligand). The third group (the prevention of end product feedback, involving various forms of antigen presentation, T cell contributions, rheumatoid factor activity, and other mechanisms) is more likely to occur with nonself antigens, which are temporally and spatially more restricted than self antigens. Experimental evidence for this immunological schema is summarized and clarified in its relationship to the Bretscher-Cohn theory of self-nonself recognition and to suppressor cell and idiotype-antiidiotypic theories.

Lack of high avidity IgM anti-ssDNA antibodies in cells from autoimmune-prone and autoimmune mice

Non-autoimmune prone CBA mice were compared with autoimmune prone NZB, NZW, and (NZB x NZW)F1 mice for the ability of their splenic cells to produce anti-ssDNA-forming cells spontaneously in vitro, measured in the plaque forming cell assay. The number of antibody forming cells was measured and the relative avidity of antibody produced determined using a plaque inhibition assay. Splenic lymphocytes from young animals of a non-autoimmune strain (CBA/J) were shown to be capable of generating anti-ssDNA IgM antibody-forming cells in culture which displayed a higher avidity for antigen than that from autoimmune-prone or frankly autoimmune mice. Since an increased switching from IgM to IgG autoantibody production and defects in Fc-mediated signalling by IgG antibody have been identified in autoimmunity, we suggest that the metabolic block, normally in force in non-autoimmune-prone animals, accounts for this elevated avidity of IgM autoantibody.

Clonalism--the myth?

Two regulatory mechanisms, based on the contrasting concepts of imprinting (clonal theories and idiotypic networks) and of ongoing regulation of immune responses (by antigen and end products with specificity for antigen), give rise to different predictions and approaches to the question of autoimmunity and autoimmune disease. Both concepts have legitimacy, however, if a ranking in terms of explicative power must be given, ongoing regulation is more plausible since it accounts more fully for basic events in immune responses and in autoimmune phenomena. Many instructive findings have emerged from experiments based on this latter concept, furthermore, the approach has only received limited notice and, thus, has not yet been exhausted.

Rheumatoid factor blocks regulatory Fc signals

Immunosuppressed cultures of murine spleen cells, partly deprived of T cells and antigen-stimulated, can be reconstituted to near full activity in their antibody-forming cell response with murine rheumatoid factors (RF). The dose of RF required for recovery of 50% of the reconstitutable immune response was 10-100 ng and reconstitution was blocked by intact murine IgG added to the cultures. IgG subclass specificity of RF was demonstrated; RF specific for IgG2a was more potent than RF specific for IgG1 in reconstituting the response. Synergy was observed between RF added at culture initiation and late-acting B-cell differentiation factors. The greater the degree of T-cell deprivation, the more stringent the conditions needed for reconstitution. Suitable conditions for reconstitution with profound T-cell depletion included the limited reconstitution by specific RF, the synergistic action of RF with late-acting T-cell-replacing supernatants, and multiple additions of a number of RFs to the cultures on Days 0, 1, and 2. RF was also shown to block Fc-dependent immunosuppression by added antigen-antibody complexes. These results are interpreted as favoring the hypothesis put forward previously that the normal production of RF acts to reduce T-cell dependency by preventing negative Fc signal transmission by immune complexes on the B-cell surface. Abnormal production of RF may be a primary destabilizer of the immune responses leading to autoimmunity.

Rheumatoid factor and Fc signaling: a tale of two Cinderellas

Signaling to lymphocytes depends not only upon the interaction of receptors with specific antigen, but also upon antigen nonspecific receptors which receive input from two classes of molecules, immunologically specific end products and lymphokines. These represent the central elements in the physiologic stimulation of immune responses to both self and foreign antigens. This review is dedicated primarily to describing the function of physiologically active receptors for end product which are central to end product feedback in normal immune responses. The emergence of autoimmunity as a pathologic process resultant from a defective end product signaling mechanism is described.

Interference with Fc signals increases an antibody response by T-cell-deprived cultures to a T-dependent antigen

Affinity column purified goat anti-mouse immunoglobulin antibodies specific for the Fc portion of IgG increased an in vitro antibody response to a T-dependent antigen when T cells were limiting. Picogram amounts of specific anti-Fc antibody at culture initiation and nanogram quantities up to 3 days were required to demonstrate this effect. The demonstration of reconstitution by anti-Fc antibodies requires that the cultures be T-cell depleted and stimulated by antigen. These results support the concept that anti-Fc antibody and T cells block endogenously generated negative Fc signals.

Immune response after gastric bypass and weight loss

The immune response of 22 morbidly obese patients was measured before and 6 months after gastric bypass. In-vivo skin testing was carried out using five recall antigens. In-vitro response assessed the ability of isolated lymphocytes to take up radioactive thymidine after culture with the same antigens. The mean (+/- SD) preoperative weight of the patients of 122 +/- 14 kg declined by 33.5 +/- 8 kg after 6 months. The number of positive skin tests increased from a mean (+/- SEM) of 1.8 +/- 0.17 to 2.1 +/- 0.17 (p = 0.2). Mean (+/- SEM) induration of the skin-test response assessed at 24 hours after antigen injection increased from 4.7 +/- 0.6 mm to 5.5 +/- 0.6 mm (p = 0.35) and at 48 hours from 5.4 +/- 0.7 mm to 6.9 +/- 0.9 mm (p = 0.05). One patient who was anergic before gastroplasty responded normally 6 months later after substantial weight loss. In-vitro response, expressed as a stimulation index (+/- SEM), increased from 4.71 +/- 0.65 to 7.95 +/- 1.56 (p = 0.06) for the average of all antigens and from 12.85 +/- 2.05 to 15.79 +/- 2.84 (p = 0.2) for the largest response. The authors conclude that the response to test antigens in vitro and in vivo is not reduced significantly 6 months after gastric bypass and profound weight loss. Patients with severe vomiting, rapid weight loss or sepsis may respond differently and require individual assessment.

Inhibition of human in vivo cytotoxic T lymphocyte generation by cyclosporine following organ transplantation

The effect of cyclosporine (CsA) on the in vivo cell-mediated immune response to donor antigens was examined sequentially following cadaveric renal transplantation in both immunologically naive and specifically sensitized allograft recipients. Cytotoxic T lymphocytes (CTL) exhibiting preferential specificity for donor antigens were detected in the peripheral blood of all patients receiving azathioprine (AZA) immunosuppression by two weeks posttransplant, disappearing progressively over the first three months with clinical quiescence. In contrast, the generation of donor-reactive CTL was significantly diminished in incidence (P = 0.05) and in magnitude (P = 0.004) in subjects receiving CsA. CTL were detected in only 36% of patients by two weeks posttransplant, and were not detectable in any CsA-treated patient after the sixth posttransplant week. The ability of CsA to inhibit clonal reexpansion of CTL was examined both in vitro and in vivo in subjects exhibiting prior sensitization to donor antigens. In vitro, CsA caused a dose-dependent inhibition of accelerated (72-hr MLC) CTL generation following restimulation with donor spleen cells, which was quantitatively identical to that in parallel cultures using responder PBL from non-sensitized individuals. In vivo, CsA produced a rapid disappearance of circulating CTL posttransplant in patients who exhibited specific cell-mediated sensitization to the graft donor, as evidenced by the presence of circulating donor-reactive CTL prior to transplantation. In contrast, in patients receiving AZA there was a rapid increase in donor-reactive CTL in the peripheral blood following transplantation. CTL persisted for six weeks or longer, and two of four patients lost the graft to irreversible acute rejection within the first four weeks.

Immunological and pharmacological monitoring in the clinical use of cyclosporin A

Immunological reactivity to donor antigens and serum concentrations of cyclosporin A were monitored in six patients after renal transplantation. At concentrations of 0.1--1.0 microgram/ml cyclosporin A prevented both donor-specific immune reactivity and clinical rejection during the early post-transplant course. Measurement of cyclosporin A levels and immunological indices allowed individual adjustment of the dosage so as to give excellent early graft function with few adverse effects.