Mechanisms Of Unresponsiveness Research Articles

WWP1 inactivation enhances efficacy of PI3K inhibitors while suppressing their toxicities in breast cancer models

Activation of the phosphatidylinositol 3-kinase (PI3K) signaling pathway is a pervasive event in tumorigenesis due to PI3K mutation and dysfunction of phosphatase and tensin homolog deleted on chromosome 10 (PTEN). Pharmacological inhibition of PI3K has resulted in variable clinical outcomes, however, raising questions regarding the possible mechanisms of unresponsiveness and resistance to treatment. WWP1 is an oncogenic HECT-type ubiquitin E3 ligase frequently amplified and mutated in multiple cancers, as well as in the germ lines of patients predisposed to cancer, and was recently found to activate PI3K signaling through PTEN inactivation. Here, we demonstrate that PTEN dissociated from the plasma membrane upon treatment with PI3K inhibitors through WWP1 activation, whereas WWP1 genetic or pharmacological inhibition restored PTEN membrane localization, synergizing with PI3K inhibitors to suppress tumor growth both in vitro and in vivo. Furthermore, we demonstrate that WWP1 inhibition attenuated hyperglycemia and the consequent insulin feedback, which is a major tumor-promoting side effect of PI3K inhibitors. Mechanistically, we found that AMPKα2 was ubiquitinated and, in turn, inhibited in its activatory phosphorylation by WWP1, whereas WWP1 inhibition facilitated AMPKα2 activity in the muscle to compensate for the reduction in glucose uptake observed upon PI3K inhibition. Thus, our identification of the cell-autonomous and systemic roles of WWP1 inhibition expands the therapeutic potential of PI3K inhibitors and reveals new avenues of combination cancer therapy.

Overcoming rituximab drug-resistance by the genetically engineered anti-CD20-hIFN-α fusion protein: Direct cytotoxicity and synergy with chemotherapy.

Treatment of patients with B-NHL with rituximab and CHOP has resulted in significant clinical responses. However, a subset of patients develops resistance to further treatments. The mechanism of unresponsiveness in vivo is not known. We have reported the development of rituximab-resistant clones derived from B-NHL cell lines as models to investigate the mechanism of resistance. The resistant clones exhibit hyper-activated survival/anti-apoptotic pathways and no longer respond to a combination of rituximab and drugs. Recent studies reported the therapeutic efficacy in mice bearing B-cell lymphoma xenografts following treatment with the anti-CD20-hIFNα fusion protein. We hypothesized that the fusion protein may bypass rituximab resistance and inhibit survival signaling pathways. Treatment of the rituximab-resistant clones with anti-CD20-hIFNα, but not with rituximab, IFNα, or rituximab+IFNα resulted in significant inhibition of cell proliferation and induction of cell death. Treatment with anti-CD20-hIFNα sensitized the cells to apoptosis by CDDP, doxorubicin and Treanda. Treatment with anti-CD20-hIFNα inhibited the NF-κB and p38 MAPK activities and induced the activation of PKC-δ and Stat-1. These effects were corroborated by the use of the inhibitors SB203580 (p38 MAPK) and Rottlerin (PKC-δ). Treatment with SB203580 enhanced the sensitization of the resistant clone by anti-CD20-hIFNα to CDDP apoptosis. In contrast, treatment with Rotterin inhibited significantly the sensitization induced by anti-CD20-hIFNα. Overall, the findings demonstrate that treatment with anti-CD20-hIFNα reverses resistance of B-NHL. These findings suggest the potential application of anti-CD20-hIFNα in combination with drugs in patients unresponsive to rituximab-containing regimens.

Abstract SF1-2: Improving access to innovative anticancer medicines: a clinicians viewpoint

Abstract For most forms of cancer there is high unmet need. This is especially the case for advanced cancer. Improved understanding of mechanisms of unresponsiveness to currently available treatments and identification of novel drugable targets have boosted anticancer drug development, often leading to so-called breakthrough medicines, i.e. drugs that can dramatically improve cure rate and survival. The monoclonal antibodies (mAb) trastuzumab and rituximab and the tyrosine kinase inhibitor (TKI) imatinib, developed in the recent past, deserved this qualification. These drugs have not only changed the standard of practice, they also served as template for new drug development leading to EMA & FDA approval of >30 novel mAbs and TKIs for cancer indications since the introduction of rituximab in 1998. However, this does not guarantee swift patient access to new medicines nor to equal access for all indicated patients. Also, some drugs with high anticancer potential in well defined cancer populations simply seem to be stuck in development. One of the examples of missed opportunities is the group of the PARP inhibitors (PARPi): first patient included in phase I was in the year 2005 and now almost a decade later there is still no availability worldwide for well characterized populations with BRCAm, including breast and ovarian cancer, of PARPi treatment. Clearly, there is room for improvement, for which there is a range of good opportunities: shorten time to registration, shorten time to reimbursement, improve patient selection, limit to well defined subsets and expand later, setup global biomarker networks, setup global well controlled access programs and lastly take more risk. These opportunities will be discussed and examples will be given. Citation Format: Jan H. M. Schellens. Improving access to innovative anticancer medicines: a clinicians viewpoint [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr SF1-2.

Detection of AmpC-β lactamase Enzymes by AmpC DiscTest

Microbes have many mechanisms of unresponsiveness to antimicrobial agents that may arise in them over months or years. Among them degradation of antibiotics by enzymes is one of the common methods of bacterial resistance particularly in Enterobacteriacea.1,2 At least 400 different types of β-lactamases from clinical isolates have been discovered. Broadly they are of three types: extended spectrum beta lactamases (ESBLs), Amp C β-lactamases and carbapenemases. AmpC type beta lactamases are cephalosporinases and hydrolyze penicillins, cephalosporins, except the fourth-generation compounds and monobactams.3,4,5 JMS 2014;17(2):74-75

Specific messenger RNA expression for signal transduction molecules by lipopolysaccharide in intestinal macrophages

Intestinal macrophages are known to display profound inflammatory anergy in response to lipopolysacchraide (LPS). To study the mechanisms of unresponsiveness of intestinal macrophages to LPS, we compared the mRNA expression of molecules associated with signal transduction of intestinal macrophages with those of other tissue macrophages. Also cellular localization of CD14 protein was examined. Intestinal, alveolar and peritoneal macrophages were isolated from rats or mice. The expression of mRNA was assessed by real-time PCR, and cellular localization of CD14 protein was examined by flow cytometry. Cellular responses to LPS were examined by production of TNF and NO. The expression of CD14 mRNA in intestinal macrophages was lower than for peritoneal macrophages but higher than for alveolar macrophages. The mRNA expression of other molecules corresponding to intracellular signal transduction in intestinal macrophages was similar with alveolar and peritoneal macrophages. Despite the presence of CD14 mRNA, proteins of CD14 were not detected on cell surfaces of intestinal macrophages, and induction of TNF or NO responding to LPS were not detected. Flow cytometric analysis demonstrated that CD14 protein was not expressed on the cell surface but was expressed inside intestinal macrophages. The unresponsiveness of intestinal macrophages after LPS exposure is considered to be largely attributed to the lack of CD14 protein on their cell surfaces. However, CD14 protein was expressed inside of the cells, suggesting that post-transcriptional regulation rather than transcriptional suppression may play a dominant role in determining the phenotype of the intestinal macrophages.

Plasma membrane sequestration of apoptotic protease-activating factor-1 in human B-lymphoma cells: a novel mechanism of chemoresistance

AbstractBurkitt lymphoma (BL) is a highly aggressive B-cell neoplasm harboring chromosomal rearrangements of the c-myc oncogene. BL cells frequently resist apoptosis induction by chemotherapeutic agents; however, the mechanism of unresponsiveness has not been elucidated. Here, we show that cytochrome c fails to stimulate apoptosome formation and caspase activation in cytosolic extracts of human BL-derived cell lines, due to insufficient levels of apoptotic protease-activating factor-1 (Apaf-1). Enforced expression of Apaf-1 increased its concentration in the cytosolic compartment, restored cytochrome c-dependent caspase activation, and rendered the prototypic Raji BL cell line sensitive to etoposide- and staurosporine-induced apoptosis. Surprisingly, in nontransfected BL cells, the bulk of Apaf-1 was found to associate with discrete domains in the plasma membrane. Disruption of lipid raft domains or the actin cytoskeleton of Raji cells liberated Apaf-1 and restored sensitivity to cytochrome c–dependent apoptosis, indicating that constitutive Apaf-1 retained its ability to promote caspase activation. Moreover, disruption of lipid rafts sensitized BL cells to apoptosis induced by etoposide. Together, our findings suggest that ectopic (noncytosolic) localization of Apaf-1 may constitute a novel mechanism of chemoresistance in B lymphoma.

Cellular and molecular signal transduction pathways modulated by rituximab (rituxan, anti-CD20 mAb) in non-Hodgkin's lymphoma: implications in chemosensitization and therapeutic intervention

The clinical application of rituximab (chimeric mouse anti-human CD20 mAb, Rituxan, IDEC-C2B8), alone and/or combined with chemotherapy, has significantly ameliorated the treatment outcome of patients with relapsed and refractory low-grade or follicular non-Hodgkin's lymphoma (NHL). The exact in vivo mechanisms of action of rituximab are not fully understood, although antibody-dependent cell-mediated cytotoxicity (ADCC), complement-dependent cytotoxicity (CDC), and apoptosis have been suggested. We have proposed that modifications of the cellular signaling pathways by rituximab may be crucial for its clinical response. The B-cell restricted cell surface phosphoprotein CD20 is involved in many cellular signaling events including proliferation, activation, differentiation, and apoptosis upon crosslinking. Monomeric rituximab chemosensitizes drug-resistant NHL cells via selective downregulation of antiapoptotic factors through the type II mitochondrial apoptotic pathway. Several signaling pathways are affected by rituximab which are implicated in the underlying molecular mechanisms of chemosensitization. ARL (acquired immunodeficiency syndrome (AIDS)-related lymphoma) and non-ARL cell lines have been examined as in vitro model systems. In ARL, rituximab diminishes the activity of the p38MAPK signaling pathway resulting in inhibition of the interleukin (IL)-10/IL-10R autocrine/paracrine cytokine autoregulatory loop leading to the inhibition of constitutive STAT-3 activity and subsequent downregulation of Bcl-2 expression leading to chemosensitization. Rituximab upregulates Raf-1 kinase inhibitor protein (RKIP) expression in non-ARL cells. Through physical association with Raf-1 and nuclear factor kappaB (NF-kappa B)-inducing kinase (NIK), RKIP negatively regulates two major survival pathways, namely, the extracellular signal-regulated kinase1/2 (ERK1/2) and the NF-kappa B pathways, respectively. Downmodulation of the ERK1/2 and NF-kappa B pathways inhibits the transcriptional activity of AP-1 and NF-kappa B transcription factors, respectively, both of which lead to the downregulation of Bcl-(xL) (Bcl-2 related gene (long alternatively spliced variant of Bcl-x gene)) transcription and expression and sensitization to drug-induced apoptosis. Bcl-(xL)-overexpressing cells corroborated the pivotal role of Bcl-(xL) in chemosensitization. The specificity of rituximab-mediated signaling and functional effects were corroborated by the use of specific pharmacological inhibitors. Many patients do not respond and/or relapse and the mechanisms of unresponsiveness are unknown. Rituximab-resistant B-NHL clones were generated to investigate the acquired resistance to rituximab-mediated signaling, and chemosensitization. Resistant clones display different phenotypic, genetic and functional properties compared to wild-type cells. This review summarizes the data highlighting a novel role of rituximab as a signal-inducing antibody and as a chemosensitizing agent through negative regulation of major survival pathways. Studies presented herein also reveal several intracellular targets modified by rituximab, which can be exploited for therapeutic and prognostic purposes in the treatment of patients with rituximab- and drug-refractory NHL.

Rituximab-mediated chemosensitization of AIDS and non-AIDS non-Hodgkin's Lymphoma

Patients with B non-Hodgkin's Lymphoma (NHL) initially respond to conventional chemotherapy. However, relapses and recurrences occur and the patients develop resistance to further treatment. Immunotherapeutic approaches have been considered in the treatment of such patients. Rituximab (chimeric anti-human CD20 monoclonal antibody) is the first anti-cancer monoclonal antibody approved by the FDA for the treatment of B-NHL. It has been used alone or in combination with chemotherapy, and the clinical response rates have been 50% and greater than 95%, respectively. The in vivo mechanism by which rituximab mediates its effects is not clear, though ADCC, CDC and apoptosis have been suggested and supported by several studies. However, many patients do not respond to rituximab or become refractory to rituximab treatment and the underlying mechanism of unresponsiveness is not known. This review describes various molecular signaling pathways modified by rituximab using in vitro B-NHL cell lines as model systems. The findings demonstrate that rituximab treatment modulates the p38 MAPK, the Raf-1/MEK/ERK1/2 and the NF-kappaB pathways. These modifications induced by rituximab were in large part responsible for the down-regulation of the anti-apoptotic gene products Bcl-2/Bcl-xL and chemosensitization of the drug-resistant B-NHL cell lines to various drug-induced apoptosis. Studies on the development of resistance to rituximab were investigated with rituximab-resistant B-NHL clones derived from rituximab-sensitive B-NHL cell lines. The molecular signaling pathways modified by rituximab revealed several novel intracellular targets whose modification could sensitize both rituximab-sensitive and rituximab-resistant B-NHL to drug-induced apoptosis. These in vitro findings provide new possibilities for improving the clinical effectiveness of rituximab as well as for circumventing its resistance.

Alloantigen-induced specific immunological unresponsiveness.

When the immune system encounters alloantigen it can respond in any one of a number of different ways. The choice that is made will take into account factors such as where, when and how the contact with the alloantigen takes place, as well as the environmental conditions that prevail at the time the alloantigen is encountered. Alloantigen administration before transplantation either alone or in combination with therapeutic agents that modulate the functional activity of the responding leucocytes can be a powerful way of inducing specific unresponsiveness to alloantigens in vivo. The molecular mechanisms that influence the way the outcome of the immune response to alloantigen develops, either activation or unresponsiveness to the triggering antigen, hold the key to our ability to manipulate the immune system effectively by exposing it to donor antigen for therapeutic purposes. This review will focus on alloantigen-induced immunological unresponsiveness and how insights into the mechanisms of unresponsiveness have driven the development of novel tolerance-induction strategies that show promise for translation into the clinic in the future.

Mechanisms of unresponsiveness: T- and B-cell mediated mechanisms of anergy.

In this chapter we will attempt to briefly review the relevant immunological concepts concerning both T and B cell unresponsiveness. We will focus on the broad concepts, and use them to frame the problems of gene therapy related to hemophilia.KeywordsMajor Histocompatibility ComplexGene TherapyFactor VIIIHemophilia PatientPeripheral Immune SystemThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Stimulation of tumour necrosis factor-alpha production by recombinant human erythropoietin may contribute to failure of therapy.

Although the mechanism of unresponsiveness to recombinant human erythropoietin therapy in dialysis patients has been studied extensively in recent years, many aspects remain unclear. We previously found that administration of erythropoietin induces interleukin-1beta, a cytokine that inhibits erythropoiesis. The present study investigated the involvement of tumour necrosis factor-alpha, another cytokine which inhibits erythropoiesis. Peripheral blood mononuclear cells were obtained from 18 patients on continuous ambulatory peritoneal dialysis, who were being treated with erythropoietin for renal anaemia, and were cultured with various concentrations of erythropoietin (0, 1, 5, 10, and 50 U/ml). Then the tumour necrosis factor-alpha level in the culture supernatant was assayed. The 18 patients were divided into four groups on the basis of the haematocrit after treatment: group A (n = 3), <23.0%; group B (n = 5), 23.0-24.9%; group C (n = 7), 25.0-26.9%; and group D (n = 3), > or =27.0%. In group A, the tumour necrosis factor-alpha level in the culture supernatant was increased by incubation with erythropoietin, while it was not increased in other groups. The tumour necrosis factor-alpha level was significantly higher in group A than in the other groups at erythropoietin concentrations of 5 U/ml. These results suggested that induction of tumour necrosis factor-alpha is one of the reasons for unresponsiveness to recombinant human erythropoietin.

Mechanisms of unresponsiveness to alloantigens in vivo

Mechanisms of unresponsiveness to alloantigens in vivo

Stimulation of Interleukin-1 ß Production may be Involved in Unresponsiveness to Erythropoietin Therapy

Recombinant human erythropoietin (rHuEPO) can dramatically improve anemia in dialysis patients, but about 20% of patients show a poor response to this agent. It has been reported that cytokines, including interleukin (IL)-1 beta, may inhibit the maturation of erythrocytes. To investigate the mechanisms of unresponsiveness to rHuEPO, we isolated peripheral blood mononuclear cells from 12 patients on continuous ambulatory peritoneal dialysis who were receiving maintenance rHuEPO therapy for renal anemia. Cells were cultured with rHuEPO and IL-1 beta production was assessed. In the six patients who did not respond to rHuEPO therapy, there was a marked increase in IL-1 beta during culture with rHuEPO. In contrast, the addition of rHuEPO to cultures of cells from the six responding patients caused little increase in IL-1 beta, and there was a significant difference between the two groups. Induction of IL-1 beta by rHuEPO may be one cause of persistent anemia in dialysis patients.

Mechanisms of unresponsiveness to heart allograft induced by intra thymic inoculation of alloantigen in the rat

Mechanisms of unresponsiveness to heart allograft induced by intra thymic inoculation of alloantigen in the rat

Mechanisms of unresponsiveness associated with pretransplant blood transfusion-cyclosporine-induced mixed lymphocyte chimerism.

Multiple pretransplant blood transfusions while under limited daily cyclosporine cover (PTBT-CsA) induce extensive rat renal allograft survival and antigen-specific non-responsiveness. The underlying mechanisms of this extensive allograft survival are not yet fully understood. We hypothesized that one of the potential contributing mechanisms to tolerance induction in PTBT-CsA-treated kidney recipients is the development of stable mixed chimerism, putatively due to the proliferation of stem cells capable of haematopoiesis in the transfused blood. BN rats served as whole blood and kidney donors. LEW rats served as recipients of the PTBT-CsA protocol and BN kidney transplants. Three weekly transfusions were given under concomitant limited CsA cover. Following these multiple primary sensitizations, antigen-specific splenic cellular responsiveness in vivo was normal in comparison with naive animals. However, these experimental splenocytes were non-specifically suppressed against third-party allodeterminants. At 100 days post-transplantation (T100) following tolerance induction to kidney allografts (secondary challenge), in vivo adoptive transfer experiments demonstrated the existence of potent splenic suppressor cells. In vitro suppressor cell assays confirmed that these cells were non-specific suppressor cells. However, following chimerism stabilization at T130, splenic antigen-specific suppressor cells became exclusively expressed in the tolerant animals, replacing the non-specific suppressor cells. At this time, splenic microchimerism was at peak levels and remained stable from T100 to T130. In conclusion, these findings demonstrate that sequential mechanisms of suppressor cell network expression are induced within a chimeric environment by blood-CsA immune modulation. Stable mixed lymphocyte chimerism and related immunomodulatory mechanisms may, therefore, play an important tolerogenic role in blood-CsA-induced non-responsiveness and in the beneficial effect of blood transfusion.

Organ-specific unresponsiveness induced by intrathymic injection of donor bone marrow cells and a short course of immunosuppression in the rat heart transplantation model

Donor- and organ-specific unresponsiveness to Brown Norway (BN) heart allografts was achieved in Lewis (LEW) rats by giving intrathymic donor bone marrow cells (ITBMC) and immunosuppression at the time of transplantation. Antilymphocyte serum (ALS) (1 mlo, days 0,2,4) extended graft survial to a median survival time (MST) of 29.5 days ( n = 6), while ALS + ITBMC extended survival to over 120 days ( n = 6). FK506 (1 MG/KG, DAYS 0,2,4,6,8) too prolonged survival in the FK + ITBMC ( n = 6 MST > 140 days) and FK ( n = 5; MST > 140 days) groups. BN skin grafting provoked the rejection of long-surviving BN heart grafts in the FK group ( n = 5; MST = 14 days), but did not do so in either the ALS + ITBMC ( n = 2; MST > 100 days) or the FK + ITBMC ( n = 4; MST > 93 days) groups. In the FK + ITBMC group, two of the rats which rejected BN skin grafts received a second BN heart, resulting in the graft being accepted indefinitely (> 100 days) without causing the rejection of the first BN heart grafts. These facts suggest that ITBMC and concurrent T cell depletion are decisive for induction of unresponsiveness by this protocol. BN and WF (Wistar Furth) skin grafts were eventually rejected in the LEW rats which accepted BN heart grafts. Persistent allogeneic chimerism was demonstrated in the graft and recipient spleen, suggesting that chimerism may be one of the possible mechanisms of unresponsiveness. The procedure reported here deserves further evaluation, but appears to be a possible clinical strategy for the induction of unresponsiveness.

THE ROLE OF T SUPPRESSOR CELLS IN THE MAINTENANCE OF SPONTANEOUSLY ACCEPTED ORTHOTOPIC RAT LIVER ALLOGRAFTS

Orthotopic liver allografts from BN donors to LEW recipients are spontaneously accepted, and the recipients develop donor-specific immunological unresponsiveness. This unresponsiveness may be mediated by suppressor T cells. Immunomagnetically purified splenic T cells from LEW rats bearing BN liver grafts were shown to adoptively transfer suppression of skin, heart, and kidney graft rejection in a donor-specific manner, prolonging the survival of BN but not third-party DA grafts. However, the suppressor T cells were sessile, being resident in the spleen but not present in thoracic duct lymph. The presence of a nonrecirculating suppressor T cell in rats spontaneously accepting liver transplants is strongly suggestive of an important function in the maintenance of donor-specific unresponsiveness, although the contribution of other possible mechanisms of unresponsiveness has not been investigated.

SOLUBLE ANTIGEN AND CYCLOSPORINE-INDUCED SPECIFIC UNRESPONSIVENESS IN RATS

The cellular mechanisms of unresponsiveness induced with a combined KCl-extracted donor antigen (HAg) and CsA regimen were dissected by limiting-dilution (LD) assay. While untreated Wistar-Furth (WFu, RT1u) rats reject Buffalo (BUF, RT1b) heart allografts within a mean survival time of 6.6 +/- 0.5 days, recipients treated with 3 cycles of CsA alone (-1,0,1; 7,8,9; 15,16,17) maintained BUF heart allografts up to an MST of 22.5 +/- 8.9 days. When CsA was combined with BUF HAg (-1), BUF heart survival was further prolonged up to an MST of 34.2 +/- 6.6 days, while third-party BN HAg was ineffective (MST of 21.5 +/- 2.1 days). On day 10 postgrafting, the frequency of T cytotoxic cells (fTc) within the splenic pan-T-cell population was 1:1437 +/- 301 in CsA and 1:1087 +/- 438 in CsA/HAg treated recipients. In contrast, on day 30 postgrafting, both CsA and CsA/HAg treated WFu rats bearing functional BUF hearts showed within their splenic pan-T-cell populations a profound decrease in fTc to 1:2966 +/- 824 with CsA alone and to 1:4946 +/- 938 with CsA/HAg treatment. In contrast, both untreated WFu rats who rejected BUF heart allografts and CsA-treated WFu recipients who had rejected their BUF heart allografts on day 20 displayed an increased fTc to 696 +/- 243 and to 1:1169, respectively, when examined at day 30 postgrafting. Additionally, both the W3/25+ and OX8+ T cell subsets specifically suppressed the proliferative response of normal WFu T cells against BUF and, to a lesser degree, third-party BN irradiated stimulators. Thus, CsA-treated animals develop a potent specific-suppressor mechanism that is augmented by pretreatment with donor soluble antigen. This suppressor activity may decrease the frequency of alloantigen-specific Tc cells and thereby prolong the survival of BUF heart allografts.

Patterns of bovine T cell-mediated immune responses to bovine herpesvirus 1

Lymphocyte proliferation was used to evaluate T cell-mediated immune responses to different isolates of Bovine Herpesvirus 1 (BHV-1). Groups of high, moderate, and low responses were observed when lymphocytes from three breeds of dairy cattle were stimulated with each of the BHV-1 isolates. Proliferation of cells in the low responding group could be augmented by exogenous IL-2. The mechanism of unresponsiveness by cells from one individual whose response was not altered by IL-2 supplementation was further investigated. The patterns of response by limiting dilution frequency analysis eliminated the possibility that this individual lacked responsive cells but suggested the presence of regulatory cell interactions which resulted in the observed low proliferative response. These results show that animals exposed to the same environment can vary greatly in their ability to respond to BHV-1. At least two mechanisms may be responsible for low proliferative responses in vitro : inadequate levels of IL-2 and the presence of suppressor cells.

Tolerance to the trinitrophenol ligand in guinea pigs: studies on the role of the solvent used in feeding.

Guinea pigs fed picryl sulfonic acid in aqueous solvents did not become unresponsive to contact sensitization with picryl chloride. In contrast, a substantial proportion of those fed picryl sulfonic acid, emulsified with triglyceride oil, were tolerant to subsequent immunization with picryl chloride. Feeding a related hapten (picryl chloride) in aqueous solvents was also considerably less effective in the induction of unresponsiveness to contact sensitization than feeding this hapten in vegetable oil. Animals fed picryl sulfonic acid in either aqueous or emulsified triglyceride solvents developed picryl-specific antibody after the initial feeding. However, those fed picryl chloride did not develop antibody and its role, if any, in the mechanism of unresponsiveness is unclear.