Navegando por Autor "Santos, Rita Maria Zorzenon dos"
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Item Immune network at the edge of chaos.(1997) Bernardes, Américo Tristão; Santos, Rita Maria Zorzenon dosSome time ago Jerne proposed a new theory to explain the basis of the behaviour of the immune system. He suggested the existence of a functional connected network, based on pattern recognition of the idiotypes carried by the lymphocytes, which is responsible for the self regulation of the immune system. Only 04 19) of the lymphocytes available in the immune repertoire will participate in this functional network, while the rest of the lymphocytes will be free to respond to any foreign antigen. Each individual immune repertoire will be different depending on the lymphocytes that participate in the connected network. Using a very simple cellular automata model of the immune repertoire dynamics we show that, although the usual regimes "stable and chaotic# attained by this automata, are not interesting from the biological point of view, the transition region, at the edge of chaos, is very appropriate to describe such dynamics[ In this region we have obtained a functional connected network involving 09 19) of the lymphocytes available in the repertoire, as suggested by Jerne and others[ The model also reproduces the immune system signature, the ensemble of different lymphocytes that each individual expresses in his immune repertoire, which varies from one individual to another[ We show how the immune memory comes out as a consequence of the dynamics of the system[ From our results we confirm and present evidence that the chaotic regime corresponds to a sort of non- healthy state, as has been suggested previously.Item Immunization and aging : a learning process in the immune network.(1998) Bernardes, Américo Tristão; Santos, Rita Maria Zorzenon dosImmunization and aging: a learning process in the immune network. The immune system can be thought as a complex network of different interacting elements. A cellular automaton , defined in shape- space, was recently shown t o exhibit self- regulation an d complex behavior an d is, therefore, a good candidate t o model the immune system . Using this model t o simulate a real immune system we find good agreement with recent experiments on mice. The model exhibits the experimentally ob served refractory behavior of the immune system under multiple antigen present at ion s as well as loss of it s plasticity caused by aging.Item The stable-chaotic transition on cellular automata used to model the immune repertoire.(1995) Santos, Rita Maria Zorzenon dos; Bernardes, Américo TristãoIn this paper we study a simplified version of the cellular automata approximation introduced by De Boer, Segel and Perelson to model the immune repertoire. The automaton rule defines an activation window based on the idea of the proliferation function (biphasic dose-response function), which is used to describe the receptor crosslinking involved in the B cell activation. This proliferation function is very sensitive to the activation threshold and activation interval definitions. Here we investigate the influence of these parameters on the automaton rule proposed by Stauffer and Weisbuch. Using a fixed window they obtained the stable-"chaofic" transition only for d > 4. We find, contrary to their results, that this transition is always present for d > 2 until a certain critical value of the activation threshold is attained, above which this transition disappears and the system will always evolve towards a stable configuration. The shorter the activation interval the faster the system undergoes to the "chaotic" behaviour. Increasing the activation interval there is a certain critical size from which the system will always exhibit the same behaviour no matter the activation interval size. We also investigate the influence of the initial distribution on the results. Since we defined the relevant parameters of the model, we obtained the phase diagrams exhibiting the regions of stable and "chaotic" behavior. Such diagrams are not easily found in the literature.