In a previous study conducted at the University of Nebraska Medical Center (UNMC) using samples of whole blood, PD patients showed differences from caregiver controls according to results from complete blood count (CBC) with white blood cell (WBC) differential, fluorescence-activated cell sorting (FACS) analysis for T cell markers, and Treg functional assays. These immune aberrations correlated with motor dysfunction as determined by Parkinson's disease rating scale (UPDRS) part III assessments. In this pilot study, the effect of Leukine treatment on immune deficits in PD patients will be monitored. Immune cell analyses of whole blood, motor assessments, and physical examinations and blood analyses for safety, will be conducted before, during, and after Leukine or placebo treatment of PD patients, and using healthy controls during baseline data collection before drug treatment. Initially, 16 PD patients and 16 controls will be recruited. Subjects will be drawn from the previous study. Enrollment will be supplemented as needed with patients from Neurology Consultants of Nebraska-PC, UNMC Neurological Sciences, or recruitment through the American Parkinson's Disease Association. Enrollment will be staggered, and additional subjects will be recruited as needed to replace any withdrawing participants, with the goal of 32 subjects, 16 PD patients and 16 controls, completing the study.