1,877 research outputs found
Immunological tolerance: Danger – pathogen on the premises!
AbstractRecent results show that immune responses can be induced in neonatal mice. Do they really refute the traditional view that the ability to discriminate between ‘self’ and ‘non-self’ is a fundamental property of the immune system
Inferring processes underlying B-cell repertoire diversity
We quantify the VDJ recombination and somatic hypermutation processes in
human B-cells using probabilistic inference methods on high-throughput DNA
sequence repertoires of human B-cell receptor heavy chains. Our analysis
captures the statistical properties of the naive repertoire, first after its
initial generation via VDJ recombination and then after selection for
functionality. We also infer statistical properties of the somatic
hypermutation machinery (exclusive of subsequent effects of selection). Our
main results are the following: the B-cell repertoire is substantially more
diverse than T-cell repertoires, due to longer junctional insertions; sequences
that pass initial selection are distinguished by having a higher probability of
being generated in a VDJ recombination event; somatic hypermutations have a
non-uniform distribution along the V gene that is well explained by an
independent site model for the sequence context around the hypermutation site.Comment: acknowledgement adde
Statistical mechanics of clonal expansion in lymphocyte networks modelled with slow and fast variables
We study the Langevin dynamics of the adaptive immune system, modelled by a
lymphocyte network in which the B cells are interacting with the T cells and
antigen. We assume that B clones and T clones are evolving in different thermal
noise environments and on different timescales. We derive stationary
distributions and use statistical mechanics to study clonal expansion of B
clones in this model when the B and T clone sizes are assumed to be the slow
and fast variables respectively and vice versa. We derive distributions of B
clone sizes and use general properties of ferromagnetic systems to predict
characteristics of these distributions, such as the average B cell
concentration, in some regimes where T cells can be modelled as binary
variables. This analysis is independent of network topologies and its results
are qualitatively consistent with experimental observations. In order to obtain
full distributions we assume that the network topologies are random and locally
equivalent to trees. The latter allows us to employ the Bethe-Peierls approach
and to develop a theoretical framework which can be used to predict the
distributions of B clone sizes. As an example we use this theory to compute
distributions for the models of immune system defined on random regular
networks.Comment: A more recent version (accepted for publication in Journal of Physics
A: Mathematical and Theoretical) with improved figures, references, et
A Multi-Scale Model for Correlation in B Cell VDJ Usage of Zebrafish
The zebrafish (\emph{Danio rerio}) is one of the model animals for study of
immunology because the dynamics in the adaptive immune system of zebrafish are
similar to that in higher animals. In this work, we built a multi-scale model
to simulate the dynamics of B cells in the primary and secondary immune
responses of zebrafish. We use this model to explain the reported correlation
between VDJ usage of B cell repertoires in individual zebrafish. We use a delay
ordinary differential equation (ODE) system to model the immune responses in
the 6-month lifespan of a zebrafish. This mean field theory gives the number of
high affinity B cells as a function of time during an infection. The sequences
of those B cells are then taken from a distribution calculated by a
"microscopic" random energy model. This generalized model shows that
mature B cells specific to one antigen largely possess a single VDJ
recombination. The model allows first-principles calculation of the
probability, , that two zebrafish responding to the same antigen will select
the same VDJ recombination. This probability increases with the B cell
population size and the B cell selection intensity. The probability
decreases with the B cell hypermutation rate. The multi-scale model predicts
correlations in the immune system of the zebrafish that are highly similar to
that from experiment.Comment: 29 pages, 10 figures, 1 tabl
Parallel processing in immune networks
In this work we adopt a statistical mechanics approach to investigate basic,
systemic features exhibited by adaptive immune systems. The lymphocyte network
made by B-cells and T-cells is modeled by a bipartite spin-glass, where,
following biological prescriptions, links connecting B-cells and T-cells are
sparse. Interestingly, the dilution performed on links is shown to make the
system able to orchestrate parallel strategies to fight several pathogens at
the same time; this multitasking capability constitutes a remarkable, key
property of immune systems as multiple antigens are always present within the
host. We also define the stochastic process ruling the temporal evolution of
lymphocyte activity, and show its relaxation toward an equilibrium measure
allowing statistical mechanics investigations. Analytical results are compared
with Monte Carlo simulations and signal-to-noise outcomes showing overall
excellent agreement. Finally, within our model, a rationale for the
experimentally well-evidenced correlation between lymphocytosis and
autoimmunity is achieved; this sheds further light on the systemic features
exhibited by immune networks.Comment: 21 pages, 9 figures; to appear in Phys. Rev.
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