Augmentation of the antibody response in aged mice with an 8-derivatized guanosine nucleoside and its effect on immunological memory

The injection of aged mice with 7-methyl-8-oxoguanosine (7m8oGuo) along with aggregated human gamma-globulin (AHGG) results in an enhanced anti-HGG antibody response. Aged mice injected with AHGG alone make only a feeble anti-HGG response. The enhanced response in aged mice was not significantly different from the response obtained in young-adult mice injected only with AHGG. However, the enhanced response obtained by injection of 7m8oGuo in young-adult mice was several orders of magnitude greater than that observed in the aged mice. Aged mice given a primary injection of AHGG alone failed to make a secondary response to AHGG given 90 days later, whereas aged mice injected with 7m8oGuo along with a primary injection of AHGG showed variable secondary antibody responses to AHGG. Two of seven mice showed high degrees of immunological memory equivalent to that seen in young-adult mice while others showed either meagre or no responses. The effect of 7m8oGuo appeared to be primarily on B cells, albeit the role of T cells cannot be ruled out.     

Enhancement of the human antibody response by C8-substituted guanine ribonucleosides in synergy with interleukin 2

The antigen-specific primary antibody response of human lymphocytes in vitro was studied with respect to dependency upon the lymphokine interleukin 2 (IL 2) and its subsequent modulation by C8-substituted guanine ribonucleosides. The specific response to sheep erythrocytes was shown to be dependent on the presence of IL 2 in culture. However, addition of optimal concentrations of the nucleoside, 7-methyl-8-oxoguanosine (7m8oGuo), to cultures containing antigen and IL 2 resulted in marked amplification of the underlying antibody response. This synergistic effect between 7m8oGuo and IL 2 was antigen dependent and could not be accounted for by summation of the independent antigen-specific and nonspecific (polyclonal) components. That IL 2 itself was in fact responsible for both the specific response to antigen and the synergistic interaction with 7m8oGuo was confirmed in experiments with purified IL 2 produced by recombinant DNA technology. The response to antigen was enhanced by 7m8oGuo in a dose-dependent fashion. The results of kinetic studies demonstrated that this nucleoside is fully effective within the context of an ongoing immune response, because addition of 7m8oGuo could be delayed up to 3 days of the 6-day culture period without loss of subsequent immunoenhancement. Lymphocyte populations largely depleted of T cells were capable of mounting vigorous responses to antigen in the presence of 7m8oGuo so long as IL 2, either partially purified or purified recombinant material, was added to culture.     

Mechanism of 8-mercaptoguanosine-mediated adjuvanticity: roles of clonal expansion and cellular recruitment

The mechanism by which increased numbers of antigen-responsive B cells are generated in the presence of antigen and the C8-substituted guanine ribonucleoside, 8-mercaptoguanosine (8MGuo), has been investigated. Augmentation of the primary humoral response of splenocytes to antigen cannot be ascribed to the additive effects of the underlying antigen-specific response and the nonspecific (polyclonal) response induced by 8MGuo. This is clear from a consideration of the magnitude of the responses involved, as well as from a murine model (the SJL mouse) that does not generate a nonspecific response to the substituted nucleoside but responds to it with the usual degree of immunoenhancement in the presence of antigen. Other approaches suggest that two mechanisms are involved in adjuvanticity, one whereby preexisting antigen-specific B cells undergo clonal expansion, and one in which cells not normally participating in the response are recruited in the absence of clonal expansion. The latter mechanism appears to be the dominant one insofar as models in which 8MGuo-induced proliferation fails to occur (such as after irradiation, or in the SJL mouse) nonetheless exhibit strong adjuvant effects. Analysis of precursor frequency of antigen-specific B cells indicates that for each mature, antigen-responsive B cell present in adult murine spleen, an average of four additional cells can be recruited by the conjoint actions of antigen and 8MGuo. One group subject to such recruitment is the immature antigen-specific B cell, whose degree of functional maturity is accelerated in the presence of antigen and 8MGuo.     

Regulation of B cell activation by prostaglandins: cell cycle-specific effects on activation by anti-immunoglobulin and 8-mercaptoguanosine

The current studies were undertaken to explore the regulatory effects of macrophages and their soluble products on B cell activation in defined medium by surface membrane-directed mitogens (anti-Ig, LPS) and by intracellular mitogens (8-mercaptoguanosine, [8MGuo]). Supplementation of macrophage-depleted B cell cultures with adherent cells enhanced the response to anti-Ig but depressed the response to 8MGuo. These changes could be eliminated by adding indomethacin to B cell cultures containing supplemental macrophages. Moreover, they could be reproduced by adding exogenous prostaglandins (PGE1, PGE2) but not other macrophage products to cultured B cells. Prostaglandins regulate B cell function (i.e., immunoglobulin secretion) in the same manner as they do mitogenesis. Thus, the polyclonal response to LPS is enhanced, whereas that to 8MGuo is inhibited. We showed previously that anti-Ig acts on a B cell subpopulation distinct from that stimulated by 8MGuo. Moreover, when addition of prostaglandin is delayed for more than 24 hr, the effect on the anti-Ig response changes from enhancement to inhibition and the effect on 8MGuo is lost, suggesting that in the course of activation the cell progresses through a series of cell cycle-specific regulatory states. Additionally, the mitogenic effects of 8MGuo appear to involve larger, cycling cells more than smaller cells. In concert, these data suggest a model for regulation of the B cell cycle in which prostaglandins, whose secretion is elicited by many surface-directed B cell stimuli, enhance the entry of cells into the cell cycle and subsequently regulate their passage through the cycle.     

Lymphokine-like activity of 8-mercaptoguanosine: induction of T and B cell differentiation

Lymphocyte proliferation and differentiation result from ordered cellular interactions governed by soluble products (lymphokines). Dissecting the individual steps in these processes has been difficult, due to a paucity of pure lymphokines. Recently, it was reported that the derivatized ribonucleoside 8-mercaptoguanosine (8MGuo) has both mitogenic and differentiative effects on murine B cells. In the present studies, we tested 8MGuo for its ability to stimulate both B and T cell responses. In contrast to the murine studies, 8MGuo does not stimulate rat B cells to proliferate and, when tested for B cell growth factor-like activity, no stimulation was observed. The addition of 8MGuo (0.5 to 1 mM final concentration) to mitogen-stimulated B cells led to a marked increase in IgM and a modest increase in IgG secretion. When mixed with conditioned medium, 8MGuo acted synergistically in stimulating secretion of both isotypes, arguing that 8MGuo has both B cell-differentiating factor-mu (BCDF-mu) and BCDF-gamma activity. 8MGuo had no IL 2-like activity when tested on a mouse IL 2-dependent cell line, and no IL 1-like activity on addition to mouse thymocytes with or without submitogenic doses of lectin. However, when added to cultures of murine allogeneic cells in which the stimulating cell populations had been heat-inactivated, 8MGuo induced the generation of specific allogeneic cytotoxic T lymphocytes. Together, these results suggest that a simple derivatized nucleoside can induce both T and B cell differentiation without concomitant proliferation, and thus represent a unique probe for studying events in lymphocyte differentiation.     

The effect of aging on the induction of tolerance in a subpopulation of B lymphocytes

The present data further demonstrate that a subpopulation of B cells which were functionally deleted during aging can be revived in vivo with 7m8oGuo. This compound is a member of a family of derivatized ribonucleosides which are potent B-cell activators and adjuvants. Using this compound as a probe to revive aged hyporesponsive B cells of CBA/CaJ mice, it was demonstrated that a subpopulation of B cells functionally deleted by the aging process can be readily tolerized by DHGG in that they fail to respond to AHGG in the presence of 7m8oGuo. It appears that this compound directly affects the B cells, since it has previously been shown that another derivatized nucleoside with identical lymphocyte-modulating properties has no effect on Th cells once they have been tolerized to DHGG. B cells stimulated by the combined effect of AHGG and 7m8oGuo were more readily tolerized in aged than in young adult mice.     

Mechanism of synergy between T cell signals and C8-substituted guanine nucleosides in humoral immunity: B lymphotropic cytokines induce responsiveness to 8-mercaptoguanosine

B lymphocytes require a source of T cell-like help to produce antibody to T cell-dependent antigens. T cell-derived lymphokines and C8-substituted guanine ribonucleosides (such as 8-mercaptoguanosine; 8MGuo) are effective sources of such T cell-like help. Addition of T cell-derived lymphokines to antigen-activated B cells together with 8MGuo results in synergistic B cell differentiation, amplifying the sum of the individual responses twofold to four-fold. Lymphokine activity is required at initiation of culture for optimal synergy with 8MGuo, whereas the nucleoside can be added up to 48 hr after the lymphokines with full synergy. 8MGuo provides a perceived T cell-like differentiation signal to B cells from immunodeficient xid mice, thereby distinguishing a subset of Lyb-5- nucleoside-responsive B cells from those activated by soluble anti-mu followed by B cell stimulatory factor-1, interleukin 1, and B cell differentiation factors, which are Lyb-5+. Moreover, at least a subset of the B cells recruited by the synergistic interaction of lymphokines and nucleoside is distinct from that responsive to 8MGuo + antigen, insofar as Sephadex G-10 nonadherent xid B cells fail to respond to either 8MGuo or lymphokines alone, but do respond to the combination. A distinct subpopulation can also be demonstrated among normal B cells by limiting dilution analysis in which the precursor frequency of antigen-reactive B cells in the presence of lymphokines or nucleoside alone increases substantially when both agents are present together. In concert with the kinetic data, these observations suggest that synergy derives at least in part from the ability of lymphokines to induce one or more elements the absence of which limits the capacity of a distinct B cell subpopulation to respond to 8MGuo.     

Interaction between cytokines and 8-mercaptoguanosine in humoral immunity: synergy with interferon

In previous studies it has been demonstrated that a T cell-like differentiation signal is transmitted by C8-substituted guanine ribonucleosides such as 8-mercaptoguanosine (8MGuo) to antigen-stimulated B cells. A large subset of potentially reactive B cells remains unresponsive to antigen even in the presence of signals provided by these nucleosides except when this signal is preceded by a soluble activity present in mixed lymphocyte culture supernatants. Studies with purified preparations of interleukin (IL)-1, IL-2, IL-3, granulocyte-macrophage colony stimulating factor, B cell stimulatory factor 1 (IL-4), and B cell growth factor II (IL-5) indicated that none of these activities is capable of synergizing with 8MGuo to augment B cell responsiveness to antigen. Therefore, supernatants from a number of cloned cell lines were examined for activity that could synergize with 8MGuo, in order to determine the cellular source of this activity. Soluble products secreted by cloned 24/G1 T cells act synergistically with 8MGuo to evoke enhanced antibody responses to specific antigen in populations of purified B cells. Because concanavalin (Con) A-activated 24/G1 cells produce large quantities of interferon-gamma (IFN-gamma), the possibility that interferons might mediate synergy with 8MGuo was investigated. Purified murine IFN-gamma is unable to interact synergistically with 8MGuo; moreover, treatment of active 24/G1 supernatants with monoclonal anti-IFN-gamma antibodies or at pH 2 fails to abrogate their ability to synergize. In contrast to IFN-gamma, when B cells were supplemented with either IFN-alpha or IFN-beta, antigen-dependent synergy with 8MGuo was observed. However, abrogation of IFN-alpha and IFN-beta activity with specific antibodies fails to interfere with synergy between 8MGuo and mixed lymphocyte culture or Con A supernatants. Therefore, it appears that although IFN-alpha and IFN-beta are not responsible for the synergizing activity present in activated T cell supernatants, they nonetheless represent a previously unrecognized source of synergizing activity.     

The effect of lipopolysaccharide desensitization on the regulation of in vivo induction of immunologic tolerance and antibody production and in vitro release of IL-1

As previously reported, LPS and 8-derivatized guanosine (both generators of IL-1 release), as well as IL-1 itself interfere with the in vivo induction of tolerance to DHGG in A/J mice. In the present studies it was demonstrated that desensitization of either A/J or CBA/CaJ mice with LPS aborts the ability of LPS to interfere with the induction of tolerance to DHGG. The abrogation of the ability of LPS to interfere with tolerance by LPS desensitization is not the result of neutralization of LPS by antibody produced to LPS during desensitization. Desensitization with LPS also aborts the interference with tolerance induction by 7-methyl-8-oxoguanosine. LPS desensitization inhibits the ability of LPS and/or 7-methyl-8-oxoguanosine to both convert a tolerogenic signal to an immunogenic signal and interfere with the induction of a tolerant state to a subsequent injection of Ag. The effects resulting from desensitization may be in part attributed to the depletion of IL-1. LPS desensitization also modulates the antibody response to injection of the AG, AHGG. Desensitization with LPS markedly suppresses the antibody response to a subsequent injection of AHGG in CBA/CaJ mice. Desensitization with LPS also inhibits the anti-HGG antibody response in A/J mice, but in this strain its effect is dependent on the route of injection of AHGG. In an experiment directly comparing the responses of normal and desensitized A/J mice to either intravenous or intraperitoneal injection of AHGG, desensitization only suppressed the response in mice injected with AHGG i.p.. Desensitization with LPS also inhibits the ability of LPS to act as an adjuvant in a subsequent antibody response to AHGG. Not only does desensitization interfere with the primary antibody response to AHGG, but it also interferes with the secondary response, suggesting that the primary injection after desensitization induces a state of immunologic tolerance.     

T cell-replacing activity of C8-derivatized guanine ribonucleosides

The capacity of the C8-substituted guanine ribonucleosides to provide T cell-like signals to cultures of splenic B cells was evaluated. We showed previously that these low m.w. nucleoside derivatives traverse the cell membrane and induce their effects from an intracellular location. The current studies clearly demonstrate that 8 mercaptoguanosine (8MGuo), when added to cultures of B cells and macrophages in the presence of antigen, is capable of supplying a "second signal" for B cells, enabling them to generate high numbers of specific plaque-forming cells against the immunizing antigen. This effect is duplicated in cultures of spleen cells from congenitally athymic mice. Inhibition of interleukin 2 (IL 2) generation by cyclosporin A, such that the antibody response of normal spleen cells is entirely abrogated, has minimal effects on the T cell-replacing activity of 8MGuo. Additivity studies with MLC supernatants as well as kinetic analyses with IL 2-associated lymphokines substantiate that these factors act by a mechanism distinct from that of 8MGuo and 8BrGuo. These observations establish these nucleoside activators as exciting new probes for T helper cell activity and an effective non-T cell source of T cell-like signals.     

Demonstration of T-cell-dependent and T-cell-independent components of 8-mercaptoguanosine-mediated adjuvanticity

The contribution of T cells to potentiation of humoral immunity by the C8-substituted guanine ribonucleosides and the origin of the increased numbers of antigen-responsive B cells generated consequent to their action have been investigated. Augmentation of the antigen-specific antibody response by these nucleosides, exemplified by 8-mercaptoguanosine (8MGuo), can be separated into T-cell-dependent and T-cell-independent components, both by use of the T-cell tropic immunosuppressive agent, cyclosporin A, and by experiments using separated populations of T and B cells. Augmentation of adjuvanticity by T cells is hypothesized to involve a B-cell subpopulation not otherwise subject to the action of 8MGuo. This subpopulation could potentially arise by either of two mechanisms, one whereby preexisting antigen-specific B cells undergo clonal expansion, and one in which cells not normally participating in the response are recruited in the absence of clonal expansion. Although the former mechanism makes a minor contribution to adjuvanticity, the latter mechanism appears to be the dominant one, insofar as models in which 8MGuo-induced proliferation fails to occur (such as after irradiation, or in the SJL mouse) nonetheless exhibit strong adjuvant effects. Analysis of precursor frequency of antigen-specific B cells indicates that for each mature, antigen-responsive B cell present in adult murine spleen, an average of four additional cells can be recruited by the conjoint actions of antigen and 8MGuo. One group subject to such recruitment is the immature antigen-specific B cell, whose degree of functional maturity is accelerated in the presence of antigen and 8MGuo.     

Potent CTL induction by a whole cell pertussis vaccine in anti-tumor peptide immunotherapy

Promising yet limited clinical responses have been reported for peptide based immunotherapy against tumors. In order to induce more potent cytolytic CD8 T cell responses, we investigated the use of Bordetella pertussis vaccine as an adjuvant for peptide immunization. A whole cell (Wc) vaccine has been known to induce a Th1 biased immune response while an acellular (Ac) vaccine tends to induce that of the Th2 type. Natural infection by B. pertussis helps to maintain a robust Th1 memory in the host population. To examine the adjuvant activity of the pertussis vaccine, we immunized mice with an ovalbumin peptide as a model tumor antigen, and monitored the development of anti-tumor activities. The addition of either the Ac or the Wc vaccine helped expand the specific CD8 T cells. However, there was a marked difference in the induced cytolytic activity where the Wc vaccine was superior to the Ac. The Wc vaccine was also more effective in inducing in vivo tumor rejection. The adjuvant activity was not only effective against ovalbumin, but was also evident when an endogenous tumor antigen, Wilms' tumor 1 gene product, was targeted. These results indicate that, although the Wc vaccine does not share the same antigen specificity with tumor cells, it can aid in the development of highly cytolytic CD8 T cells as an adjuvant at the site of peptide immunization.     

8-Mercaptoguanosine overcomes unresponsiveness of human neonatal B cells to polysaccharide antigens

We have shown previously that pneumococcal polysaccharides behave as human T cell-independent type 2 Ag. When cultured in vitro with type 4 pneumococcal polysaccharides (PS4), human neonatal B cells do not or only marginally respond. Limiting dilution analysis of neonatal B cells polyclonally activated by a combination of phorbol esters, calcium ionophore, and T cells and T cell factors, however, showed that Ag-reactive B cells are present in cord blood. The frequency of anti-PS4 reactive B cells in cord blood is comparable with that of adult peripheral blood. In order to obtain more insight into the activation requirements of these PS4-reactive neonatal B cells, 8-mercaptoguanosine (8MGuo) was added to in vitro cultures. Addition of 0.5 to 1.0 mM 8MGuo resulted in a 3- to 10-fold amplification of the anti-PS4 response. the effect of 8 MGuo was most prominent when added 3 days after initiation of the culture. Based on kinetic studies, we propose that in vitro activated cells are target for 8MGuo. These data further indicate that neonatal unresponsiveness to polysaccharide Ag is not due to the physical absence of Ag-reactive B cells but more likely to be the consequence of different activation requirements as compared with adult B cells.     

Activation of lymphocytes by a thiol-derivatized nucleoside: characterization of cellular parameters and responsive subpopulations

Lymphocyte activation, whether specific or nonspecific, is generally conceptualized as initiated by the binding of an activating ligand to a surface membrane receptor, followed by transduction of the signal across the cell membrane. In many situations several qualitatively distinct signals are required. We have recently described a new class of lymphocyte activator, the C8 bromine substituted guanine ribonucleosides, that traverse the cell membrane, bypassing classical triggering mechanism(s), apparently activating the lymphocyte at an intracellular site. However, the identity of the lymphocyte population(s) activated, as well as the nature of any cellular interactions involved in activation, has not been studied heretofore. The present experiments describe the cellular parameters of lymphocyte activation by a thiol substituted member of this class of activators, 8-mercaptoguanosine (8MGuo). Upon addition of this nucleoside derivative to cultures of murine spleen cells, a marked increase in [3H]TdR uptake and blast transformation ensues. Normal splenic B cells and spleen cells from congenitally athymic (nu/nu) mice are responsive to 8MGuo, whereas thymocytes and splenic T cells are not. Two subpopulations of B cells appear to be involved in the response to this nucleoside. The predominant one is a mature population that bears surface delta-chains, la antigens, C receptors, and (by indirect evidence) the Lyb3, 5, and 7 antigens. These cells also bear mu-chain and Fc receptors. In addition, a second, minor subpopulation of less mature cells that bear only mu-chain and Fc receptors also appears to be reactive to 8MGuo. The existence of this immature, reactive B cell subset was confirmed by observation of 8MGuo responsiveness in lymphocytes from 4-day-old mice whose cells do not yet exhibit these later-appearing markers. Accessory cells appear to play a minimal, if any, role in the 8MGuo response. These results establish two distinct B cell subpopulations as the major and minor cellular targets of C8-derivatized nucleosides, and suggest that the activation process results from a direct interaction between the nucleoside and target cell.     

Regulation of DNA-raised immune responses by cotransfected interferon regulatory factors

Interferon regulatory factor 1 (IRF-1), IRF-3, and IRF-7 have been tested as genetic adjuvants for influenza virus hemagglutinin (HA) and nucleoprotein vaccine DNAs. Cotransfection of HA with IRF-3 and IRF-7 increased CD4 T-cell responses by 2- to 4-fold and CD8 T-cell responses by more than 10-fold. Following intramuscular deliveries of DNA, both CD4 and CD8 T cells were biased towards type 1 immune responses and the production of gamma interferon. Following gene gun bombardments of DNA, both were biased towards type 2 immune responses and the production of interleukin-4. The biases of the T-cell responses towards type 1 or type 2 were stronger for immunizations with IRF-3 as an adjuvant than for immunizations with IRF-7 as an adjuvant. Moderate adjuvant effects for antibody were observed. The isotypes of the antibody responses reflected the method of DNA delivery; intramuscular deliveries of DNA predominantly raised immunoglobulin G2a (IgG2a), whereas gene gun deliveries of DNA predominantly raised IgG1. These biases were enhanced by the codelivered IRFs. Overall, under the conditions of our experiments, IRF-3 had good activity for T cells, IRF-7 had good activity for both antibody and T cells, and IRF-1 had good activity for antibody.     

TRF requirements for in vitro PFC responses to SRBC and R36a. I. TRF is distinct from IL 2 but indistinguishable from polyclonal BCSF

In vitro PFC responses to the thymus-independent (TI) antigen Streptococcus pneumoniae R36a require T cell replacing factor(s) (TRF). This requirement for TRF is as significant as for the thymus-dependent (TD) antigen SRBC. TRF is shown to be distinct from IL 2 by the following observations: 1) culture supernatants from the cloned T cell line L2, collected over an 8-day period after allogeneic stimulation, transiently contain IL 2 activity but maintain high levels of TRF activity throughout 192 hr; 2) L2V, a variant subclone of L2, produces much higher levels of TRF activity than the parental line but no detectable IL 2 activity; 3) the addition of IL2+, TRF- supernatants from the T cell hybridoma FS6-14.13 does not affect the L2V SF-driven PFC responses to R36a or SRBC; and 4) the addition of contaminating T cells to cultures containing T cell-depleted spleen cells, L2V SF, and antigen does not affect the PFC response. TRF does appear to be indistinguishable from polyclonal B cell stimulating factor (BCSF), which stimulates polyclonal PFC responses in the absence of antigen, mitogen, or anti-Ig. The TRF and BCSF activities of L2V SF could not be separated by ion-exchange, hydrophobic-interaction, and gel-filtration chromatography. TRF and BCSF have an apparent m.w. of approximately 40,000.     

Effects of cyclic nucleotides on ornithine decarboxylase activity in mammary gland explants from mid-pregnant mice

Dibutyryl cAMP and prolactin stimulated ornithine decarboxylase activity in mouse mammary gland explants which had been preincubated with insulin and cortisol for 1 day; maximally stimulatory concentrations of dibutyryl cAMP and prolactin produced a response which was greater than the sum of the responses of prolactin and dibutyryl cAMP when tested alone. 8-Bromo-cGMP inhibited ornithine decarboxylase activity whereas other derivatives of cyclic nucleotides were without effect. Cortisol concentrations were found to be important for optimizing the dibutyryl cAMP and prolactin responses. Optimal prolactin responses were obtained with cortisol concentrations greater than 10(-7) M, whereas optimal dibutyryl cAMP responses were observed with cortisol concentrations less than 10(-7) M. Despite the differing optimal cortisol concentrations for the prolactin and dibutyryl cAMP responses, it is concluded that prolactin and dibutyryl cAMP probably stimulate ornithine decarboxylase activity in the mammary gland via the same mechanism.     

Mitogenic responses of peripheral blood mononuclear cells of vervet monkeys (Cercopithecus aethiops): Apparent role of adherent cells

Peripheral blood mononuclear cells (PBM) from normal vervet monkeys (Cercopithecus aethiops) were examined for blastogenic responses to concanavalin A (ConA), phytohemagglutinin (PHA), and pokeweed mitogen (PWM). The mitogen stimulated PBM in a dose-dependent manner. Response to ConA was apparently higher than for the other two mitogens. Cell density and mitogen concentration were critical parameters for optimal lymphocyte proliferation, an observation in line with that reported for other mammalian species. Depletion of an adherent cell population probably of monocyte/macrophage lineage from vervet PBM gave higher proliferative responses to both ConA and PHA, but the response without adherent cells to ConA was greater than the response without adherent cells to PHA. This latter finding is in contrast to what has been reported in many other species.     

A novel guanosine analog, 7-thia-8-oxoguanosine, enhances macrophage and lymphocyte antibody-dependent cell-mediated cytotoxicity

Intraperitoneal treatment of mice with a novel guanosine analog, 7-thia-8-oxoguanosine (7-thia-8-oxoGuo), gives rise to activated splenic lymphocytes and peritoneal macrophages with enhanced capacity to mediate antibody-dependent cellular cytotoxicity (ADCC). ADCC activities against both chicken red blood cells and P815 murine plasmacytoma cells were enhanced, indicating that macrophages as well as lymphocytes functioning as K-cells in the two distinct cytolytic systems, were activated by 7-thia-8-oxoGuo. Furthermore, 7-thia-8-oxoGuo enhanced lymphocyte-mediated ADCC activity in beige (bgJ/bgJ) mice against P815, thus indicating the ability of 7-thia-8-oxoGuo to function as a potent immunomodulator even in an animal that is known to possess selective impairment of naturally occurring killer lymphocytes. These results suggest that 7-thia-8-oxoGuo could serve as an agent for immunomodulation and immunorestoration.