Cells Responsive Research Articles

Effects of shape-discrimination training on the selectivity of inferotemporal cells in adult monkeys.

Through extensive training, humans can become "visual experts, " able to visually distinguish subtle differences among similar objects with greater ease than those who are untrained. To understand the neural mechanisms behind this acquired discrimination ability, adult monkeys were fully trained to discriminate 28 moderately complex shapes. The training effects on the stimulus selectivity of cells in area TE of the inferotemporal cortex were then examined in anesthetized preparations. Area TE represents a later stage of the ventral visual cortical pathway that is known to mediate visual object discrimination and recognition. The recordings from the trained monkeys and untrained controls showed that the proportion of TE cells responsive to some member of the 28 stimuli was significantly greater in the trained monkeys than that in the control monkeys. Cell responses recorded from the trained monkeys were not sharply tuned to single training stimuli, but rather broadly covered several training stimuli. The distances among the training stimuli in the response space spanned by responses of the recorded TE cells were significantly greater in the trained monkeys than those in the control monkeys. The subset of training stimuli to which individual cells responded differed from cell to cell with only partial overlaps, suggesting that the cells responded to features common to several stimuli. These results are consistent with a model in which visual expertise is acquired through the development of differential responses by inferotemporal cells to the images of relevant objects.

Detection of antigen-specific T cell cytokine expression in whole blood by flow cytometry

We have recently described a highly sensitive flow cytometric technique, based on the ability to detect single cell expression of cytokines, to simultaneously quantitate and phenotypically characterize antigen-specific memory/effector T cells in PBMC cultures. In this report, we describe a simplified procedural modification which enables the rapid detection of low frequency memory CD4 + and CD8 + T cells expressing cytokines in response to soluble antigen in whole blood. When compared with T cell responses in PBMC cultures, whole blood cultures demonstrated similar but slightly higher percentages of T cells responsive to specific antigen. In addition, T cell responses to cytomegalovirus in whole blood were observed only in sensitized (seropositive) individuals, and CD4 + T cell responses could be blocked by anti-class II MHC antibodies. This procedure may provide a means to examine direct effects of pharmacological drug concentrations on T cell immunity in clinical samples.

The use of computer-assisted video image analysis for the quantification of CD8 + T lymphocytes producing tumor necrosis factor α spots in response to peptide antigens

Enzyme-linked immunospot (ELISPOT) analysis is a sensitive technique for the detection and quantification of single T lymphocytes forming cytokine spots after antigen contact in vitro. Herein computer-assisted video image analysis (CVIA) was applied to automatically determine the number and size of tumor necrosis factor α (TNF- α) spots formed by single blood-derived CD8 + T cells after contact with peptide-loaded target cells. With CVIA and TNF- α ELISPOT analysis we quantified CD8 + T cells responsive to HLA-A2.1-binding tyrosinase and influenza matrix peptides in healthy donors. We followed the course of the virus-specific T cell response in two HLA-A2-positive patients with reactivation of latent cytomegalovirus (CMV) infection during immunosuppressive therapy. The test proved sufficiently sensitive to detect in the blood of both patients a temporary expansion of CD8 + T lymphocytes reactive with a known immunogenic HLA-A2.1-binding peptide from glycoprotein B of CMV. Reactivity to peptide antigens was not only reflected by numeric increases of spot formation, but also by the appearance of larger spot areas, presumably formed by strongly peptide-reactive CD8 + T cells. We conclude that the combined use of the TNF- α ELISPOT assay and CVIA allows reliable monitoring of the T cell responsiveness to peptide antigens in peripheral blood.

Functional properties of neurons in macaque area V3.

We investigated the functional properties of neurons in extrastriate area V3. V3 receives inputs from both magno- and parvocellular pathways and has prominent projections to both the middle temporal area (area MT) and V4. It may therefore represent an important site for integration and transformation of visual signals. We recorded the activity of single units representing the central 10 degrees in anesthetized, paralyzed macaque monkeys. We measured each cell's spatial, temporal, chromatic, and motion properties with the use of a variety of stimuli. Results were compared with measurements made in V2 neurons at similar eccentricities. Similar to area V2, most of the neurons in our sample (80%) were orientation selective, and the distribution of orientation bandwidths was similar to that found in V2. Neurons in V3 preferred lower spatial and higher temporal frequencies than V2 neurons. Contrast thresholds of V3 neurons were extremely low. Achromatic contrast sensitivity was much higher than in V2, and similar to that found in MT. About 40% of all neurons showed strong directional selectivity. We did not find strongly directional cells in layer 4 of V3, the layer in which the bulk of V1 and V2 inputs terminate. This property seems to be developed within area V3. An analysis of the responses of directionally selective cells to plaid patterns showed that in area V3, as in MT and unlike in V1 and V2, there exist cells sensitive to the motion of the plaid pattern rather than to that of the components. The exact proportion of cells classified as being selective to color depended to a large degree on the experiment and on the criteria used for classification. With the use of the same conditions as in a previous study of V2 cells, we found as many (54%) color-selective cells as in V2 (50%). Furthermore, the responses of V3 cells to colored sinusoidal gratings were well described by a linear combination of cone inputs. The two subpopulations of cells responsive to color and to motion overlapped to a large extent, and we found a significant proportion of cells that gave reliable and directional responses to drifting isoluminant gratings. Our results show that there is a significant interaction between color and motion processing in area V3, and that V3 cells exhibit the more complex motion properties typically observed at later stages of visual processing.

T cell clones to epitopes of glutamic acid decarboxylase 65 raised from normal subjects and patients with insulin-dependent diabetes.

Insulin-dependent diabetes (IDDM) is probably mediated by T lymphocytes recognizing critical beta cell autoantigens. Glutamic acid decarboxylase (GAD) 65 is a major antigen in IDDM. T cells in both IDDM patients and controls respond to GAD 65 and certain epitopes of this molecule. To clarify the immune response to GAD 65 we established T cell clones specifically recognizing epitopes of GAD 65. We obtained T cells clones to GAD 65 peptides 161-175 (from a healthy individual), and 505-519 and 521-535 (from two IDDM patients). On extensive screening T cells responsive to peptide 161-175 were found only in controls, while T cells responsive to peptide 521-535 were found only in IDDM patients; T cells from both IDDM patients and controls responded to peptide 505-519. We could exclude simple genetic shaping of these T cell responses since the responses differed between genetically identical twins discordant for IDDM. Reactivity of T cell clones from the control to peptide 161-175 was restricted by HLA DR1 but promiscuous for HLA DR4 as DR4+ EBV transformed B cells and DR4+ mouse L-transfectants could present the peptide. As DR4+ antigen presenting cells of diabetics could present peptide 161-175 to some clones, the lack of response to this epitope in diabetic patients cannot be due to inadequate antigen presentation but is probably due to deletion of these cells either centrally or peripherally. Reactivity of clones to peptide 505-519 was either HLA DR1 or DQ1 restricted. In conclusion, T cell clones to specific epitopes of GAD 65 provide a model to clarify those differences in the immune response to this autoantigen between controls and IDDM patients.

C-kit ligand (SCF) in human multiple myeloma cells.

Here we review our recent experience addressing the role of SCF in multiple myeloma (MM). We first investigated the proliferation of MM cell lines and bone marrow samples from myeloma patients in response to rh-SCF alone and combined with Interleukin-6 (IL-6), IL-3, and IL-3/GM-CSF fusion protein PIXY 321. Neoplastic plasma cells were highly purified (>90%) by immunomagnetic depletion of T, myeloid, monocytoid and NK cells. The number of S-phase cells was evaluated after 3 days of liquid culture by the bromodeoxyuridine (BRDU) incorporation assay. The proliferation of RPMI 8226 and U266 cell lines was also assessed by a clonogenic assay. All the experiments were performed in serum-free conditions. RPMI 8226 cell line was not stimulated by SCF which also did not augment the proliferative activity of IL-6, IL-3 and PIXY-321. Conversely, SCF addition resulted in 2.4-fold increase of the number of U266 colonies and in a higher number of U266 and MT3 cells in S-phase. The c-kit ligand also enhanced the proliferation of MT3 and U266 cells mediated by the other cytokines. Anti-SCF polyclonal antibodies completely abrogated the proliferative response of MT3 cells to exogenous SCF and markedly reduced the spontaneous growth of the same cell line. Reverse transcriptase-polymerase chain reaction amplification (RT-PCR) did detect SCF mRNA in MT3 and RPMI 8226 cells. Moreover, secreted SCF was found, in a biologically active form, in the supernatant of the two cell lines by the MO7e proliferation assay. These results suggest that an autocrine proliferative loop may be operative in MT3 cell line. When tested on fresh myeloma samples, SCF increased the number of S-phase plasma cells (4.7 +/- 1.6% vs 3.4 +/- 1.3% in control cultures; p = 0.02). Significant proliferation was also induced by IL6, IL-3 and PIXY-321. The addition of SCF significantly enhanced the proliferation of myeloma cells responsive to IL-6. Preliminary experiments performed on circulating plasma cells and myeloma precursors further supported the role of SCF on the proliferation of the neoplastic clone in MM.

The B-cell response in lymphoid tissue of mice immunized with various antigenic forms of the influenza virus hemagglutinin

Protection of BALB/c (H-2d) mice against secondary challenge with influenza A viruses is primarily dependent on appropriate recognition of the hemagglutinin (HA) molecule by effectors of humoral immunity, the B lymphocytes and their product the immunoglobulin molecules. The influence of the antigenic form of the HA in eliciting protective antibodies is not clearly defined. We directly monitored the kinetics, character, localization, and helper T-cell dependence of the primary antibody-forming cell (AFC) response and the development of B-cell memory in lymphoid tissues associated with the upper and lower respiratory tracts, and in the spleen and bone marrow, to three forms of HA with various degrees of antigenic organization. Our results show that the antigenic organization of HA substantially influences B-cell immunity, namely, the capacity to generate both primary AFCs and memory B cells responsive to lethal challenge. Immunization by infection is the most efficient means of generating protective memory B cells, in contrast to subunit vaccine. The data also indicate that memory AFCs are predominantly localized to the regional lymphoid tissue where challenge HA is found, unlike primary AFCs, which are restricted to the priming site and which require in vivo CD4+ T-cell help.

Genetic and physiologic modulation of the prestarvation response in Dictyostelium discoideum.

Throughout vegetative growth, Dictyostelium amoebae secrete an autocrine factor, prestarvation factor, PSF, which accumulates in proportion to cell density. During late exponential growth, PSF induces the expression of several genes whose products are needed for cAMP signaling and cell aggregation. Among these genes are discoidin-I and the 2.4-kb transcript of cyclic nucleotide phosphodiesterase (PDE). We have identified several parameters that modulate expression of one or both of these prestarvation response genes; all effects were monitored in cells growing exponentially on bacteria. Under these conditions, axenic mutants produce higher levels of PSF activity than wild-type cells. Consistent with the high PSF levels, the 2.4-kb PDE transcript is more abundant in axenic strains than wild-type cells at the same cell density. In contrast, the density-dependent induction of discoidin-I is greatly delayed in axenic strains, occurring only at the very end of exponential growth. Analysis of axenic strains of independent origin suggested that this negative effect on discoidin-I expression is attributable to the axenic mutations themselves. The effects of two environmental factors that inhibit the prestarvation response (the bacteria upon which the cells feed and a bacterial product, folic acid) were also analyzed. We found that folate does not account for the inhibitory effect of bacteria. Cells deficient in the G-protein beta subunit, which is thought to be common to all heterotrimeric G-proteins in Dictyostelium, respond to PSF in the same manner as G beta+ cells, and this response is inhibited by bacteria. However, folate has no inhibitory effect on g beta- cells, indicating that folate inhibition is mediated by a heterotrimeric G-protein. In cells lacking the catalytic subunit of protein kinase A, the prestarvation response is severely impaired, but about 3% of the pka- cells manifest an apparently normal density-dependent induction of discoidin-I. This behavior and the heterogeneity of the prestarvation response in wild-type cells lead us to speculate that protein kinase A may not be required for PSF signal transduction per se, but rather may render the cells responsive to PSF. Based on analysis of adenylyl cyclase mutants (aca-), the effect of protein kinase A is not cAMP-dependent.

Expression and functional role of c-kit ligand (SCF) in human multiple myeloma cells.

In this study we investigated the proliferation of three well-documented MM lines and 10 bone marrow samples from myeloma patients in response to rh-SCF alone and combined with Interleukin-6 (IL-6), IL-3 and IL-3/GM-CSF fusion protein PIXY 321. Neoplastic plasma cells were highly purified (> 90%) by immunomagnetic depletion of T, myeloid, monocytoid and NK cells. The number of S-phase cells was evaluated after 3 and 7 d of liquid culture by the bromodeoxyuridine (BRDU) incorporation assay. The proliferation of RPMI 8226 and U266 cell lines was also assessed by a clonogenic assay. All the experiments were performed in serum-free conditions. RPMI 8226 cell line was not stimulated by SCF which also did not augment the proliferative activity of IL-6, IL-3 and PIXY-321. Conversely, SCF addition resulted in 2.4-fold increase of the number of U266 colonies and in a higher number of U266 and MT3 cells in S-phase (24.5 +/- 2% SEM v 14.5 +/- 1% SEM and 32 +/- 3% SEM v 21 +/- 4% SEM, respectively; P < 0.05). The c-kit ligand also enhanced the proliferation of MT3 and U266 cells mediated by the other cytokines. Anti-SCF polyclonal antibodies completely abrogated the proliferative response of MT3 cells to exogenous SCF and markedly reduced the spontaneous growth of the same cell line. Reverse transcriptase-polymerase chain reaction amplification (RT-PCR) did detect SCF mRNA in MT3 and RPMI 8226 cells. Moreover, secreted SCF was found, in a biologically active form, in the supernatant of the two cell lines by the MO7e proliferation assay. When tested on fresh myeloma samples, SCF increased the number of S-phase plasma cells (4.7 +/- 1.6% v 3.4 +/- 1.3% in control cultures: P = 0.02). Significant proliferation was also induced by IL-6 (7 +/- 2.3% of BRDU+ cells; P = 0.006), IL-3 (5.3 +/- 1.3%; P = 0.01) and PIXY-321 (5.4 +/- 1.6%; P = 0.02). The addition of SCF significantly enhanced the proliferation of myeloma cells responsive to IL-6. In summary, our results indicate that SCF is expressed in MM cells and stimulates the proliferation of neoplastic plasma cells.

Olfactory receptor cell responses ofIps grandicollis (eichhoff) (Coleoptera: Scolytidae) to intra- and interspecific behavioral chemicals

Electrophysiological recordings from antennal olfactory receptor cells were obtained fromIps grandicollis. Recordings were made from olfactory receptor cells from nine regions of the antennae in response to stimulation with the semiochemicalsα-pinene, frontalin,endo-brevicomin, verbenone,trans-verbenol,cis-verbenol, ipsdienol, and ipsenol. In many cases, up to two cells were recorded concurrently from the same location. When compared to males, females had a greater percentage of cells responsive to the primary pheromones ofDendroctonus frontalis, frontalin andtrans-verbenol, and ofIps spp., ipsdienol and ipsenol. Among females, more cells responded totrans-verbenol and theIps-produced volatiles than to host or otherD. frontalis-produced compounds. Olfactory cells of males responded mostly tocis-verbenol, followed byα-pinene, verbenone,trans-verbenol, andendo-brevicomin. Of those cells responsive primarily to one compound, the greatest percentage were responsive totrans-verbenol in females and to verbenone in males. The response of the antennal olfactory receptor cells to semiochemicals used by male and femaleI. grandicollis is consistent with the presence of these compounds during the host colonization period for each sex. Our results, which show a lack of specificity in most pheromone and host odor receptor cells, is in contrast with previously published accounts of olfactory receptor cell specificity in otherIps species.

Limiting dilution analysis of interleukin‐2‐producing T cells responsive to recall and alloantigens in human immunodeficiency virus‐infected and uninfected individuals

Peripheral blood mononuclear cells (PBMC) from individuals who were seropositive for the human immunodeficiency virus type 1 (HIV), and most without symptoms (HIV+) were compared with PBMC from healthy HIV-seronegative (HIV-) individuals for in vitro generated T helper cell (Th) responses. Th function in bulk culture and limiting dilution analysis was assessed by IL-2 production following stimulation with influenza A virus (FLU) or irradiated allogeneic PBMC (ALLO). We observed that the frequencies of FLU- and ALLO-stimulated Th cells were not appreciably different in the PBMC of HIV- individuals, and that they were also not different in the PBMC of those HIV+ individuals who responded to both FLU and ALLO in bulk culture. However, there was a severe drop in the Th frequency to FLU in HIV+ individuals who were unresponsive to FLU but responsive to ALLO by bulk culture. The PBMC of HIV+ individuals who were unresponsive by bulk culture to both FLU and ALLO exhibited a drastic reduction in the Th frequencies for both stimuli. These results demonstrate a concordance between Th functional analysis performed by limiting dilution and bulk culture. The results also indicate that the early selective loss in Th function to recall antigens is not likely to be due simply to a difference in frequencies of FLU- and ALLO-stimulated Th cells present prior to the onset of Th dysfunction.

Time course of neural responses discriminating different views of the face and head.

1. Measurements of the magnitude and time course of response were made from 44 cells responsive to static head views at different levels of stimulus effectiveness. In this way responses to complex stimulus patterns evoking good, poor, and midrange responses could be compared across the cell population. 2. Cells exhibiting both good and poor initial discrimination between head views were found at short and long latencies; there was no correlation of any of the temporal response parameters measured with cell response latency. 3. The time course of the population response to the most effective stimuli showed a rapid increase to a peak firing rate (onset to peak, rise time, 58 ms) that was on average 115 spikes/s above spontaneous activity (S/A), followed by slower decay (decay time, 93 ms) to a maintained discharge rate (15% of the peak rate above S/A). 4. Discrimination between responses to different head views exhibited by the population showed a sharp rise and reached highly significant levels within 25 ms after the population's response onset. 5. On average, activity in a single neuron (the Average Cell) rises to 44% of its peak response rate within 5 ms of the response onset. 6. The Average Cell also showed exceptionally fast discrimination between views, significant within 5 ms of response onset. 7. It is argued that the fast rise in firing rate, followed by a decay to a lower rate and the very fast emergence of discrimination are features of pattern processing present in real neural systems that are lacking in many processing models based on artificial networks of neuronlike elements, particularly those where discrimination relies on top-down and/or lateral competitive inhibition. 8. It is concluded that the only way to account for the rapid discrimination is to consider a coding system in which the first spike from multiple sources is used to transmit information between stages of processing.

Influence of T cell receptor V alpha expression on Mlsa superantigen-specific T cell responses.

Recognition of conventional foreign antigen by T cells is determined by the expression of multiple variable regions of both alpha and beta chains of the T cell receptor (TCR) alpha/beta heterodimer. In contrast, there exists a class of antigens that appears to interact with the TCR alpha/beta heterodimer through the variable region on the beta chain (V beta), independent of other TCR components, a property that has led to their designation as superantigens. The goal of the present study was to analyze V alpha use in V beta 6+ T cells responsive to the superantigen, Mlaa. Results indicate that while deletion of T cells expressing V beta 6 in Mlsa-expressing mice is essentially complete and therefore appears to occur regardless of V alpha usage, in vitro Mlsa stimulation of T cells from Mlsa-negative mice results in significant skewing of V alpha use among responding V beta 6+ T cells. This indicates that V alpha expression influences recognition of the superantigen, Mlsa by mature peripheral T cells.

'Natural' T cells responsive to malaria: evidence implicating immunological cross-reactivity in the maintenance of TCR alpha beta+ malaria-specific responses from non-exposed donors.

It is now generally accepted that peripheral blood of humans not exposed previously to malaria contains T cells which proliferate vigorously in response to malaria parasites and antigens. Although it has been claimed that these cells express a memory phenotype, their origin is uncertain. We have examined the phenotype and immunological responses of such cells. We confirm that these cells do express the 'memory phenotype', CD45Ro, in that depletion of such cells, but not of CD45Ra (virgin) cells, abrogates the immune response to malaria parasites. In an effort to define the genesis of these responses, numerous malaria-specific T cell clones have been generated from non-exposed individuals. These were tested for reactivity to a large panel of common bacterial, viral, and fungal pathogenic and non-pathogenic organisms. Most clones proliferated vigorously in response to one or more such organisms, while many clones demonstrated smaller but significant degrees of proliferation in response to many different organisms. Our data offers insights into the maintenance of immunological memory. All clones examined were CD3+, CD4+, CD8-, TCR alpha beta+, and TCR delta-. The ratio of TCR alpha beta+ to TCR delta+ cells among peripheral blood lymphocytes increased during polyclonal culture in the presence of parasite. The high frequency of such cells in peripheral blood (1/800-1/9000), and their response to a wide range of geographically different Plasmodium falciparum isolates and clones by both proliferation and lymphokine secretion (predominantly IFN-gamma) with a high degree of sensitivity (less than 1 parasite/microliters blood in some cases) suggests that these cells must be quickly activated following malaria infection. Their contribution to the outcome of the disease (protection/immunopathology) may be significant.

Induction of interleukin-5 responsiveness in resting B cells by engagement of the antigen receptor and perception of a second polyclonal activation signal

Experiments were performed to examine the nature of agents which could induce IL-5 responsiveness in small, resting splenic B lymphocytes. First, IL-5 increased plaque forming cell responses to the TI-1 antigen TNP-LPS. A second set of experiments using anti-IgM + LPS which allowed limiting dilution analysis showed induction of IL-5 responsiveness in about 20% of the resting B cell population. In the same system, IL-4 increased the percentage of proliferating cells by about 40%. A third system using the TI-2 analog conjugate anti-IgD-dextran (anti-δ-dextran) also rendered small, resting B cells responsive to IL-5. An additional system employing anti-IgM plus dextran sulfate, which also allowed limiting dilution analysis, induced IL-5 responsiveness in at least 10% of resting B cells. The features common to all four systems inducing B cell IL-5 responsiveness are at least twofold. Each system directly accesses the B cell antigen receptor and causes crosslinking. Second, each system also provides an additional polyclonal activating moiety, some of which may be similar to those in thymus independent antigens. These results suggest that some resting B cells may become IL-5 receptive after perception of at least two kinds of signals one of which perturbs sIg and the second being nonspecific and polyclonally activating.

A quantitative analysis of pallidal discharge during targeted reaching movement in the monkey

Neurons in the globus pallidus have been studied during reaching movements of the arm made at varying speeds. The reaching task is similar to one used in earlier experiments, in which disruption of normal pallidal output caused changes in movement time. The pallidal cells studied were those that showed task-related changes in activity and a modification of discharge when the arm was manipulated outside of the task. Neuronal discharge was assessed to evaluate two possible models, one in which the timing of task-related discharge varied as a function of movement time and the other in which the amplitude (mean firing rate) of the change in discharge varied as movement time varied. The relation between neuronal discharge and movement time was examined quantitatively on a trial-by-trial basis using a statistical algorithm that identified each phase of the change in neuronal discharge on each trial. A non-parametric statistic was used to determine the correlation between movement time and the duration or latency of changes in neural firing or the mean discharge during each phase of the cell's response. For fifty-five percent of the 40 neurons studied, the timing of the cell's response (duration or latency) varied as a function of movement time. For only 10 cells (25%) was there a significant correlation between movement time and the mean firing rate during one or more phases of the cell's response. Both timing and frequency modulation with movement time were limited to cells responsive to manipulation at the wrist or the shoulder.

Tumor necrosis factor-alpha inhibits the competence signal delivered by HIV to normal B cells.

Polyclonal B cell activation is commonly observed in HIV-infected patients. The coordinate delivery of a number of signals is required for B cell response. This work was designed to better define the role of HIV in the first steps of normal human B cells activation. We show that the infectious virus or recombinant envelope proteins can render B cells responsive to the growth-promoting effect of several T cell-derived IL, IL-2, IL-4, and low m.w. (12-kDa) BCGF. HIV acts in the absence of monocytes and on different populations of B cells. The competence signal can be provided by recombinant gp160 envelope protein. CD4 molecule is not involved in the interaction of HIV with B cells. In addition, we demonstrate that tumor necrosis factor alpha has no promoting activity when B cells are preactivated by HIV and it can suppress the response of HIV-preactivated B cells to IL-2, IL-4, and 12-kDa BCGF. Thus, the HIV envelope can deliver an early signal to normal B cells and modulate B cell response to physiologic signals. The possible relevance of this phenomenon to the immune defect observed in HIV patients is discussed.

Visual and somatosensory processing in the macaque temporal cortex: the role of ?expectation?

The somatosensory and visual properties of cells in a polymodal region of temporal cortex were studied in 4 awake behaving macaque monkeys. When stimulated passively and out of sight, cells with tactile responses were found to have very large receptive fields covering most of the body surface and an apparent lack of selectivity for size, shape or texture of the tactile stimulus. These properties are equivalent to those described for the anaesthetized preparation (Bruce et al. 1981). Our study revealed that tactile responses were influenced by the degree to which stimuli could be 'expected'. Tactile stimulation arising from active exploration of novel surfaces produced vigourous neuronal responses but equivalent stimulation of the skin arising when the monkey contacted 'expected' surfaces such as itself or items with which it had become familiar produced no responses. The responses of cells to active or passive tactile stimulation were attenuated when the monkey could see the objects causing the stimulation. For cells responsive to more than one sensory modality, visual and somatosensory responses were associated in a compatible manner. Cells responsive to the onset of touch were selective for the sight of objects moving towards the monkey, whereas cells selective for the offset of touch were responsive to the sight of movements away from the monkey.

Heterogeneity of helper/inducer T lymphocytes. IV. Stimulation of resting and activated B cells by Th1 and Th2 clones.

To test the hypothesis that resting and previously activated B lymphocytes differ in their proliferative and differentiative responses to various Th cell-derived stimuli, we have examined the interactions of purified small (resting) and large (activated) murine B cells with rabbit Ig-specific Th1 and Th2 clones in the presence of the Ag analogue, rabbit anti-mouse Ig antibody. Small numbers of Th2 cells induce strong Ag-dependent proliferation of and Ig secretion by both resting and activated B lymphocytes. In contrast, Th1 clones stimulate lower responses of activated B cells and fail to stimulate small resting B cells. An interaction with Th1 clones does make small B cells responsive to the Th2-derived cytokine, IL-4, indicating that Th1 clones are capable of delivering some but not all the stimuli necessary for the induction of humoral immunity. Finally, in order to compare the responses of small and large B cells to cognate interactions and secreted cytokines, we used an autoreactive I-Ak-specific Th2 line. This line induces proliferation of and Ig secretion by I-Ak expressing but not H-2d resting and activated B cells as a result of cognate interactions. However, when the H-2d B cells are bystanders in the presence of cytokine secretion by this Th2 line, or are directly exposed to Th2-derived cytokines, both small and large B cells are induced to proliferate but only the large B cells secrete antibody. These results indicate that the magnitude and nature of antibody responses depend on three principal factors: the cytokines produced by Th cells, the state of activation of the responding B lymphocytes, and whether the B cells are recipients of cognate help or are bystanders at the site of T cell stimulation. Our findings also confirm the view that cognate T-B interactions are most efficient for initiating B cell responses and may allow B cells to subsequently respond to a variety of T cell-derived cytokines.

The T cell repertoire to a multideterminant antigen. Clonal heterogeneity of the T cell response, variation between syngeneic individuals, and in vitro selection of T cell specificities.

The specificity of lysozyme-induced T cell proliferative responses by individual B10.A mice was compared by using a panel of three peptides. A surprising degree of variation in the focus of the responses was observed among individual animals, both in the newly isolated lymph node cell populations and in long term T cell lines. The responses to each determinant after hen egg-white lysozyme immunization were not equal and in examining the mice as a group some determinants tended to be dominant. However, despite each animal favoring a restricted number of determinants, the responding T cell populations were still highly heterogeneous. The data suggest that many determinants are involved in the response to the whole Ag. The role of one or more dominant determinants can be overestimated because the degree of heterogeneity in long term T cell lines appears to be less than in freshly obtained lymph node cells, indicating that a process of in vitro selection occurs. We observed that the T cells responsive to one peptide, 46-61, appeared to have a selective advantage in vitro culture.