Recently, an interaction between neurodegenerative processes and the innate and adaptive immune responses has been increasingly recognized. Activation of microglia, infiltration of peripheral T lymphocytes, and T-cell interaction with microglia may strongly affect the progression of Parkinson's disease (PD) both in patients and in animal models of the disease. Here, we summarize the current knowledge regarding the role of microglia in the progression of PD. The plasticity of the microglial response is also discussed in the context of PD. In addition, we also focus on the influence of several peripheral T-cell subsets on PD progression as well as on possible pathways by which they might act. This review should help increase our understanding of the effects of innate and adaptive immune cells in the pathogenesis of PD.