Periodic oscillations in leukopoiesis models with two delays

The term leukopoiesis describes processes leading to the production and regulation of white blood cells. It is based on stem cells differentiation and may exhibit abnormalities resulting in severe diseases, such as cyclical neutropenia and leukemias. We consider a nonlinear system of two equations, describing the evolution of a stem cell population and the resulting white blood cell population. Two delays appear in this model to describe the cell cycle duration of the stem cell population and the time required to produce white blood cells. We establish sufficient conditions for the asymptotic stability of the unique nontrivial positive steady state of the model by analysing roots of a second degree exponential polynomial characteristic equation with delay-dependent coefficients. We also prove the existence of a Hopf bifurcation which leads to periodic solutions. Numerical simulations of the model with parameter values reported in the literature demonstrate that periodic oscillations (with short and long periods) agree with observations of cyclical neutropenia in patients.     

Effects of Yersinia enterocolitica on bone marrow cells proliferation in mice

Intraperitoneal (i.p.) infection of mice with virulent Yersinia enterocolitica, that possess the virulence plasmid encoding calcium requirement, caused a significant reduction in the number of nucleated cells per femur, but increased significantly the ratio of both mitosis and in vitro colony-forming units (CFU) to marrow cells. A plasmid-less, isogenic avirulent derivative did not cause such differential effects on marrow cellularity and mitosis ratio. Thus, increase of granulocyte and mononuclear phagocyte progenitor cells by Y. enterocolitica was associated with virulence plasmid presence.