  We formulate a model of a semiconductor Quantum Dot laser with injection of
spin-polarized electrons. As compared to higher-dimensionality structures, the
Quantum-Dot-based active region is known to improve laser properties, including
the spin-related ones. The wetting layer, from which carriers are captured into
the active region, acts as an intermediate level that strongly influences the
lasing operation. The finite capture rate leads to an increase of lasing
thresholds, and to saturation of emitted light at higher injection. In spite of
these issues, the advantageous threshold reduction, resulting from spin
injection, can be preserved. The "spin-filtering" effect, i.e., circularly
polarized emission at even modest spin-polarization of injection, remains
present as well. Our rate-equations description allows to obtain analytical
results and provides transparent guidance for improvement of spin-lasers.
