Suppression Of Antibody Production Research Articles

Immune system in vasopressin-deficient rats during ontogeny.

Morphofunctional immune disorders were revealed in vasopressin-deficient Brattleboro rats with diabetes insipidus during ontogeny. We observed a permanent decrease in the number of blood lymphocytes, increase in neutrophil count, reduced activity of macrophages, early involution of the thymus and spleen, and suppression of antibody production. These changes reflect impaired general resistance of these animals.

Immunoglobulin E is not required for but enhances airway inflammation and hyperresponsiveness.

The aim of this study was to investigate the role of immunoglobulin E (IgE) in the late phase reaction (LPR) of murine experimental asthma. Our model consisted of an implant of DNP-conjugated, heat-coagulated hen's egg white (DNP-EWI), followed 14 days later by an intratracheal challenge with aggregated DNP-ovalbumin. Airway inflammation was analyzed 48 h after challenge and compared with a similarly immunized group of mice with highly suppressed humoral response due to anti-micro and anti-delta antibody treatment. Total number of cells in the bronchoalveolar lavage (BAL) (with predominance of eosinophils) and EPO activity in the lung homogenate were increased in the DNP-EWI-immunized group compared with immunosuppressed or nonimmunized mice. However, the cellular infiltration and EPO activity observed in the immunosuppressed group were still significantly above those obtained in the nonimmunized group, indicating that inhibition of antibody production did not completely prevent the inflammatory manifestations in BAL and lung. Airway hyperresponsiveness to methacoline was obtained in DNP-EWI-immunized mice, but the respiratory mechanical parameters returned to normal levels in the immunosuppressed group. When these mice were reconstituted with monoclonal anti-DNP antibodies, only IgE, but not IgG1, restored lung inflammation and decreased the conductance of the respiratory system, therefore, increasing hyperresponsiveness. These results indicate that antibodies are not essential for induction of LPR in the lung. However, IgE enhances pulmonary inflammation and hyperresponsiveness.

Commentary on pretransplantation: removing immunologic barriers

G iven a rather static number of deceased organ donors in the United States, finding enough cadaveric organs to meet the ever-increasing demand for transplantation seems unlikely in the foreseeable future. Already, kidneys from living donors have increased 3-fold over the last decade, accounting for almost half of all renal allografts in the United States in 2002.1 As many as 15% to 20% of those on the waiting list may have potential live donors that were not used because of major histocompatibility complex presensitization or ABO incompatibility. It now appears that these previously insurmountable barriers may actually be amenable to novel therapies that reduce their impact. In the first study, Sonnenday and colleagues report on 33 patients who received successful kidney transplants from live donors at The Johns Hopkins Hospital despite presensitization. With careful immunologic monitoring, aggressive preconditioning, and a high level of posttransplant surveillance, success rates were quite high. Even recipients who experienced antibody-mediated rejection ultimately maintained excellent allograft function over 12 to 18 months. In the second study (randomized and placebo controlled), Jordan and colleagues used highdose intravenous immunoglobulin to successfully desensitize transplant candidates with a mean panel reactive antibody level of 81%. Thirty-seven percent of these patients received subsequent transplants, with excellent outcomes. In the third study, Tanabe and colleagues continue to refine their experience with ABO-incompatible transplants in Tokyo, achieving long-term graft survival in almost all cases with a protocol that includes plasmapheresis, intravenous immunoglobulin, splenectomy, and pretransplant immunosuppression. Although more costly to perform than a standard transplant, successful engraftment after desensitization is still substantially less expensive over time than remaining on dialysis. These new approaches reflect the impact of several recent advances. First, better laboratory techniques enable easier identification and quantification of ABO and specific anti-HLA antibody.2 Second, greater precision in histologic diagnosis of antibody-mediated events within the allograft is now possible because of advances that include C4d staining.3 Third, availability of effective immunosuppression with tacrolimus, mycophenolate mofetil, and corticosteroids appears to suppress antibody production after transplantation.4 The ongoing organ shortage almost mandates increasing application of these protocols in coming years if we are to increase availability of kidney transplantation to those who have no other alternative to a prolonged wait on dialysis.

T cell receptor transgenic mice provide novel insights into understanding cellular targets of TCDD: suppression of antibody production, but not the response of CD8 + T cells, during infection with influenza virus

Although exposure to 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) clearly impairs T cell-dependent immune responses, the mechanisms underlying TCDD-induced T cell dysfunction are unclear. With the goal of determining precisely how exposure to TCDD impairs the activation of CD8 + T cells in vivo, we used a well-defined T cell receptor (TCR) transgenic system. Greater than 95% of the CD8 + T cells in F5 transgenic mice possess TCR specific for a peptide from influenza A virus expressed in the context of H-2D b. Unexpectedly, we discovered that exposure to TCDD did not alter CD8 + T cell function in the transgenic mice. Specifically, treatment of F5 mice with TCDD did not affect the recruitment of virus-specific CD8 + T cells to the lung, nor did it impair the ability of CD8 + T cells in the lymph node to produce cytokines, or to clonally expand or differentiate. This is in direct contrast to the suppressive effects of TCDD on the response of CD8 + T cells in wild-type mice. Exposure of F5 mice to TCDD induced CYP1A1 and suppressed the production of virus-specific antibodies. Likewise, upon adoptive transfer into wild-type mice, TCDD suppressed the expansion and differentiation of F5-derived CD8 + T cells. This indicates that the F5 mice and lymphocytes derived from them are not inherently resistant to the immunosuppressive effects of TCDD. Rather, our data suggest that in the context of a supraphysiological number of antigen-specific CD8 + T cells, the function of these cells was not affected by exposure to TCDD. Given that antibody production in the F5 mice was sensitive to suppression by TCDD, while the CD8 response was resistant, our data provide a new perspective on the ways in which exposure to TCDD adversely affects B and T lymphocyte function.

Treatment of patients with haemophilia and inhibitory antibodies.

The development of inhibitory antibodies is a complication which arise in approximately 10% of patients with haemophilia A. The underlying genetic mutation is the single most important predisposing cause, although other risk factors have been identified. Periodic screening for inhibitors is a vital aspect of haemophilia care. The consequences of inhibitor development are very significant in terms of morbidity and cost. Several agents are now available for control of bleeding, but these are often very expensive. The most useful agents include recombinant activated factor VII, prothrombin complex concentrates and porcine factor VIII. It is possible to suppress antibody production with immune tolerance, which is successful in approximately 85% of cases and relapse is rare.

Treatment with a short course of LF 15-0195 and continuous cyclosporin A attenuates acute xenograft rejection in a rat-to-mouse cardiac transplantation model.

Searching for a novel immunosuppressive agent to effectively prevent acute vascular rejection (AVR) is essential for success in clinical xenotransplantation. We previously reported that Lewis rat hearts transplanted into BALB/c mice developed typical AVR in 6 days. The present study was undertaken to determine the efficacy of LF 15-0195, a new immunosuppressive analog of 15-deoxyspergualin in the prevention of AVR in a rat-to-mouse cardiac xenograft model. We transplanted 2-week old Lewis rat hearts into BALB/c mice. Four groups were included in this study: untreated recipients and cyclosporin A (CsA) treated recipients were controls; LF 15-0195 treated recipients or LF 15-0195 combined with CsA treated recipients were experimental groups. Mouse recipients received either LF 15-0195 2 mg/kg subcutaneously from day-1 to post-operative day 14, or CsA 15 mg/kg subcutaneously daily, from day 0 to endpoint rejection, or the two drugs in combination. We observed that high dose CsA did not inhibit AVR and the graft was rejected in 11.3 +/- 1.9 days. Graft histology and immunohistology showed typical AVR, characterized by interstitial hemorrhage, intravascular fibrin deposition, thrombosis, and massive deposition of anti-rat immunoglobulin G (IgG) and immunoglobulin M (IgM). Serum xenoreactive antibodies (xAbs) were markedly elevated in these animals as well. In contrast, we observed that treatment with LF 15-0195 alone significantly prolonged graft survival to 19.3 +/- 0.7 days. Notably, xAbs were significantly decreased and the rejection pattern of these grafts was cell-mediated rejection (CMR), instead of AVR. When CsA was combined with LF 15-0195, the graft mean survival time was further increased to 58.5 +/- 17.3 days. Antibody production and T-cell infiltration were significantly inhibited at the terminal stages of graft survival and pathology showed striking attenuation of both AVR and CMR. Sequential studies on days 6 and 14 demonstrated that LF 15-0195 either alone or combined with CsA completely inhibited antibody production. However, intragraft infiltration by Mac-1 positive cells including natural killer cells, macrophages and granulocytes in LF 15-0195 treated recipients was similar to that of untreated recipients. We conclude that LF 15-0195 effectively prevented AVR by markedly inhibiting the production of anti-donor IgG xAbs. Also, treatment with short course LF 15-0195 and continuous CsA significantly reduced T-cell infiltration. Studies to test this therapy in inhibiting AVR in a pig-to-non-human primate xenotransplantation model are underway.

Attenuation of acute xenograft rejection by short-term treatment with LF15-0195 and monoclonal antibody against CD45RB in a rat-to-mouse cardiac transplantation model.

We previously reported that Lewis rat hearts transplanted into BALB/c mice developed typical acute vascular rejection (AVR). The present study was undertaken to determine the efficacy of LF15-0195, a new analogue of 15-deoxyspergualin, in the prevention of AVR and to determine whether a combination of LF15-0195 and CD45RB monoclonal antibody (mAb) would have a synergistic effect in prolonging xenograft survival. We transplanted 2-week-old Lewis rat hearts into BALB/c mice, followed by experimental immunosuppressive regimens. Control groups were either untreated or treated with mAb monotherapy (100 microg/mouse, days -1 to 7, intravenously). Experimental groups were either treated with LF15-0195 (2 mg/kg, days -1 to 14, subcutaneously) or with LF15-0195 combined with mAb at monotherapeutic doses. Heart xenografts in both untreated and mAb-treated BALB/c recipients were rejected at 6.0+/-0.7 days and 8.5+/-1.3 days, respectively, with typical features of AVR, characterized by hemorrhage, fibrin deposition, thrombosis, and massive accumulations of anti-rat IgG and IgM. Serum xenoreactive antibodies (xAbs) were also markedly elevated in these animals. In contrast, LF15-0195 monotherapy significantly prolonged graft survival to 19.3+/-0.7 days. Notably, xAbs were significantly decreased and graft rejection was of a cell-mediated nature instead of AVR. When mAb was combined with LF15-0195, graft survival was further increased to 65.2+/-9.1 days. Antibody production and T-cell infiltration were significantly inhibited at terminal stages of graft survival. Sequential studies on days 6 and 14 demonstrated that LF15-0195, either alone or combined with mAb, completely inhibited antibody production. However, intragraft infiltration by Mac-1+ cells in LF15-0195-treated recipients was similar to that of untreated recipients. LF15-0195 effectively attenuated AVR by markedly inhibiting antidonor xAb production. Treatment with a combination of LF15-0195 and CD45RB mAb also significantly reduced T-cell infiltration and should be studied further to evaluate its efficacy in nonhuman primate subjects.

Antigen-specific, CD4+CD25+ regulatory T cell clones induced in Peyer's patches.

Since intestine is exposed to numerous exogenous antigens such as food and commensal bacteria, the organ bears efficient mechanisms for establishment of tolerance and induction of regulatory T cells (T(reg)). Intestinal and inducible T(reg) include T(r)1-like and T(h)3 cells whose major effector molecules are IL-10 and transforming growth factor (TGF)-beta. These antigen-specific T(reg) are expected to become clinical targets to modify the inflammatory immune response associated with allergy, autoimmune diseases and transplantation. In the present study, we characterized the antigen-specific T(reg) induced in the intestine by orally administering high-dose beta-lactoglobulin (BLG) to BALB/c mice. Seven days after feeding, only Peyer's patch (PP) cells among different organs exerted significant suppressive effect on antibody production upon in vitro BLG stimulation. This suppressive effect was also prominent in six BLG-specific CD4(+) T cell clones (OPP1-6) established from PP from mice orally administered with high doses of BLG and was partially reversed by antibodies to TGF-beta. Intravenous transfer of OPP2 efficiently suppressed BLG-specific IgG1 production in serum following immunization, indicating the role of such T(reg) in the systemic tolerance after oral administration of antigen (oral tolerance). OPP clones secrete TGF-beta, IFN-gamma and low levels of IL-10, a cytokine pattern similar to that secreted by anergic T cells. OPP clones bear a CD4(+)CD25(+) phenotype and show significantly lower proliferative response compared to T(h)0 clones. This lower response is recovered by the addition of IL-2. Thus, antigen-specific CD4(+)CD25(+) T(reg), which have characteristics of anergic cells and actively suppress antibody production are induced in PP upon oral administration of protein antigen.

DSLET and ACTH(4-10) increase mitotic activity of hepatocytes and suppress antibody production.

The mitotic index of hepatocytes remained unchanged after 10 intraperitoneal injections of DSLET and ACTH(4-10) in doses of 0.5, 1.5, and 5 microg/kg, but increased after injection of these substances in doses of 50 and 150 microg/kg. DSLET in doses of 5, 50, and 150 microg/kg decreased the number of antibody-producing cells in the spleen. ACTH(4-10) possessed immunosuppressive activity not only in these doses, but also in a dose of 1.5 microg/kg. As differentiated from mitotic activity of hepatocytes, the degree of immunosuppression increased with increasing the dose of test peptides.

Losing Their Grip

To battle infections, the immune system has to recognize and grab invaders. New work suggests that with age, certain immune cells lose their hold on the molecules that identify trespassers. The study identifies for the first time a molecular defect in these cells that could weaken older immune systems. Elderly people succumb to infections such as influenza more easily than do youngsters, and they don't develop the large numbers of specific antibodies that usually arise from repeated exposure to microbes or from vaccinations. Why age undercuts the immune system isn't clear, but researchers know that people's immune systems gradually lose the ability to generate B cells, which produce antibodies against interlopers. Antibodies bind antigens--bits of bacteria and viruses--and bring them to lymph nodes and the spleen, where follicular dendritic cells (FDCs) grab onto this so-called immune complex. FDCs then shuttle the complex to B cells, which produce a second round of antibodies with the help of T cells. The new batch of antibodies prods other immune cells to destroy the interlopers and provide resistance to future infections. Previously, Andras Szakal, an immunologist at Virginia Commonwealth University in Richmond, and colleagues found that FDCs from old animals lose their antigen-antibody-binding power. The team set out to find molecular changes that underlie the deterioration. The team first compared FDCs from old and young mice. Animals carried similar numbers of FDCs regardless of age, but cells from old animals displayed fewer copies of the cell surface receptor that they use to pick up immune complexes. Then the researchers assessed the ability of FDCs to stimulate antibody production in a culture dish. They combined FDCs from either 12-week-old or 26-week-old mice with B cells and T cells from 12-week-olds. After exposure to a test antigen, young FDCs spurred far greater antibody output than did old FDCs. Furthermore, old B and T cells churned out antibodies as well as their younger counterparts did in the presence of young FDCs. The team is currently investigating how FDCs regulate the amount of the cell surface receptor; boosting quantities of this molecule might bolster flagging immunity. "FDCs might be a bottleneck in the aging immune system," says Szakal. The results suggest that an age-related loss of receptors on the surface of FDCs prevents the cells from shepherding antigens to B and T cells and, as a result, suppresses antibody production. "I was taken aback," says immunologist Dennis Taub of the National Institute on Aging's branch in Baltimore, Maryland. Previous studies have shown that B and T cell function declines with age, but the new work "suggests that the FDCs themselves are responsible for the age-based loss of immune function." Not everyone is convinced. Although FDCs might play a role, the study doesn't clear B and T cells, says immunologist Robin Callard of University College London, because the cell culture studies might not re-create what happens in an intact animal. Still, the elderly might defeat infections if scientists can find a way to make their FDCs maintain a tight hold on transgressors. --R. John Davenport Y. Aydar, P. Balogh, J. G. Tew, A. K. Szakal, Age-related depression of FDC accessory functions and CD21 ligand-mediated repair of co-stimulation. Eur. J. Immunol. 32 , 2817-2826 (2002). [Abstract] [Full Text]

Suppression of antibody production by TNF-related apoptosis-inducing ligand (TRAIL)

TNF-related apoptosis-inducing ligand (TRAIL), a type II membrane protein belonging to the TNF family, induces apoptotic cell death in various types of tumor cells. However, little is known about its pathological and physiological functions in the immune system. In this study, we showed that administration of neutralizing anti-TRAIL mAb markedly increased serum auto-Ab levels, particularly of IgG1 subclass, in autoimmune-prone C3H/HeJ gld/gld mice without affecting lymphocytosis and lymphocytes populations. In an experimental system where TNP-specific Ab production was induced by immunization with TNP-modified syngeneic B lymphoma cells, expression of TRAIL on these cells significantly reduced TNP-specific Ab production, especially of IgG1 subclass, without affecting T cell priming. These results suggest a new role for TRAIL in the suppression of Ab production.

Influences of anti-mouse interleukin-6 receptor antibody on immune responses in mice

In the present study, we examined the effect of anti-IL-6 receptor antibody (MR16-1) on humoral and cellular immune responses in mice. MR16-1 did not affect antigen-specific antibody production in either the primary or secondary response in mice immunized with dinitro-phenyl (DNP)–keyhole limpet haemocyanin (KLH) in saline. DNP–KLH immunization with complete Freund's adjuvant (CFA) markedly augmented anti-DNP antibody production and induced interleukin 6 (IL-6) production in serum. In this case, MR16-1 significantly suppressed antibody production and further increased serum IL-6 levels. Regarding the cellular response, we studied the effect on the delayed-type hypersensitivity (DTH) response. DTH response was induced in mice by the immunization with Mycobacterium butyricum with incomplete Freund's adjuvant and following antigen challenge into the footpad 14 days after immunization. When MR16-1 was injected immediately after immunization, the DTH response was significantly suppressed and enlargement of the spleen was also suppressed. This suppressive effect was observed, when MR16-1 was administered on day 0, but not on days 5 and 10. Again, serum IL-6 levels were much higher in MR16-1-treated mice compared with controls. Furthermore, spleen cells from control mice released IL-2 and INFγ by the stimulation of antigen in vitro. In contrast, spleen cells from MR16-1-treated mice produced these cytokines at a marginal level. In contrast, MR16-1 did not suppress the DTH response, when it was injected immediately after antigen challenge. Our results suggest that IL-6 does not always involve antibody production, although IL-6 augments antibody production, and that IL-6 is essential for the induction of Th1 cells.

Overcoming immune tolerance during oral vaccination against Actinobacillus pleuropneumoniae.

In the preliminary study mice were vaccinated orally with Actinobacillus pleuropneumoniae microsphere oral vaccine. The lung and eye mucous membranes of these mice did not contain increased immunoglobulin A (IgA) following the initial oral vaccination, possibly through antibody persistence and the phenomenon of immune exclusion. A similar tendency was found for serum IgG. However, after the second vaccination, IgA still did not increase significantly, which could be attributed to immune suppression due to the possibility of the intestine inducing immune tolerance. Only the third vaccination overcame this effect and increased the level of IgA. In order to achieve a high systemic and local immune response this study attempted to overcome the initial tolerance to oral vaccination by using temporary immunosuppression, increasing antigen dose, and prolonging vaccine influence. Triamcinolone, used in the later productive phase of the immune response after the first and second vaccinations, but restricted in the inductive phase of the second and third vaccinations, could disable immune tolerance. Suppression of antibody production before the next induction of the immune response by an oral vaccine combined with suppression of cell-suppressor activity led to the creation of systemic immunity with the possibility of high levels of A. pleuropneumoniae growth inhibition. Increased antigen doses or durable consumption of antigen could overcome immune exclusion of antigen by primary antibodies. Even very low doses of vaccine (4.5 mg) could induce a primary immune response, and a dose increased by 10-fold for the second vaccination could overcome tolerance and maintain high systemic immunity. Chronic consumption of oral vaccine led to benefits in the quantity of local (not systemic) antibodies. The outcomes of the study can be adapted for practical oral immunization of pigs.

Discovery of N-[2-[2-[[3-methoxy-4-(5-oxazolyl)phenyl]amino]-5-oxazolyl]phenyl]-N-methyl-4- morpholineacetamide as a novel and potent inhibitor of inosine monophosphate dehydrogenase with excellent in vivo activity.

Inosine monophosphate dehydrogenase (IMPDH) is a key enzyme that is involved in the de novo synthesis of purine nucleotides. Novel 2-aminooxazoles were synthesized and tested for inhibition of IMPDH catalytic activity. Multiple analogues based on this chemotype were found to inhibit IMPDH with low nanomolar potency. One of the analogues (compound 23) showed excellent in vivo activity in the inhibition of antibody production in mice and in the adjuvant induced arthritis model in rats.

Inhibition of the antibody production by acetaminophen independent of liver injury in mice.

The causal relationship between the inhibition of antibody production and liver injury induced by single doses of acetaminophen (APAP) was investigated in mice. The liver injury and antibody production were evaluated using the serum transaminase activity and the number of antibody forming cells against sheep red blood cells (SRBC), respectively. The relevance of APAP hepatotoxicity with inhibiting antibody production was elucidated in fasted and fed mice treated with a single oral administration of APAP. In fasted mice, the oral administration of APAP produced serious liver injury, while it was not the case in the fed mice. As the antibody production was measured under these conditions, APAP significantly depressed the antibody production in fed mice as well as in fasted mice. The rate of B220 positive cells in the splenocytes was significantly decreased by APAP administration in both the fasted and fed mice. Splenocytes proliferative responses following mitogenic stimulation with concanavalin A or lipopolysaccharide were inhibited by APAP. Moreover, APAP added directly to the splenocyte culture also inhibited the in vitro antibody-producing response to SRBC. These findings indicate that the APAP-induced depression of antibody production may not be a secondary response to APAP-hepatitis, but may be a primary response to APAP.

Identification of a novel receptor for B lymphocyte stimulator that is mutated in a mouse strain with severe B cell deficiency

BLyS (also called BAFF, TALL-1, THANK, and zTNF4), a TNF superfamily member, binds two receptors, TACI and BCMA, and regulates humoral immune responses [1–7]. These two receptors also bind APRIL [7–10], another TNF superfamily member. The results from TACI−/− and BCMA−/− mice suggest the existence of additional receptor(s) for BLyS. The TACI knockout gives the paradoxical result of B cells being hyperresponsive, suggesting an inhibitory role for this receptor [11, 12], while BCMA null mice have no discernable phenotype [13]. Here we report the identification of a third BLyS receptor (BR3; BLyS receptor 3). This receptor is unique in that, in contrast to TACI and BCMA, BR3 only binds BLyS. Treatment of antigen-challenged mice with BR3-Fc inhibited antibody production, indicating an essential role for BLyS, but not APRIL, in this response. A critical role for BR3 in B cell ontogeny is underscored by our data showing that the BR3 gene had been inactivated by a discrete, approximately 4.7 kb gene insertion event that disrupted the 3′ end of the BR3 gene in A/WySnJ mice, which lack peripheral B cells.

Transforming growth factor β enhances the expression of CD154 (CD40L) and production of tumor necrosis factor α by human T lymphocytes

Activation of lymphocytes in the presence of transforming growth factor beta (TGFβ) can impair or enhance their functional activity. We have found that TGFβ is important in the generation of lymphocytes, which are capable of suppressing antibody production. To better understand how this cytokine affects lymphocyte activity, we looked at the expression of early activation events of T cells stimulated in the presence or absence of TGFβ. The results show that TGFβ enhances the expression of CD154 (CD40L), TNFR2 and the production of TNFα. These findings clarify the co-stimulatory effects of TGFβ that enhance T lymphocyte activation.

Steroid Hormones and Immune Function: Experimental Studies in Wild and Captive Dark‐Eyed Juncos (Junco hyemalis)

Monogamous and polygynous male songbirds generally differ in their breeding season profiles of circulating testosterone. Testosterone level spikes early in the breeding season of monogamists and then declines, but it remains high in polygynists. Male dark-eyed juncos (Junco hyemalis) are socially monogamous and exhibit the usual pattern, but experimental maintenance of high testosterone throughout the breeding season alters normal behavior and physiology and affects various components of annual reproductive success but not overall annual success. Because stabilizing selection predicts that alteration of naturally existing phenotypes should reduce lifetime reproductive success, we asked whether prolonged testosterone exposure might impair immune function and perhaps thereby reduce life span. We assessed immune function in captive and wild male juncos that we treated with either testosterone-filled or empty Silastic implants. Results indicate that prolonged elevation of testosterone suppresses antibody production in captive males and cell-mediated immunity in wild males. Together these results suggest that testosterone-treated males may be more susceptible to disease or parasitic infection. As earlier studies have shown, levels of corticosterone as well as testosterone are higher in testosterone-treated males, so it is unclear whether the immune suppression we observed is due to testosterone's direct effects on immunity or testosterone's influence on glucocorticoid production. We discuss results in the context of recent hypotheses regarding life-history theory and potential endocrine-immune interactions.

Antibody-Mediated Immunotoxicity in American Kestrels (Falco sparverius) Exposed to Polychlorinated Biphenyls

Antibody-mediated immune function in adult and recently fledged (30 to 33 d old) American kestrels (Falco sparverius) was examined in birds exposed directly, or only in ovo, to polychlorinated biphenyls (PCBs). In 1998, 9 mature male and 9 female kestrels were fed PCBs, whereas 9 females and 10 males served as controls. A mixture of Aroclors 1248:1254:1260 suspended in safflower oil was injected into the kestrels' food items, while in control diets only the same volume of oil was added. The dosage of PCBs was approximately 7 mg/kg kestrel/d, beginning in March 1998 and continuing for 120 d. In 1998, the antibody-mediated immune response was stimulated by immunization and booster vaccinations of the kestrels using a nonpathogenic antigen, dinitrophenol-keyhole limpet hemocyanin (DNP-KLH). In 1999, offspring from three treatment groups based upon maternal exposure to PCBs were similarly tested for their antibody response. None of these mothers was vaccinated with DNP-KLH the previous year. The maternal groups were: (1) exposed to PCBs in 1998 for 120 d, (2) exposed in ovo in 1998 (i.e., mothers were produced by PCB-exposed parents), or (3) unexposed to PCBs. Serum antibody levels were determined using an enzyme-linked immunosorbent assay (ELISA). In 1998, PCB-exposed adult females had a significantly higher antibody response than did controls, whereas adult males exposed to PCBs had significantly suppressed antibody production. For the nestlings produced in 1999, maternal treatment significantly affected antibody response. Generally, the antibody response in the nestlings was much lower than that seen in adult kestrels. Yet both male and female offspring from mothers that had been fed PCBs the previous year had significantly higher postbooster anti-DNP-KLH titers than control and in ovo-exposed maternal groups, thus mimicking the response seen in the adult females the previous year. These sex-specific responses in PCB-exposed birds provide further evidence of the endocrine-disrupting behavior of PCBs. Both suppression and stimulation of the antibody response are undesirable because this indicates that the immune system is not able to respond normally to challenges by infectious or other disease-causing agents.

Specificity, restriction and effector mechanisms of immunoregulatory CD8 T cells

Historically, CD8 T cells have been divided into cytotoxic T cells and suppressor T cells. Cytotoxic CD8 T cells have been regarded as a homogeneous population of CD4-dependent cells producing a limited number of cytokines – namely interferon (IFN-γ), tumour necrosis factor (TNF-α) and lymphotoxin. Their function was thought to be restricted to defence against viral infections and intracellular pathogens. CD8 suppressor T cells were considered a functionally distinct population of CD8 T cells, which switch off established immune responses or maintain tolerance to particular antigens.1–4 The idea of suppressor T cells first arose in the late 60s and early 70s, when early work of Gershon and colleagues showed that adoptive transfer of T cells from animals tolerant to a particular antigen could specifically suppress antibody production (against that particular antigen) in the recipient animals.5,6 The advances in immunology during the 1970s led to the idea that distinct T cell functions were mediated by distinct subsets of T cells, expressing different cell surface molecules. These findings were further extended to other species, and it was subsequently proposed that cytotoxic and suppressor populations belonged to the CD8 T-cell subset.7–10 In the early studies in both mice and human models suppression was shown to require interaction between CD8 and CD4 T cells. It was proposed that activated CD4 T cells were required for the induction of the CD8 suppressor cells11,12 which then mediate suppression by inhibiting functions of the inducing CD4 T-cell population. These experiments led to models in which very complex cellular circuits were proposed13–16 involving a confusing array of suppressor cells, factors and mechanisms. To this day the existence of these putative antigen (Ag)-specific suppressive factors has not been resolved leading to widespread dismissal of the existence of suppressor cells.17 However, CD8 T-cell-mediated suppression has been clearly demonstrated in a number of systems including: antibody responses to soluble and cellular antigens,18–20 responses to superantigens,21,22 graft-versus-host disease (GVHD),23 allograft rejection,24 asthma (virus induced)25 and in oral tolerance.26,27 More recently, a number of groups have demonstrated that human, murine and rat CD8 T cells have the potential to produce a much wider array of cytokines than was initially thought. Moreover, CD8 T cells appear to differentiate in a polarized fashion and can be divided into subsets analogous to those described for CD4 T cells. These subsets were termed type 1 or Tc1 and type 2 or Tc2.28,29 However, while in the CD4 cells, different cytokine profiles were closely associated with specific functions, i.e. T helper type 1 (Th1) cells were inflammatory T cells, while T helper type 2 (Th2) cells were helpers for antibody production, a correlation between cytokine profile and function has yet to be clearly defined for CD8 T cells. Furthermore it is difficult to associate the newly described CD8 T-cell subsets with phenomena of immune suppression. However, as some CD8 T cells produce potent immunoregulatory cytokines such as interleukin-4 (IL-4),30 IL-1031 and transforming growth factor-β (TGF-β),32 it is likely they may play a role in immune regulation including suppression. In addition, more and more evidence has emerged indicating that CD8 T cells have the capacity to regulate both the induction and effector phases of the immune response through their secreted products or through direct interaction with other cells. Here, we review evidence, old and new, for the capacity of CD8 T cells to influence the outcome of numerous immune responses.