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The strength of T-cell receptor (TCR) stimulation and subsequent T-cell response depend on a combination of peptide-major histocompatibility complex (pMHC) density and potency. By comparing two different pMHC at doses yielding similar proliferation in vivo, we have highlighted unexpected differences in the qualitative and quantitative effects of TCR ligand. Measurements of cytokine sensitivity and two-photon imaging of T cell–dendritic cell (T–DC) interactions reveal discrimination between comparably weak stimuli resulting from either decreased pMHC potency or pMHC density. In addition, TCR-induced genes in broad gene expression profiles segregate into two groups: one that responds to cumulative TCR signal and another that responds to pMHC quality, independent of quantity. These observations suggest that models of TCR ligand discrimination must account for disparate sensitivity of downstream responses to specific influences of pMHC potency.

Variability within isogenic T cell populations yields heterogeneous ‘local’ signaling responses to shared antigenic stimuli, but responding clones may communicate ‘global’ antigen load through paracrine messengers, such as cytokines. Such coordination of individual cell responses within multicellular populations is critical for accurate collective reactions to shared environmental cues. However, cytokine production may saturate as a function of antigen input, or be dominated by the precursor frequency of antigen-specific T cells. Surprisingly, we found that T cells scale their collective output of IL-2 to total antigen input over a large dynamic range, independently of population size. Through experimental quantitation and computational modeling, we demonstrate that this scaling is enforced by an inhibitory cross-talk between antigen and IL-2 signaling, and a nonlinear acceleration of IL-2 secretion per cell. Our study reveals how time-integration of these regulatory loops within individual cell signaling generates scaled collective responses and can be leveraged for immune monitoring. DOI: http://dx.doi.org/10.7554/eLife.01944.001, eLife digest The cells of the immune system face the challenge of removing viruses and other pathogens without endangering healthy tissues. Cells called T cells plays a variety of roles in the immune response: some T cells directly destroy infected cells, some recruit other cells called phagocytes to the site of infection, and some release small proteins called cytokines. These cytokines help cells to communicate with other cells and, therefore, to tailor the overall immune responses to deal with a particular pathogen. It is known that mammals are capable of adjusting the T cell response to match the overall severity of an infection. However, it is not clear how individual T cells coordinate their seemingly binary response—they are either activated when they recognize a pathogen, or they are not activated—into a response at the collective cell level that can be varied continuously over a wide range of values. Here, Tkach et al. show that T cell populations match their production of the cytokine interleukin 2 (IL-2) to the abundance of antigens—molecules released by the pathogen—over an unexpectedly large range of concentrations. Through a combination of experimental and computational analyses, Tkach et al. identified two novel IL-2 feedback loops that help to generate the correct quantity of cytokine, irrespective of the total number of T cells. Furthermore, this model can be used to estimate antigen quantities within diseased tissues. The work of Tkach et al. illustrates the potential of feedback integration in cell signalling and gene regulation as a mechanism to allow cellular populations to respond to environmental stimuli in a graded, collective fashion. DOI: http://dx.doi.org/10.7554/eLife.01944.002

The sensitivity of T cells to interleukin-2 (IL-2) can vary by three orders of magnitude and is determined by the surface densities of the IL-2 receptor α subunits. Regulatory T cells inflict a double hit on effector T cells by lowering the bulk IL-2 concentration as well as the sensitivity of effector T cells to this crucial cytokine. This double hit deprives weakly activated effector T cells of pSTAT5 survival signals while having only minimal effects on strongly activated effector cells that express increased levels of the IL-2 receptor. Short-term signaling differences lead to a differential functional in terms of proliferation and cell division: regulatory T cell specifically suppress weakly activated effector T cells even at large numbers; small numbers of strongly activated effector T cells overcome the suppression., Self-/non-self-discrimination in the adaptive immune system relies, to a large extent, on distinctions between self-antigens and foreign antigens as made by individual T cells. As such, single-cell decisions are prone to errors a reliable immune response can be expected to incorporate further proofreading schemes. One such scheme involves long time scale, population-level interactions between effector (Teff) and regulatory (Treg) T cells. Treg cells are often described as immune suppressors; their role as immune regulators can be understood by mapping out the scenarios in which Treg suppression is either significant or insignificant. In this study, we have focused on one mechanism that allows Treg cells to suppress Teff survival, namely, interleukin-2 (IL-2) deprivation. Following antigen activation, Teff cells secrete IL-2 and express the α subunit of the IL-2 receptor (IL-2r). The binding of extracellular IL-2 to the IL-2r is crucial for Teff survival and proliferation and consequently for a full-blown immune response. Treg cells deplete this IL-2 from the environment and deprive the Teff cells of this important survival signal. In this tug-of-war for IL-2, we sought to quantitatively describe those scenarios in which IL-2 uptake by Treg cells suffices to suppress Teff cell activation and those where it does not. The core of this competition for IL-2 lies in the fact that IL-2rα is expressed on both Teff and Treg cells. To understand how IL-2 binds to its receptor, we measured IL-2r subunit levels on single cells, together with STAT5 phosphorylation as evoked by varied IL-2. Contrary to previous descriptions that set the EC50 of IL-2/IL-2r interaction at 10 pM, we found that the sensitivity of T cells to IL-2 varies over three orders of magnitude concentrations (Figure 1E, experiment). Teff cells with higher levels of IL-2rα receptor subunit are more sensitive to IL-2, Treg cells with higher levels of IL-2rα are more efficient in the scavenging of IL-2. IL-2rβ levels, on the other hand, determine response amplitudes. We describe a short time scale, two-step model to quantitatively describe IL-2 binding onto individual cells (Figure 1E, theory). IL-2r expression levels are therefore a crucial parameter for determining the outcome of the competition for IL-2. We measured the regulation of IL-2r subunits on longer time scales in cultures of either Teff or Treg cells. For both cell types, IL-2r levels depend on the exposure to IL-2. For Teff cells, there is a further dependence on the concentration of antigen by which they were activated. We then measured IL-2r expression in cocultures of Treg and Teff cells. We show how IL-2 secreted by activated Teff cells suffices in inducing IL-2rα upregulation in the Treg population. We further show that the presence of Treg cells decreased IL-2r upregulation in cocultured weakly activated Teff cells. Treg cells thus inflict a double hit on Teff cells by reducing not only extracellular IL-2 concentrations but also the Teff cells' ability to sense IL-2. Teff cells activated by high-antigen concentrations exhibit sustained IL-2rα expression that is less prone to this effect. We compared IL-2r levels on Treg cells and Teff activated by varied antigen concentrations and found a critical crossover: at low-antigen concentrations Treg cells have higher IL-2rα than Teff cells, but this is reversed at high-antigen concentrations. We constructed a long time scale computational model to quantify the significance of this crossover. The model describes IL-2/IL-2r binding and the regulation of IL-2 and IL-2r expression in populations of Treg and Teff cells. For a pure Teff population, our model predicted a ‘quorum-sensing' threshold implying that sustained pSTAT5 signaling requires a minimal concentration of cells that increases with decreasing activation strength. The model further predicts that the addition of Treg cells will greatly increase the quorum concentration for weakly activated Teff cells but have no effect on strongly activated Teff cells. We validated the model's predictions in vitro. We show a quorum-sensing threshold for activated Teff cells. We also show that the presence of a Treg population suppressed pSTAT5 signaling in a large number of weakly but has little effect on even a few strongly activated Teff cells (Figure 6C and D). On longer time scales, this translates to the suppression of cell division (Figure 6G and H) and proliferation (Figure 6I) in a manner that discriminates between strongly and weakly activated cells. We then went to demonstrate that IL-2 deprivation by Treg cells takes place in vivo. We used IL-2 injections to upregulate IL-2rα levels in Treg cells. As predicted by our in vitro results, such treatment leads to a suppressive environment in which Teff cells activated by subsequent antigen/LPS immunization proliferate to a lesser extent. We were able to reverse this suppressive effect by continuing IL-2 treatment post-immunization. This highlights IL-2 as a limiting factor for Teff proliferation and renders its scavenging by Treg cells an important mechanism of suppression in vivo. In conclusion, we formulated a quantitative description of IL-2/IL-2r regulation in mixed population of Treg and Teff cells. Population feedback loops that depend on cell numbers, molecular cell surface densities, free molecular densities and timing critically affect the outcome of the competition for IL-2. Such a description allows us to precisely identify the scenarios in which IL-2 deprivation by Treg cells has a major suppressive role in vitro and better understand the role of this mechanism in vivo., Understanding how the immune system decides between tolerance and activation by antigens requires addressing cytokine regulation as a highly dynamic process. We quantified the dynamics of interleukin-2 (IL-2) signaling in a population of T cells during an immune response by combining in silico modeling and single-cell measurements in vitro. We demonstrate that IL-2 receptor expression levels vary widely among T cells creating a large variability in the ability of the individual cells to consume, produce and participate in IL-2 signaling within the population. Our model reveals that at the population level, these heterogeneous cells are engaged in a tug-of-war for IL-2 between regulatory (Treg) and effector (Teff) T cells, whereby access to IL-2 can either increase the survival of Teff cells or the suppressive capacity of Treg cells. This tug-of-war is the mechanism enforcing, at the systems level, a core function of Treg cells, namely the specific suppression of survival signals for weakly activated Teff cells but not for strongly activated cells. Our integrated model yields quantitative, experimentally validated predictions for the manipulation of Treg suppression.

Normal human γ1A-globulin blocked passive sensitization of non-allergic humand skin with reagin. The blocking ability of the protein remained after reduction and alkulation. It was also indicated that the blocking ability was associated with A chain rather than B chain in γ1A-globulin molecules.

SUMMARY Nine patients with sickle-cell anaemia were studied by body surface counting over the spleen and liver following the injection of 51Cr-labelled red cells. In two of the patients without palpable spleens there was no excess accumulation of radioactivity over the spleen, and the spleen/liver ratio declined with time. In the remaining seven patients, all with splenomegaly, there was decreased red cell survival, an excess accumulation of radioactivity over the spleen, and an increase in the spleen/liver ratio with time, indicative of sequestration of red cells by the spleen. The significance of these findings is discussed.

Apparent Paradoxical Effects of Lanolin on Induction of Skin and Lung Tumours by Topically Applied Methylcholanthrene

Fibrinolytic activity and serum antifibrinolysin were estimated in normal pregnant women, during and after labour. The decreased fibrinolytic activity found during labour returned to non-pregnant levels within 24 hours of delivery. During the same period, the serum antifibrinolysin was rapidly diminished. It is suggested that the post-partum increase in fibrinolytic activity to non-pregnant levels is due to alterations in the fibrinolytic system itself, as well as to changes in circulating antifibrinolysin.

Actions of Cortisone on Cutaneous and Pulmonary Neoplasms Induced in Mice by Cutaneous Applications of Methylcholanthrene

PREVIOUS investigations by Trout1 and by us2 indicate clearly that the deposition of mineral in the aortae of calciferol-intoxicated rats continued long after cessation of administration of this compound and after the blood calcium-level had returned to normal. It appears that, once initiated, this process follows an irreversible course, at least in the aorta, since even 160 days after the initial insult there was no evidence of a reduction in the mineral content of the aorta. Attempts to inhibit calciferol-induced calcification of the aorta by the simultaneous administration of papain (which reduces the mucopolysaccharide content of the aorta) were unsuccessful3.