Exploratory Open Label Study for Development of a Method To Detect Dendritic Cells

Inclusion Criteria: All Healthy Subjects: * Subjects are determined by the investigator to be medically stable and expected to complete the trial as designed. * Subjects have adequate hearing, vision, and language skills to perform neuropsychiatric testing and interviews as specified in the protocol. * Subjects are able to understand and agree to comply with the study procedures and report for scheduled office visits. * Subjects are able to reliably communicate with study personnel about adverse events (AEs) and concomitant medications. * Signed written informed consent according to institutional guidelines. * Healthy Adult subjects: Male or female and between the ages of 21 to 55 inclusive. * Healthy Elderly subjects: Male or female and between the ages of 65 to 90 inclusive MMSE score \> 26. * Alzheimer's Subjects: Male or female and between the ages of 50 to 90 inclusive. Patients satisfying the criteria for the clinical diagnosis of probable AD based on National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer's Disease and Related Disorders Association (NINCDS-ADRDA). MMSE score of \> 16 and Modified Hachinski Ischemia Scale (MHIS) score of ≤ 4. Exclusion Criteria: Sex and Reproductive Status: * Women who test positive for pregnancy. * Pre-menopausal women who are not practicing two methods of birth control for 3 months prior and a week after the ICG infusion. Medical History: * Subjects with a history of any anaphylactic reactions. * Subjects with a history of allergic reaction to ICG. * Subjects with a history of iodine sensitivity and/or allergic reaction to iodine. * Subjects with a history of a clinically significant hepatic disease. Target Disease Exceptions: * Any subject diagnosed to have an autoimmune disorder. * Any subject who has any unstable cardiovascular (included uncontrolled hypertension), pulmonary, or GI disease. * For Alzheimer's patients, a medical condition other than AD that could explain or contribute significantly to the patient's dementia. Concurrent Medications: * Any subject who is immunocompromised at screening including taking medications that are systemic immunosuppressives including corticosteroids but not NSAIDS. * Any subject currently prescribed a biologic immunosuppressive therapy or having taken such therapy in the prior 3 months. Physical and Laboratory Test Findings at Screening: * Any subject with uncontrolled hypertension at screening. * Any subject with hepatic or hematological abnormalities at screening. * Any subject who has a known infection with a human immunodeficiency virus.