Purpose: We put forward a theoretical and dynamical approach for the semi-quantitative analysis of CD4+ T cell differentiation, the process by which cells with different functions are derived from activated CD4+ T naïve lymphocytes in the presence of particular cytokine microenvironments. We explore the system-level mechanisms that underlie CD4+ T plasticity-the conversion of polarized cells to phenotypes different from those originally induced.Methods: In this paper, we extend a previous study based on a Boolean network to a continuous framework. The network includes transcription factors, signaling pathways, as well as autocrine and exogenous cytokines, with interaction rules derived using fuzzy logic.Results: This approach allows us to assess the effect of relative differences in the concentrations and combinations of exogenous and endogenous cytokines, as well as of the expression levels of diverse transcription factors. We found either abrupt or gradual differentiation patterns between observed phenotypes depending on critical concentrations of single or multiple environmental cytokines. Plastic changes induced by environmental cytokines were observed in conditions of partial phenotype polarization in the T helper 1 to T helper 2 transition. On the other hand, the T helper 17 to induced regulatory T-cells transition was highly dependent on cytokine concentrations, with TGFβ playing a prime role.Conclusion: The present approach is useful to further understand the system-level mechanisms underlying observed patterns of CD4+ T differentiation and response to changing immunological challenges.

Female BALB/c mice are naturally more susceptible than males to intraperitoneal experimental infection with Taenia crassiceps metacestodes. Gonadectomy tends to equalize susceptibility between sexes by reducing in half the mean individual intensity of females and by tripling that of males. The effect of gonadectomy is seen only in mice with intact immune systems but not in irradiated mice. Purified sex hormones (17-beta estradiol, testosterone, and progesterone) do not affect cysticercus reproduction or growth in vitro. Thus, gonadal effect on mouse susceptibility to cysticercosis appears to be mediated via the immune system, and it is probably not the consequence of the major sex steroids acting directly upon the parasites. Because sublethal irradiation increases the intensity in gonadectomized females and intact males, whereas that of gonadectomized males and intact females remains unchanged, irradiation results are consistent with the hypothesis that immunological events that participate in controlling the growth of cysticerci are inhibited by ovaries and stimulated by testes.

The adaptive immune response is initiated by the interaction of the T cell antigen receptor/CD3 complex (TCR) with a cognate peptide bound to a MHC molecule. This interaction, along with the activity of co-stimulatory molecules and cytokines in the microenvironment, enables cells to proliferate and produce soluble factors that stimulate other branches of the immune response for inactivation of infectious agents. The intracellular activation signals are reinforced, amplified and diversified by a complex network of biochemical interactions, and includes the activity of molecules that modulate the activation process and stimulate the metabolic changes necessary for fulfilling the cell energy demands. We present an approach to the analysis of the main early signaling events of T cell activation by proposing a concise 46-node hybrid Boolean model of the main steps of TCR and CD28 downstream signaling, encompassing the activity of the anergy factor Ndrg1, modulation of activation by CTLA-4, and the activity of the nutrient sensor AMPK as intrinsic players of the activation process. The model generates stable states that reflect the overcoming of activation signals and induction of anergy by the expression of Ndrg1 in the absence of co-stimulation. The model also includes the induction of CTLA-4 upon activation and its competition with CD28 for binding to the co-stimulatory CD80/86 molecules, leading to stable states that reflect the activation arrest. Furthermore, the model integrates the activity of AMPK to the general pathways driving differentiation to functional cell subsets (Th1, Th2, Th17, and Treg). Thus, the network topology incorporates basic mechanism associated to activation, regulation and induction of effector cell phenotypes. The model puts forth a conceptual framework for the integration of functionally relevant processes in the analysis of the T CD4 cell function.

Objective To examine the effects of a fibronectin (FN) fragment containing the COOH‐terminal heparin‐binding domain (HBFN‐f) on chondrocyte‐mediated type II collagen (CII) cleavage by collagenase and proteoglycan (PG) degradation in articular cartilage in explant culture. Methods Intact FN or HBFN‐f was added to explant cultures of mature bovine articular cartilage. We investigated collagenase‐mediated cleavage of CII caused by HBFN‐f in explant cultures using a new immunoassay for detection and measurement of the primary collagenase cleavage site of CII. CII denaturation in cartilage was also measured using a specific enzyme‐linked immunosorbent assay. Degradation of PG (principally aggrecan) was analyzed by a dye‐binding assay. APMA and/or a matrix metalloproteinase 13 (MMP‐13) preferential inhibitor or interleukin‐1 receptor antagonist (IL‐1Ra) were added to some cultures to examine the presence of latent procollagenase or the involvement of MMP‐13 or IL‐1, respectively, in cartilage breakdown induced by HBFN‐f. Secretion of MMP‐3 and MMP‐13 into media was detected by immunoblotting. Results In contrast to intact FN, HBFN‐f was shown to stimulate CII cleavage by collagenase in a dose‐dependent manner following PG degradation, similar to cartilage breakdown induced by IL‐1. Treatment with HBFN‐f also resulted in elevated denaturation of CII. Immunoblotting demonstrated that HBFN‐f enhanced pro–matrix metalloproteinase 13 (proMMP‐13) production as well as that of proMMP‐3. APMA, which activates latent proMMPs, enhanced the HBFN‐f–mediated cleavage of CII by collagenase. An MMP‐13 preferential inhibitor or IL‐1Ra suppressed HBFN‐f–induced collagen cleavage to control levels. Conclusion Our data demonstrate that HBFN‐f can induce early PG degradation and subsequent CII cleavage. The latter is probably mediated by early proMMP‐13 induction involving an IL‐1–dependent pathway. Activation of latent collagenase is delayed. This new information, together with existing data on other FN fragments, reveals that increased levels of these fragments, found in diseased joints such as in osteoarthritis and rheumatoid arthritis, may stimulate cartilage breakdown by mechanisms of the kind demonstrated in the present study.

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