False belief reasoning in the brain: An ERP study

Understanding others mind and interpersonal interaction are the cognitive basis of successful social interactions. People's mental states and behaviors rely on their holding beliefs for self and others. To investigate the neural substrates of false belief reasoning, the 32 channels event-related potentials (ERP) of 14 normal adults were measured while they understood false-belief and true belief used de-ceptive appearance task. After onset of the false-belief or true-belief questions, N100, P200 and late negative component (LNC) were elicited at centro-frontal sites. Compared with true belief, false belief reasoning elicited significant declined LNC in the time window from 400 to 800 ms. The source analysis of difference wave (False minus True) showed a dipole located in the middle cingulated cortex. These findings show that false belief reasoning probably included inhibitive process.     

Early false-belief understanding in traditional non-Western societies

The psychological capacity to recognize that others may hold and act on false beliefs has been proposed to reflect an evolved, species-typical adaptation for social reasoning in humans; however, controversy surrounds the developmental timing and universality of this trait. Cross-cultural studies using elicited-response tasks indicate that the age at which children begin to understand false beliefs ranges from 4 to 7 years across societies, whereas studies using spontaneous-response tasks with Western children indicate that false-belief understanding emerges much earlier, consistent with the hypothesis that false-belief understanding is a psychological adaptation that is universally present in early childhood. To evaluate this hypothesis, we used three spontaneous-response tasks that have revealed early false-belief understanding in the West to test young children in three traditional, non-Western societies: Salar (China), Shuar/Colono (Ecuador) and Yasawan (Fiji). Results were comparable with those from the West, supporting the hypothesis that false-belief understanding reflects an adaptation that is universally present early in development.     

Processing Demands Impact 3-Year-Olds’ Performance in a Spontaneous-Response Task: New Evidence for the Processing-Load Account of Early False-Belief Understanding

Prior to age four, children succeed in non-elicited-response false-belief tasks but fail elicited-response false-belief tasks. To explain this discrepancy, the processing-load account argues that the capacity to represent beliefs emerges in infancy, as indicated by early success on non-elicited-response tasks, but that children’s ability to demonstrate this capacity depends on the processing demands of the task and children’s processing skills. When processing demands exceed young children’s processing abilities, such as in standard elicited-response tasks, children fail despite their capacity to represent beliefs. Support for this account comes from recent evidence that reducing processing demands improves young children’s performance: when demands are sufficiently reduced, 2.5-year-olds succeed in elicited-response tasks. Here we sought complementary evidence for the processing-load account by examining whether increasing processing demands impeded children’s performance in a non-elicited-response task. 3-year-olds were tested in a preferential-looking task in which they heard a change-of-location false-belief story accompanied by a picture book; across children, we manipulated the amount of linguistic ambiguity in the story. The final page of the book showed two images: one that was consistent with the main character’s false belief and one that was consistent with reality. When the story was relatively unambiguous, children looked reliably longer at the false-belief-consistent image, successfully demonstrating their false-belief understanding. When the story was ambiguous, however, this undermined children’s performance: looking times to the belief-consistent image were correlated with verbal ability, and only children with verbal skills in the upper quartile of the sample demonstrated a significant preference for the belief-consistent image. These results support the processing-load account by demonstrating that regardless of whether a task involves an elicited response, children’s performance depends on the processing demands of the task and their processing skills. These findings also have implications for alternative, deflationary accounts of early false-belief understanding.     

Dogs cannot bark: event-related brain responses to true and false negated statements as indicators of higher-order conscious processing

The present study investigated event-related brain potentials elicited by true and false negated statements to evaluate if discrimination of the truth value of negated information relies on conscious processing and requires higher-order cognitive processing in healthy subjects across different levels of stimulus complexity. The stimulus material consisted of true and false negated sentences (sentence level) and prime-target expressions (word level). Stimuli were presented acoustically and no overt behavioral response of the participants was required. Event-related brain potentials to target words preceded by true and false negated expressions were analyzed both within group and at the single subject level. Across the different processing conditions (word pairs and sentences), target words elicited a frontal negativity and a late positivity in the time window from 600-1000 msec post target word onset. Amplitudes of both brain potentials varied as a function of the truth value of the negated expressions. Results were confirmed at the single-subject level. In sum, our results support recent suggestions according to which evaluation of the truth value of a negated expression is a time- and cognitively demanding process that cannot be solved automatically, and thus requires conscious processing. Our paradigm provides insight into higher-order processing related to language comprehension and reasoning in healthy subjects. Future studies are needed to evaluate if our paradigm also proves sensitive for the detection of consciousness in non-responsive patients.     

The predator-avoidance effect: an evolved constraint on emerging theory of mind

The present research examined whether children's ability to impute false belief is overridden or impaired by content that activates an early-developing, prepotent motivational system: predator avoidance. In three studies, children aged 3 to 8 years completed variants of a false-belief test, including analogous predator-avoidance and playmate-avoidances scenarios, in which passing the test meant having the focal character get caught by the pursuer. The proportion of correct answers in the playmate-avoidance scenario was reliably greater than in the predator-avoidance scenario, though this effect largely dissipated by 7 to 8 years of age. Enhanced predatory stimuli significantly increased the frequency of false-belief errors in the predator-avoidance scenario (Study 3). Analysis of children's justifications revealed that predator-avoidance false-belief errors were overwhelming motivated by a desire for the prey to avoid the predator (Study 2). The predator-avoidance effect was not an artifact of children generally performing better in playmate than predator–prey scenarios (Studies 1 and 3), the predator-avoidance scenario simply evoking strong emotions (Study 3), or differences between children in their knowledge of predator–prey relationships (Study 1) or executive-function abilities (Study 2). Findings support the hypothesis that activation of the predator-avoidance system generates prepotent response patterns that impair or override full consideration of the mental states of the prey characters in false-belief stories.     

Evidence for cognition without grammar from causal reasoning and 'theory of mind' in an agrammatic aphasic patient

Understanding the inter-relationship between language and thought is fundamental to the study of human cognition [1] [2] [3]. Some investigators have proposed that propositions in natural language serve to scaffold thinking, by providing, for example, a sequential structure to a massively parallel process [4]. Others have maintained that certain thoughts, such as inferring the mental states of others, termed 'theory of mind' (ToM) reasoning, and identifying causal relationships, necessarily involve language propositions [5]. It has been proposed that ToM reasoning depends upon the possession of syntactic structures such as those that permit the embedding of false propositions within true statements ('Mary knows that John (falsely) thinks chocolates are in the cupboard') [6]. The performance on reasoning tasks of individuals with severe agrammatic aphasia (an impairment of language following a lesion of the perisylvian areas of the language-dominant hemisphere) offers novel insights into the relation between grammar and cognition. We report the unusual case of a patient with agrammatic aphasia of such severity that language propositions were not apparently available at an explicit processing level in any modality of language use. Despite this profound impairment in grammar, he displayed simple causal reasoning and ToM understanding. Thus, reasoning about causes and beliefs involve processes that are independent of propositional language.     

Are All Beliefs Equal? Implicit Belief Attributions Recruiting Core Brain Regions of Theory of Mind

Humans possess efficient mechanisms to behave adaptively in social contexts. They ascribe goals and beliefs to others and use these for behavioural predictions. Researchers argued for two separate mental attribution systems: an implicit and automatic one involved in online interactions, and an explicit one mainly used in offline deliberations. However, the underlying mechanisms of these systems and the types of beliefs represented in the implicit system are still unclear. Using neuroimaging methods, we show that the right temporo-parietal junction and the medial prefrontal cortex, brain regions consistently found to be involved in explicit mental state reasoning, are also recruited by spontaneous belief tracking. While the medial prefrontal cortex was more active when both the participant and another agent believed an object to be at a specific location, the right temporo-parietal junction was selectively activated during tracking the false beliefs of another agent about the presence, but not the absence of objects. While humans can explicitly attribute to a conspecific any possible belief they themselves can entertain, implicit belief tracking seems to be restricted to beliefs with specific contents, a content selectivity that may reflect a crucial functional characteristic and signature property of implicit belief attribution.     

The Neural Basis of Testable and Non-Testable Beliefs

Beliefs about the state of the world are an important influence on both normal behavior and psychopathology. However, understanding of the neural basis of belief processing remains incomplete, and several aspects of belief processing have only recently been explored. Specifically, different types of beliefs may involve fundamentally different inferential processes and thus recruit distinct brain regions. Additionally, neural processing of truth and falsity may differ from processing of certainty and uncertainty. The purpose of this study was to investigate the neural underpinnings of assessment of testable and non-testable propositions in terms of truth or falsity and the level of certainty in a belief. Functional magnetic resonance imaging (fMRI) was used to study 14 adults while they rated propositions as true or false and also rated the level of certainty in their judgments. Each proposition was classified as testable or non-testable. Testable propositions activated the DLPFC and posterior cingulate cortex, while non-testable statements activated areas including inferior frontal gyrus, superior temporal gyrus, and an anterior region of the superior frontal gyrus. No areas were more active when a proposition was accepted, while the dorsal anterior cingulate was activated when a proposition was rejected. Regardless of whether a proposition was testable or not, certainty that the proposition was true or false activated a common network of regions including the medial prefrontal cortex, caudate, posterior cingulate, and a region of middle temporal gyrus near the temporo-parietal junction. Certainty in the truth or falsity of a non-testable proposition (a strong belief without empirical evidence) activated the insula. The results suggest that different brain regions contribute to the assessment of propositions based on the type of content, while a common network may mediate the influence of beliefs on motivation and behavior based on the level of certainty in the belief.     

Distinct in vivo and in vitro cytokine profiles of draining lymph node cells in acute and chronic phases of contact hypersensitivity: importance of a type 2 cytokine-rich cutaneous milieu for the development of an early-type response in the chronic phase.

Although regional lymph nodes (LN) have been extensively studied as rich sources of effector T cells in contact hypersensitivity (CH), it remains unknown whether T cell responses in the LN reflect those in effector skin sites. We previously showed that repeated elicitation of CH results in a shift in the time course of Ag-specific CH from a delayed-type hypersensitivity response to an early-type response, a reflection of a shift in cutaneous cytokine expression from a type 1 to a type 2 profile. To investigate whether repeated elicitation of CH could also drive T cell development to the type 2 phenotype in the regional draining LN, sequential cytokine gene expression after hapten application was assessed during both the acute and the chronic phase of CH. In the draining LN the shift to type 2 cytokine production was also observed, but more mixed patterns of responses were induced than in the corresponding skin sites. The chronic LN cells (LNC), when stimulated in vitro, produced markedly lower levels of type 1 cytokines and higher levels of type 2 cytokines than the acute LNC. A successful passive transfer of an early-type response by the LNC was only induced in the recipient mice when the skin sites chronically treated with hapten were elicited. These results indicate that an early-type response by regional LNC would take place only in a milieu with sufficient levels of type 2 cytokines.     

松嫩草地66种草本植物叶片性状特征

植物叶片功能性状及其相互关系越来越受到关注.以松嫩草地66种草本植物为研究对象,测量叶片干物质含量、比叶面积、叶片厚度、叶片氮含量、叶片磷含量、叶绿素含量和类胡萝卜素含量,检验性状间的相互关系,比较不同功能群(多年生根茎禾草,多年生丛生禾草,多年生杂类草,1年生或2年生草本)间性状的差异性.结果表明,叶片厚度变异系数最大,比叶面积、叶片氮含量、叶片磷含量、叶绿素含量和类胡萝卜素含量之间存在显著的正相关关系;叶片于物质含量与叶片磷含量没有显著的相关关系,与其它叶片性状呈显著的负相关关系;叶片厚度只与叶片干物质含量和比叶面积呈显著的负相关关系,与其它叶片性状不相关.叶片干物质含量、比叶面积、叶片厚度、叶片氮、磷含量在4个功能群间差异显著,叶绿素含量和类胡萝卜素含量在各个功能群间差异不显著;多年生根茎禾草和多年生丛生禾草叶片的7个性状差异不显著;多年生根茎禾草和多年生丛生禾草的叶片干物质含量高于多年生杂类草和1年生或2年生草本,其它性状小于这两个功能群.     

Cooperation and deception recruit different subsets of the theory-of-mind network

The term "theory of mind" (ToM) describes an evolved psychological mechanism that is necessary to represent intentions and expectations in social interaction. It is thus involved in determining the proclivity of others to cooperate or defect. While in cooperative settings between two parties the intentions and expectations of the protagonists match, they diverge in deceptive scenarios, in which one protagonist is intentionally manipulated to hold a false belief about the intention of the other. In a functional magnetic resonance imaging paradigm using cartoons showing social interactions (including the outcome of the interaction) between two or three story characters, respectively, we sought to determine those brain areas of the ToM network involved in reasoning about cooperative versus deceptive interactions. Healthy volunteers were asked to reflect upon the protagonists' intentions and expectations in cartoons depicting cooperation, deception or a combination of both, where two characters cooperated to deceive a third. Reasoning about the mental states of the story characters yielded substantial differences in activation patterns: both deception and cooperation activated bilateral temporoparietal junction, parietal and cingulate regions, while deception alone additionally recruited orbitofrontal and medial prefrontal regions. These results indicate an important role for prefrontal cortex in processing a mismatch between a character's intention and another's expectations as required in complex social interactions.     

Regulation of the in vitro anamnestic antibody response by cyclic AMP. III. Cholera enterotoxin induces lymph node cells to release soluble factor(s) which enhance(s) antibody synthesis by antigen-treated lymph node cells.

Unprimed or KLH-primed rabbit lymph node cells were pulsed with cholera enterotoxin or KLH for 2 hr and washed. KLH-treated LNC were mixed with equal numbers of CT-treated LNC or boiled CT-treated LNC. Cocultivation of CT-treated LNC with KLH-treated cells resulted in at least a 100% increase in antibody synthesis compared to control cultures. Delaying cocultivation for 24 hr reduced enhancement to 25%. Thus it appears that an early event—before 24 hr—is involved in CT enhancement. Using ¹²⁵I-CT, it was shown that these effects were not due to CT carry-over. When KLH- and CT-pulsed LNC were cultured in chambers separated by polycarbonate membranes (0.2- to 0.4-μm pore size) antibody production was enhanced 50–80%. Supernates of CT-treated LNC also enhanced antibody production by KLH-treated LNC. These results suggest that CT triggers the release of soluble factor(s) which enhance(s) antibody synthesis by antigen-primed and antigen-challenged LNC.     

Suppressing effects of purified eosinophils derived from guinea pigs sensitized with Ascaris antigen on lymphocyte-blastformation

Highly purified eosinophil (EOS) fractions were obtained from peritoneal exudate cells of guinea pigs immunized with with Ascaris lumbricoides suum antigen (Asc). These Eos suppressed the in vitro DNA synthesis of the lymph node cells (LNC) sensitized with Asc and then activated by this antigen or phytohemagglutinin (PHA). Although addition of Eos did not effect the viability of LNC in vitro, the blastformation of LNC was suppressed remarkably when 5-10 X 10(5) purified Eos were added to 10(6) LNC within 48 hr after the start of stimulation by Asc. The suppressive effects of Eos on the blastformation of LNC immunized with complete Freund's adjuvant with or without ovalbumin were observed when stimulated with purified protein derivates or ovalbumin. Such suppression were observed beyond the barrier of animal strain specificity; Eos from Hartley guinea pigs suppressed proliferation of LNC from either strain 13 or strain 2, and Eos from strain 13 suppressed that from strain 2. Such suppressing activity of Eos was reduced by heating them at 56 C for 1 hr or by sonication.     

Assessment of syngeneic cell-mediated immunity to mouse mammary tumors by three different assays

Summary The purpose of this study was to compare the MCT, CRT, and Winn assays for assessment of CMI to syngeneic tumors. Spontaneous and MMTV-induced mammary tumors in Balb/c and Balb/cfC₃H mice were used. LNC were obtained at various times relative to S.C. injection of sensitizing tumor cells and surgical removal of the outgrowth. In direct comparison to Winn assays, CRT often gave false negatives (i.e., LNC could inhibit tumor growth in the Winn assay without being cytolytic), but when LNC were cytolytic in the CRT, they inhibited in Winn assays. Thus, a positive CRT was associated with a positive Winn assay. In contrast, results from MCT tests were generally not associated with those obtained by CRT or Winn assays. This divergence in assays was independent of differences in status of the LNC donor. With all three assays, stimulation of tumor growth or increased survival was occasionally observed. For the CRT this was manifested in the release of smaller amounts of ⁵¹Cr in the presence of immune LNC than in the presence of normal LNC. For MCT and Winn assays it was seen in better tumor growth after treatment with LNC than after treatment with medium alone. Detection of this phenomenon was independent among the three assays.Data from the CRT and Winn assays were analyzed to see whether they correlated with in vivo behavior of the sensitizing tumors. Detection of CMI by these tests was associated with tumors growing out after relatively long latency periods, but was independent of tumor growth rate. This is in contrast to our previously reported analysis of MCT data, in which detection of CMI was associated with slower growth rate but was independent of the latency period (Hager et al., 1978).Abbreviations CMI cell-mediated immunity - CRT chromium-release test - MCT microcytotoxicity test - MMTV murine mammary tumor virus - LDA lymphocyte-dependent antibody - LNC lymph node cells - SBF serum-blocking factors - SC subcutaneous - TCM tissue culture medium     

Procedural Metacognition and False Belief Understanding in 3- to 5-Year-Old Children

Some studies, so far limited in number, suggest the existence of procedural metacognition in young children, that is, the practical capacity to monitor and control one’s own cognitive activity in a given task. The link between procedural metacognition and false belief understanding is currently under theoretical discussion. If data with primates seem to indicate that procedural metacognition and false belief understanding are not related, no study in developmental psychology has investigated this relation in young children. The present paper aims, first, to supplement the findings concerning young children’s abilities to monitor and control their uncertainty (procedural metacognition) and, second, to explore the relation between procedural metacognition and false belief understanding. To examine this, 82 3- to 5-year-old children were presented with an opt-out task and with 3 false belief tasks. Results show that children can rely on procedural metacognition to evaluate their perceptual access to information, and that success in false belief tasks does not seem related to success in the task we used to evaluate procedural metacognition. These results are coherent with a procedural view of metacognition, and are discussed in the light of recent data from primatology and developmental psychology.     

Psychosis-Proneness and Neural Correlates of Self-Inhibition in Theory of Mind

Impaired Theory of Mind (ToM) has been repeatedly reported as a feature of psychotic disorders. ToM is crucial in social interactions and for the development of social behavior. It has been suggested that reasoning about the belief of others, requires inhibition of the self-perspective. We investigated the neural correlates of self-inhibition in nineteen low psychosis prone (PP) and eighteen high PP subjects presenting with subclinical features. High PP subjects have a more than tenfold increased risk of developing a schizophrenia-spectrum disorder. Brain activation was measured with functional Magnetic Resonance Imaging during a ToM task differentiating between self-perspective inhibition and belief reasoning. Furthermore, to test underlying inhibitory mechanisms, we included a stop-signal task. We predicted worse behavioral performance for high compared to low PP subjects on both tasks. Moreover, based on previous neuroimaging results, different activation patterns were expected in the inferior frontal gyrus (IFG) in high versus low PP subjects in self-perspective inhibition and simple response inhibition. Results showed increased activation in left IFG during self-perspective inhibition, but not during simple response inhibition, for high PP subjects as compared to low PP subjects. High and low PP subjects showed equal behavioral performance. The results suggest that at a neural level, high PP subjects need more resources for inhibiting the self-perspective, but not for simple motor response inhibition, to equal the performance of low PP subjects. This may reflect a compensatory mechanism, which may no longer be available for patients with schizophrenia-spectrum disorders resulting in ToM impairments.     

Immunosuppression of experimental allergic encephalomyelitis. III. In vitro evidence for induction of suppressor T lymphocytes in draining lymph node cells of animals immunized with myelin basic protein complexed to lipopolysaccharides

We recently demonstrated that Lewis rats immunized with bacterial lipopolysaccharides (LPS) precomplexed to guinea pig myelin basic protein (BP) in complete Freund's adjuvant were less effective in inducing experimental allergic encephalomyelitis (EAE) than BP-immunized controls. When tested in vitro both lymph node cells (LNC) and spleen cells (SpC) of animals immunized with BP-LPS were less effective in proliferative responses to various mitogens, which included phytohemagglutinin, concanavalin A, purified protein derivative of tuberculin, LPS, and BP. Of importance immunization of rats with BP complexed to LPS results in the generation of cells in lymph nodes of these animals that suppress the mitogenic response of BP-immunized LNC and also SpC in mixed lymphocyte cultures. The suppressive effect of these cells in mixed lymphocyte culture reaction was found specifically in response to BP and to a lesser extent to LPS in LNC. SpC of BP-LPS immunized animals did not suppress the proliferative response to SpC of BP-immunized animals. Treatment of these LNC with antithymocyte serum and complement abolished this suppressive effect of LNC, suggesting that the immunoregulatory cells in LNC of BP-LPS immunized animals are suppressor T lymphocytes. The parallel between the in vitro induction of suppressor T lymphocytes in the draining LNC and the function of LPS in the development of EAE in Lewis rats suggests a possible immunologic significance of the effect.     

Lymphoid cell subpopulations. II. Characterization of cell populations responsible for syngery in the mixed lymphocyte interaction.

Mixtures of isogeneic lymph node cells (LNC) and thymocytes (TC) exhibit far greater responsiveness in the murine MLI, as measured by proliferation and development of cytotoxic effector cells, than either cell type cultured alone. Pretreatment of either lnc or TC with mitomycin-C or ultraviolet irradiation completely abolished their synergistic interaction. Administration of cortisone acetate to cell donors 20 hr before sacrifice reduced the capacity of LNC and enhanced the capacity of TC to synergize. The LNC and TC populations participating in synergy, were found to be thymus dependent. LNC were shown to be responsible for the bulk of proliferative and effector activity observed in synergizing cultures, whereas TC appeared to amplify the activation of LNC. These findings provide the basis for a three cell model of MLI responsiveness.     

Amplification of lymph node cell tube leukocyte adherence inhibition (LAI) reactivity by leukocyte adherence inhibition factor (LAIF)

This investigation examines the immunologic basis for specific antigen-induced tube leukocyte adherence inhibition (LAI) reactivity of draining lymph node cells (LNC) from dogs with canine transmissible venereal sarcoma (CTVS). CTVS regressor LNC, macrophage-depleted LNC, and enriched T lymphocyte fractions, but not enriched B lymphocyte fractions, were specifically reactive to CTVS antigen extract in direct tube LAI. In addition, regressor LNC amplified tube LAI responses by generating supernatants with leukocyte adherence inhibition factor (LAIF) activity for normal dog indicator LNC and enriched peripheral blood mononuclear cells (PBMC) in an indirect tube LAI assay. However, macrophage-depleted LNC and enriched T lymphocyte fractions failed to generate supernatants with LAIF activity, suggesting that macrophage accessory cells play a central role in the amplification of tube LAI. Interestingly, CTVS regressor peripheral blood leukocytes (PBL) and PBMC, which were specifically reactive in direct tube LAI, also failed to generate supernatants with LAIF activity. These findings demonstrate a distinction between LAIF-mediated amplification and direct tube LAI reactivity, and suggest that leukocyte populations with differing cellular proportions and from different immunologic compartments may participate in tube LAI via different mechanisms.     

Immunogenetic differences between lymph node cell and bone marrow cell grafts in irradiated mice

C3H lymph node cell (LNC) grafts, but not bone marrow cell (BMC) grafts, were resisted by lethally irradiated NZB, (C57BL × NZB)F1, and (C57BL/6 × DBA/2)F1 mice. BALB/ c hosts did not resist C3H LNC, suggesting that Ir-like genes regulate resistance to such grafts. Cyclophosphamide, silica particles, and ⁸⁹Sr pretreatments of prospective host mice resulted in successful proliferation of C3H LNC in most instances. These agents were known to abrogate resistance to incompatible BMC grafts. The determinants for antigens recognized on LNC appear to map in or near the D region of H-2. LNC grafts of all H-2^k strains tested (C3H, CBA, C58, C57BR) were strongly resisted while A, C3H.A, B10.A(5R), A.TL, and A.Tla^b LNC grafts were not strongly resisted by NZB hosts. Grafts of H-2^b (C57BL/6, C57BL/10, 129) LNC, or BMC are resisted by NZB or (C57BL/6 × DBA/2)F1 hosts. (C3H × C57BL)F1 LNC but not BMC were resisted by similar hosts. (C57BL/6 × DBA/2)F1 mice were injected with C57BL/6 spleen cells four times to induce specific “unresponsiveness” to parental-strain Hemopoietic histocompatibility (Hh) antigens. Unresponsiveness was induced to C57BL/6 BMC, as expected, but C57BL/6 and C3H LNC grafts were resisted despite the spleen cell injections. The data suggest that the antigens recognized during rejection of C3H LNC are not expressed on C3H BMC. It is even conceivable that Hh antigens on C57BL/6 BMC and LNC have separate determinants. Alternatively, the injections of C57BL/6 spleen cells may have induced an anti-idiotypic response that was capable of eliminating C57BL/6 LNC by a different effector mechanism.