Agent-based vs. equation-based multi-scale modeling for macrophage polarization.

Macrophages show high plasticity and result in heterogenic subpopulations or polarized states identified by specific cellular markers. These immune cells are typically characterized as pro-inflammatory, or classically activated M1, and anti-inflammatory, or alternatively activated M2. However, a more precise definition places them along a spectrum of activation where they may exhibit a number of pro- or anti-inflammatory roles. To understand M1-M2 dynamics in the context of a localized response and explore the results of different mathematical modeling approaches based on the same biology, we utilized two different modeling techniques, ordinary differential equation (ODE) modeling and agent-based modeling (ABM), to simulate the spectrum of macrophage activation to general pro- and anti-inflammatory stimuli on an individual and multi-cell level. The ODE model includes two hallmark pro- and anti-inflammatory signaling pathways and the ABM incorporates similar M1-M2 dynamics but in a spatio-temporal platform. Both models link molecular signaling with cellular-level dynamics. We then performed simulations with various initial conditions to replicate different experimental setups. Similar results were observed in both models after tuning to a common calibrating experiment. Comparing the two models' results sheds light on the important features of each modeling approach. When more data is available these features can be considered when choosing techniques to best fit the needs of the modeler and application.

Thyroid Autoimmunity: An Interplay of Factors.

The literature on thyroid autoimmunity has identified many potential factors at play for the initiation and progression of autoimmune thyroid diseases. These factors include genetic susceptibility, environmental factors, some drugs, iodine and selenium, infection, molecular mimics, and immune system defects. The sheer number of feasible factors makes sorting out the necessary agents from the fellow travelers difficult. In addition, many of these factors have the capability to interact-further confusing the picture. Another difficulty in interpreting these data is that most proposed mechanisms are not able to accomplish the triggering event in which the tolerance to self-antigens is actually overcome. In addition, some findings may be describing the conditions present after a disease is diagnosed and may be consequences of the disease rather than a cause. Recent description of the role of adipokines, which include leptin, tumor necrosis factor-alpha, and interleukin-6, in contributing to the inflammatory environment of the thyroid, along with the presence of thyroid Toll-like receptors for pathogen-associated patterns have the potential to deliver that necessary adjuvant signal to break tolerance, seen as necessary in animal autoimmune models. An additional factor, vitamin D3, due to its interaction both with white adipose tissue (WAT) and the immune system, has a complicated and somewhat controversial story with respect to thyroid autoimmunity. Conflicting results can result when not all factors are considered together. AIMS: To describe the many factors at play in thyroid autoimmunity and how they interact. CONCLUSION: Thyroid autoimmunity is the result of an interplay of factors, with adipokines produced by WAT and vitamin D providing immune modulating signals external to the thyroid, while thyrocyte innate responses to environmental conditions provide the necessary adjuvant signal. Shaping the response to be reactive to particular self-antigens and likelihood of a response are due to genetics and molecular mimics.