Search

Polyelectrolyte multilayer adsorption on mica was studied by the streaming potential method in the parallel-plate channel setup. The technique was calibrated by performing model measurements of streaming potential by using monodisperse latex particles. Two types of polyelectrolytes were used in our studies:  poly(allylamine) hydrochloride (PAH), of a cationic type, and poly(sodium 4-styrenesulfonate) (PSS) of an anionic type, both having molecular weight of 70 000. The bulk characteristics of polymers were determined by measuring the specific density, diffusion coefficient for various ionic strengths, and zeta potential. These measurements as well as molecular dynamic simulations of chain shape and configurations suggested that the molecules assume an extended, wormlike shape in the bulk. Accordingly, the diffusion coefficient was interpreted in terms of a simple hydrodynamic model pertinent to flexible rods. These data allowed a proper interpretation of polyelectrolyte multilayer adsorption from NaCl solutions of various concentrations or from 10^-3 M Tris buffer. After completing a bilayer, periodic variations in the apparent zeta potential between positive and negative values were observed for multilayers terminated by PAH and PSS, respectively. These limiting zeta potential values correlated quite well with the zeta potential of the polymers in the bulk. The stability of polyelectrolyte films against prolonged washing (reaching 26 h) also was determined using the streaming potential method. It was demonstrated that the PSS layer was considerably more resistant to washing, compared to the PAH layer. It was concluded that the experimental data were consistent with the model postulating particle-like adsorption of polyelectrolytes with little chain interpenetration. It also was concluded that due to high sensitivity, the electrokinetic method applied can be effectively used for quantitative studies of polyelectrolyte adsorption, desorption, and reconformation.

Objective: This study addressed the role of the pattern recognition receptors (PRR), which recognize different molecular structures present on microorganisms, apoptotic, senescent and tumor cells, in the stimulation of human monocyte and monocyte-derived macrophages (MDM) for the production of intracellular cytokines. Materials and methods: Monocytes and MDM were stimulated with different ligands of scavenger receptors (SR) and mannose receptor (MR). Production of intracellular cytokines: tumor necrosis factor alpha (TNFa), interleukin 10 and 12 (IL-10, IL-12) was determined by flow cytometry following staining with anti-cytokine monoclonal antibodies (mAbs). Results: The ligands of SR type A: fucoidan, polyguanylic acid (polyG), chemically modified low density lipoproteins (LDL), ligands of SR-B: native and chemically modified LDL, and ligand of mannose receptor (MR) – mannan induced strong expression of intracellular TNFa and weaker IL-10 in monocytes, while phosphatidylserine (PdS) was without effect. IL-12 was stimulated only by fucoidan and polyG. The induction of cytokine m-RNA generally followed the pattern and the magnitude of intracellular cytokine production. In MDM, intracellular TNFa and IL-12 expression was induced by mannan, native and modified LDL, but not other ligands. Expression of IL-10 was less pronounced and occurred following stimulation with fucoidan, polyG and modified, but not native, LDL. Conclusions: These results suggest that some PRR ligands may be involved in activation of monocytes/MDM for the production of mainly proinflammatory cytokines (TNFa, IL-12) implicating their role in the response to microbial and tumor invasion.

The assessment of intracellular cytokines at the single-cell level by flow cytometry has recently become a potent tool in many areas of cell biology and in defining the role of cytokines in various human diseases. Three-color flow cytometry for detection of intracellular cytokines combined with simultaneous determination of lymphocytes (CD3(+) and CD4(+)) or monocytes (CD33(+) and CD14(+)) was used for comparison of phytohemagglutinin (PHA)-and phorbol myristate acetate (PMA)-ionomycin-induced production of intracellular cytokines in peripheral blood mononuclear cells (PBMCs) of healthy donors. We found that the number of PBMCs stained for tumor necrosis factor alpha and gamma interferon after 6 h of activation was higher when PMA-ionomycin was used for stimulation, while the frequencies of cells positive for interleukin 4 (IL-4) were similar for both stimulators. However, PMA-ionomycin stimulation caused prominent alterations of cell morphology and membrane expression of CD4 and CD14. In contrast, PHA did not cause downregulation of surface markers and resulted in less pronounced alterations in both forward and side scatter signals during flow cytometry analysis. Moreover, during 48 h of culture PHA stimulated tumor necrosis factor beta and IL-10 production, which was not observed when PMA-ionomycin was used. We conclude that the use of PHA for cell activation may limit in vitro artifacts and allow more precise analysis of intracellular cytokine production in various disease states.

The zeta potentials of natural mica, bare and covered by positively charged latex particles of micrometer size range, were determined by the streaming potential method. Measurements were carried out using the parallel-plate channel formed by clamping together two mica sheets separated by a Teflon spacer. The dependence of streaming potential on surface coverage (Θ) of adsorbed particles was determined for various ionic strengths and particle sizes. The coverage was determined directly by optical and electron microscope counting procedures. It was found that the negative streaming potential for bare mica Es was significantly increased by the presence of adsorbed particles. The dependence of the reduced streaming potential Esp/Es (where Esp is the zeta potential in the presence of particles) on Θ exhibited an universal behavior being independent of particle size and ionic strength. These experimental data were interpreted in terms of a theoretical model postulating that the streaming potential change was due to flow damping over the interface and by charge transport from the double-layer surrounding adsorbed particles. In contrast with previous approaches no assumption of the slip (shear) plane shift upon particle adsorption was made. By exploiting the experimental results it was suggested that colloid and bioparticle adsorption kinetics can be studied in situ using the streaming potential method.

The pressure in the Reverse Wilson Chamber (RWC) was directly measured at different rates of compression of the gas mixture. It was shown that at compression time Τ in the range from 0.06 to 0.3 s an intermediate, between adiabatic and isothermal, process took place in the chamber. To obtain the relative pressure increaseδ Pm/Patfrom the values of the relative gas compressionδ V/V, a calibration of the experimental set-up was carried out. The calibration showed that the values of critical supersaturationScfor water condensation on hexadecane, estimated for intermediate regime of the gas compression, were reduced with respect to the values calculated when the adiabatic regime was assumed. This fact confirmed the conclusions made earlier [1–3] that the classical theory was not applicable in this case of heterogeneous phase formation and that the line tensionκ< 0 should be taken into account. Moreover, in an atmosphere of very pure argon (instead of room air [1–3]) the critical supersaturation turned out to be independent of the initial state of undersaturationSo. The more accurate values obtained for condensation of water on hexadecane were: lnSc=0.204 (instead of the maximum value obtained earlier: lnSc=0.26) andκ=−1.9×10−5dyne (instead ofκ=−1.5×10−5dyne).

Recurrent and severe infections and absence of thymic shadow in X-ray examination were observed in children with the transposition of the great arteries (TGA). Among 45 children (29 boys and 16 girls) with TGA whose age ranged from 3 days to 16 years and who were hospitalized during 1 year, infectious diarrhea was observed in 77.7% cases, urinary tract infections in 44.5%, respiratory tract infections in 42.2%, sepsis in 17.5%, and meningitis in 8.8%. Nine of the children died, sepsis was a cause of death in seven children, and there were postsurgical complications in two children. Immunologic abnormalities in children with TGA included a decreased level of T-lymphocytes and T29° subpopulation, impaired mitogen-induced lymphoproliferation in vitro, and increased nitro blue tetrazolium (NBT) reduction activity of monocytes. Impaired parameters of cellular immunity correlated with worst clinical status. No disorders of humoral immunity were observed. These observations may be important for forming opinion about proper therapy and the cause of death in children with TGA.

Monocytes are eliminated from cell culture by antigen or mitogen activated cytotoxic CD4+ T-lymphocytes. In this report we asked the question whether CD4+CD45RA+ and CD4+CD45RO+ subpopulations differ in the ability to kill monocytes in pokeweed mitogen (PWM)-activated cultures. Data are presented that although CD4+CD45RA+ vigorously proliferate in the presence of PWM, they do not kill monocytes or secrete IFNγ.

Stable unsymmetrical liquid films in the mercury-aqueous dodecyltriethylammonium perchlorate (DTEAClO4) solutions-air system were formed. Under similar experimental conditions, in the case of DTEACl, the films ruptured within 20 sec. Electrochemical studies of the mercury electrode in DTEAClO4and DTEACl solutions suggest that strong lateral interactions between adsorbed ions occur for DTEAClO4.

The elution of proteins from various surfaces by surfactants was widely studied in the literature in connection with practical applications but also as a tool to understand protein adsorption behavior. In this paper we present the results obtained for the following system:  fibrinogen adsorbed at a silica surface eluted by sodium dodecyl sulfate (SDS) solutions of various concentrations and at various ionic strengths. The process was followed by measuring the radioactivity of labeled protein. The elution kinetics was determined and described quantitatively by an apparent rate constant k and an elutability parameter. An unexpected nonmonotonic dependence of k as a function of SDS concentration cSDS was obtained for the first time. This nonmonotonic behavior of k was explained assuming double action of SDS molecules on the fibrinogen adsorption layer:  SDS with its detergent ability removes adsorbed protein but, being at the same time a strong denaturing agent, it is able to transform adsorbed molecules into an irreversibly bound nonelutable form. The observed dependence of k on cSDS is then the result of competition between these two processes. Two-step experiments were performed in which the existence of the SDS-induced fastening of fibrinogen molecules to the surface was confirmed. A simple kinetic model was proposed in which two parameters related to the removal and anchoring subprocesses were introduced. The comparison between the experimental data and the model allowed us to get access to these parameters.

The question was asked whether tumour necrosis factor alpha (TNF) is involved in regulation of interferon gamma (IFNgamma) production by T cells. Monocytes were exposed to exogenous TNF or to TNF synthesis inhibitors (pentoxifylline, PTX and adriamycin, ADR) and then used as antigen (PPD) presenting cells for autologous T cells. The ability of T lymphocytes to release IFNgamma was assessed after 3 days of culture. Preincubation of monocytes with rTNF enhanced their ability to induce IFNgamma production while TNF synthesis inhibitors decreased it. Anti-TNF and anti-TNF-R2 monoclonal antibodies (mAbs) inhibited monocyte ability to present PPD for IFNgamma production which suggested that endogenously produced TNF by monocytes had to be released and acted on TNF-R2 on the monocyte surface. The enhancing effect of exogenous TNF was also abrogated by anti-TNF-R2 mAb. Pretreatment of monocytes with rTNF enhanced, while pretreatment with PTX decreased, PPD-induced IL-6 production. An increased production of IL-4 was found in cultures of PTX - treated, PPD-pulsed monocytes with T cells. This may indicate that in the relative absence of monocyte costimulatory signal(s), probably IL-6, Th2 cells are stimulated. These results indicate that TNF is involved in control of monocyte-mediated regulation of cytokine production by T cells.

The two fragments of HIV-1 gp120 molecule were synthesized to study their interaction with human monocytes. Previous observations indicated that recombinant gpl20 fragment (aa residues 410-511) encompassing CD4 binding region (rp 120cd) induced tumour necrosis factor a (TNF) production in monocytes, while a similar fragment (rp 120) not containing the CD4 binding sequence (aa 446-511) was inactive. This paper shows that rp 120cd depressed monocyte ability to present antigen (PPD) to autologous T lymphocytes while rp 120 was noninhibitory. The rp 120cd interacted with monocytes but not T lymphocytes. Anti-TNF receptor type A antibody (utr-1) prevented the depression of antigen presentation caused by rpl20cd, which suggested a role for TNF and its receptor. The depression of antigen presentation was seen only when monocytes were treated with rp 120cd before, but not after, pulse with antigen. Parallel changes were observed in PPD-induced IL-6 production. Thus, induction of TNF by gp 120 may be associated with impairment of antigen-presenting capacity of monocytes seen in AIDS patients.

Background: Transient hypogammaglobulinemia of infancy and isolated IgA deficiency are characterized by normal numbers of circulating B lymphocytes. It is likely that no single abnormality, but rather different factors, may be relevant for the delayed onset of IgG synthesis in transient hypogammaglobulinemia or for the differentiation defect of B cells in IgA deficiency. These factors may include defective production of cytokines or an abnormal response of B cells to various mediators. Alternatively, some cytokines may act as inhibitory factors of B-cell function. Methods: The ability of peripheral blood mononuclear cells from children with proved or probable transient hypogammaglobulinemia (30 patients) and IgA deficiency (15 patients) to secrete several cytokines on stimulation with phytohemagglutinin in vitro was analyzed. Results: An enhanced production of tumor necrosis factor (TNF)-@a, TNF-@b, and IL-10 was observed in transient hypogammaglobulinemia; whereas secretion of IL-1, IL-4, and IL-6 was essentially similar in the control and patient groups. Increased frequency of mononuclear cells secreting TNF-@a was seen in the patient groups. Apart from elevated production of TNF-@a, no other abnormalities in cytokine synthesis in selective IgA deficiency were observed. In vitro observations showed that exogenously added TNF-@a and TNF-@b inhibited IgG and IgA secretion by pokeweed mitogen-stimulated mononuclear cells. During follow-up of 10 children, normalization of serum IgG level was associated with a decrease in previously elevated TNF-@a and TNF-@b production, but IL-10 production remained unchanged. Conclusion: These results suggest that TNF may be involved in the regulation of IgG and IgA production and can be associated with an arrest of IgG and IgA switch of B cells in hypogammaglobulinemia. The balance between TNF and IL-10 may be important for the normal development of IgG-secreting B cells. (J Allergy Clin Immunol 1997;100:556-62.)

The effect of a soluble surfactant adsorption layer on the water evaporation was studied using an osmometric method. It was proved that Knauer's osmometer after appropriate modification of the measuring cell can be successfully used for a qualitative detection of the evaporation retardation. The osmometric behavior of the system was explained taking into account the adsorption properties of the surfactants and the heat effects accompanying the evaporation process. A measurable evaporation hindrance was registered only in case of sodium salts of myristic and palmitic acids at concentrations (close to the solubility limit) at which densely packed adsorption layers are formed. At the same time the latent heat of evaporation may cause a freezing of the higher density adsorption layer which is formed on the supersaturated solution drop.

Background: Melatonin, a pineal hormone that is biosynthesized from L-tryptophan, is known to scavenge oxygen free radicals and to be present in the gut, but little is known about the role of this hormone and its precursor, L-tryptophan, in protecting the gastric mucosa from damage accompanied by increase in the generation of oxygen radicals. Methods: This study was designed to determine the effects of melatonin and L-tryptophan on the formation of acute gastric lesions induced by stress and ischaemia reperfusion and, for comparison, by topical irritants such as 100% ethanol or acidified acetylsalicylic acid. Results: It was found that pretreatment with melatonin in doses ranging from 1.2 to lOmg/kg dose-dependently reduced the stress-induced gastric lesions and was accompanied by a reduction in blood-free radicals and by attenuation of the fall in gastric blood flow. L-tryptophan applied intragastrically in doses ranging from 1 to lOOmg/kg also reduced dose-dependently the lesions induced by stress; this effect too was accompanied by a rise in gastric blood flow. Pretreatment with indomethacin, to block the biosynthesis of prostaglandins, significantly augmented the lesions produced by stress and completely abolished the protective effects of melatonin or L-tryptophan. Both melatonin and tryptophan reduced the formation of acute gastric lesions provoked by ischaemia reperfusion; this was accompanied by an increase in gastric blood flow. In contrast, melatonin and L-tryptophan failed to influence acute gastric lesions induced by topical irritants such as 100% ethanol or acidified aspirin. Conclusions: Melatonin and L-tryptophan protect the gastric mucosa from damage by stress and ischaemia reperfusion, and this action is mediated, at least in part, by the limitation in the free radicals, the stimulation of mucosal generation of PG and by the increase in gastric blood flow.

The HIV-1 gp120 recombinant protein fragment encompassing aa residues 410-511, that contains the CD4 binding region (rp120cd), and fragment aa 446-511, which lacks the sequence responsible for CD4 binding (rp120), were synthesized to study their ability to induce TNF synthesis in human monocytes. The rp120cd stimulated TNFα secretion by monocytes while the rp120 and full-length recombinant protein (FL gp120), used as control, failed to do so. However, FL gp120 stimulated peripheral blood mononuclear cells (PBMC) and lymphocytes for TNF production and this was inhibited by anti-CD4 MAb. The rp120cd also caused TNF secretion by PBMC that was not blocked by this antibody. Furthermore, FL gp120 but not rp120cd inhibited anti-CD4 mAb binding to CEM cells. Hence, FL gp120 may cause TNF release from lymphocytes by binding to CD4, while rp120cd interacts with monocytes but not lymphocytes and induces TNF production by a mechanism not involving CD4 binding. Unexpectedly, FL gp120 but not rp120cd stimulated IL-6 secretion and IL-6 mRNA synthesis in monocytes. The FL gp120-induced production of IL-6 by monocytes was inhibited by anti-CD4 monoclonal antibody (MAb). Thus, there may be different requirements for TNF induction in lymphocytes and monocytes stimulated with various preparations of gp120 and for the selective induction of cytokines in monocytes. The enhanced production of TNF in HIV infection and AIDS may involve distinct cellular sources and different mechanisms.

Not Available

We have examined the ability of macrophages (Mphi) to transmit T-cell derived suppressor signals to other T cells. The suppressor signal studied is an antigen-specific factor which suppresses the ability of adoptively transferred, sensitized lymphocytes to express contact hypersensitivity in normal recipients. We have found that this factor binds to peritoneal exudate Mphi via cell surface structures which can be blocked with heat-aggregated gamma globulin. Dead (HK) Mphi bind the factor but fail to present it in a functional way to assay (immune) T cells, whereas live (L) Mphi perform both functions. Further, L Mphi can retrieve the factor in an active form from the surfaces of HK Mphi. Based on these and other findings (1-5), we discuss the possibility that Mphi may play as important a role in presenting T-cell communication signals to the cells of the immune system as they do in presenting antigen.

The semen of bulls standing at A.I. Centres was examined virologically. Cytopathogenic agents were isolated from 17 per cent of 194 semen samples. The isolated viruses were preliminarily classified as entero-like, rheo-like and Papova-like viruses.

Contact sensitivity skin reactions were produced in mice by immunization with 2-phenyl-4-ethoxymethylene oxazolone (oxazolone) and detected by the increase in ear thickness after challenging the ears with 2% oxazolone. These skin reactions can be transferred from immunized donors to irradiated recipients by peritoneal exudate cells induced by thioglycollate. The peritoneal exudate cells were separated into purified macrophage and purified lymphocyte populations. Both cell populations transferred skin reactions. However, their time course was different. The reactions produced by lymphocytes were greater at 24 hr than at 12 hr while the reactions produced by macrophages declined slightly between 12 and 24 hr. The working hypothesis was formed that the peritoneal lymphocytes conveyed a factor (presumptive cytophilic antibody) to peritoneal macrophages which enabled them to transfer ear reactions. Experiment showed that peritoneal and lymph node lymphocytes from sensitized donors within a Millipore chamber conveyed a factor to macrophages outside the chamber which enabled them to transfer ear reactions. In contrast, peritoneal macrophages (from sensitized donors) within the chamber and peritoneal lymphocytes outside the chamber were inactive. These findings suggested that there are three modes of immunological tissue damage: hypersensitivity mediated by lymphocytes (classical delayed hypersensitivity), hypersensitivity mediated by circulating antibody (classical immediate type hypersensitivity), and hypersensitivity mediated by macrophages which have passively acquired a factor (macrophage-mediated hypersensitivity).

The classical example of genetic restriction is associative recognition, the finding that cytotoxic T-cell killing requires matching between part of the major histocompatibility complex (MHC) of the stimulating cell and the target cell1,2. Its analysis would be facilitated by the study of a system in which antigen-specific T suppressor factor (TSF) was genetically restricted in its interaction with haptenized cells. However, only one such system is known3,4, although there are several systems in which the TSF must be syngeneic with other cells5–8. We now describe a genetically restricted TSF which arms an acceptor T cell. This acceptor cell shows some resemblance to the auxiliary T suppressor (Ts) cell, the acceptor T cell and the Ts3described elsewhere5,6,9. In the presence of antigen (haptenized spleen cells) the armed acceptor cell releases a nonspecific inhibitor of the passive transfer of contact sensitivity (see. Fig. 1). The important finding is that the antigen will only trigger the release of the nonspecific inhibitor when there is matching in the I–J region between the TSF and the haptenized cell used as a source of the triggering antigen.

The case history of a 10-year-old boy with chronic granulomatous disease (CGD) and gastric obstruction is presented. First abdominal symptoms occurred at 4 years of age when antral narrowing was detected. Due to unresponsiveness to antibiotic and steroid treatment, salazosulfapyridine therapy was initiated. Objective remission was observed within 3 months and salazosulfapyridine was withdrawn after a further 6 months of therapy. At 6 years of age clinical and radiological recurrence of gastric obstruction was observed. Salazosulfapyridine was reinstated and continued as maintenance therapy. The child has been well for more than 4 years. Salazosulfapyridine therapy can be recommended as safe conservative treatment of gastric obstruction in CGD.

THE lymph node cells of mice rendered unresponsive by the injection of picryl sulphonic acid (PSA) depress the passive transfer of contact sensitivity1. When the mice are also painted with picryl chloride the lymph node cells produce suppressor factor in vitro. This factor depresses the passive transfer of contact sensitivity by immune cells and its production is T-cell dependent2. Here we show that suppressor factor(s) has a molecular weight ∼50,000 and that it is absorbed by and can be eluted from specific antigen in the form of picrylated albumin attached to Sepharose beads.

Two hundred and seventeen patients with advanced gastric cancer were classified according to the resectability of the tumour into two groups: I, resectable (non-radical surgery), 99 patients, and II, non-resectable carcinoma, 118 patients. Within each group patients were randomly assigned to receive 5-fluorouracil (5-FU) + BCG, 5-FU, or no further treatment (surgery only). BCG was given by scarification. A 2-year follow-up is reported. The group of patients with resectable tumours and receiving chemoimmunotherapy had a statistically significant prolongation of survival compared with the 5-FU and surgery only groups. No differences in survival were observed between these treatment modalities in patients with non-resectable tumour. These observations indicate that chemoimmunotherapy may be of benefit for a selected group of patients with gastric cancer.

Background: The size of the transcatheter heart valves (THV) is overestimated up to 20% based on aortic annulus diameter measured using computed tomography (CT). However, the prosthesis may not be fully expanded during implantation. THV underexpansion might have detrimental clinical consequences. Purpose The aim of this study was to define the degree of underexpansion degree of different THVs after implantation, introduced as the shrinking index. Methods: In total we enrolled 114 patients (68 men, 79 ± 8 years old) who underwent transcatheter aortic valve implantation (TAVI) with the self-expanding CoreValve (n=28 patients), mechanically expanded Lotus valve (n= 37) or balloon expandable Edwards SAPIEN XT (n=18) and Edwards SAPIEN 3 (n= 31). The cover index of the THV was calculated as the percentage difference of the nominal prosthesis size and annulus diameter measured using CT. Intraprocedural transesophageal echocardiography (TEE) was performed to determine the size of the THV inflow after implantation. The shrinking index was calculated as the percentage of the difference between the inflow size by TEE and the nominal prosthesis size divided by prosthesis size. Results: Cover index per CT assessment before TAVI was 18 ± 7% for CoreValve, 2 ± 4% for Lotus, 9 ± 5% for Edwards SAPIEN and 4 ± 5% for Edwards SAPIEN 3 (ANOVA p < 0.001, Corevalve was significantly larger than the others). Compared with aortic annulus diameter measured using TEE in long axis view, the overestimation increased to 28 ± 9% for CoreValve, 12 ± 8% for Lotus, 18 ± 12% for Edwards SAPIEN and 12 ± 8% for Edwards SAPIEN 3 (ANOVA p < 0.001, Corevalve was significantly larger than the others). Conversely, the shrinking index after TAVI was -31 ± 6% for CoreValve, -20 ± 5% for Lotus, -22 ± 6% for SAPIEN XT and -19 ± 5% for SAPIEN 3 (ANOVA p < 0.001, Corevalve was significantly larger than the others). The interobserver variability (relative difference) of TEE in measuring the aortic annulus and prosthesis inflow was 6 ± 5% and 7 ± 5% respectively. Conclusion: The shrinking index determines the degree of THV underexpansion after TAVI and can be reliably measured with TEE. The self-expanding CoreValve tended to be under-expanded the most, indicated by the largest shrinking index, while the under-expansion degree was comparable between Lotus valve, SAPIEN XT and SAPIEN 3. The clinical implications of the shrinking index requires further study.

Gershon and Kondo1provided evidence that T cells from unresponsive mice depressed the antibody response of normal mice to sheep erythrocytes, and introduced the term “infectious tolerance”. Jacobson et al.2showed that T cells were responsible for the prolonged allotypic suppression in mice which may be a model for immunological unresponsiveness. Unresponsiveness to picryl chloride (PCI) produced by pretreatment with picryl sulphonic acid (PSA) is also an example of infectious tolerance (positive unresponsiveness)3. In particular, the transfer of lymph node cells from unresponsive to normal mice limited the recipient's contact sensitivity response to PCI. These findings raised the question whether the suppressor cell responsible for positive unresponsiveness was a T cell.