INCLUSION CRITERIA: Be male or female, aged >18. Female participants of childbearing potential must be using a medically acceptable means of contraception. Participants must be in good general health as evidenced by medical history and physical examination. All participants must have been enrolled under UMB protocol HP-00079860 (In vivo assessment of meningeal inflammation and its clinical impact in multiple sclerosis by 7 Tesla MRI), P.I. Daniel Harrison and have agreed to contact for future research.  EXCLUSION CRITERIA:  Pregnant women. Women of childbearing potential will be screened by history for the possibility of pregnancy and undergo a urine pregnancy test Any medical contraindication to the procedures performed in the study, or any current severe medical or psychiatric illness other than MS. This includes contraindications to Celecoxib, such as aspirin sensitive asthma. Behavioral symptoms that would preclude the gathering of data for the study, or advanced disease such that subjects cannot provide assent. Clinically significant abnormalities on EKG or safety labs. MRI performed >90 days before the PET scan Subjects should not have taken NSAIDs for two weeks prior to the PET scan. Aspirin, corticosteroids, or immunosuppressants (e.g. methotrexate) must not have been taken in the prior month. Have other major neurological or medical diseases that may cause cognitive dysfunction, such as structural brain diseases, metabolic diseases, paraneoplastic syndromes, infectious diseases, or other significant neurological abnormalities. Have an unstable medical condition that, in the opinion of the investigators, makes participation unsafe (e.g., an active infection or untreated malignancy). Are unable to travel to the NIH. Have recent exposure to radiation related to research (e.g., PET from other research) that, when combined with this study, would be above the allowable limits. Have an inability to lie flat and/or lie still on the camera bed for at least two hours, including claustrophobia, overweight greater than the maximum for the scanner, and uncontrollable behavioral symptoms, which will be screened by an interview with the patient and/or caregiver during the screening visit. Be NIMH staff or an NIH employee who is a subordinate/relative/co-worker of the investigators.  Exclusion of Children  Because this protocol has more than minimal risk from radiation exposure without possibility of direct benefit, inclusion of children is not appropriate.  Exclusion of Pregnant or Breastfeeding Women  Pregnant women will be excluded because this protocol involves exposure to ionizing radiation. Lactating women will be excluded because radioisotopes may be excreted in milk.  Exclusion of Participants who are HIV Positive  Persons with HIV infection are excluded because HIV infection itself may cause neuroinflammation, and we wish to specifically study the effect of depression on neuroinflammation.  Exclusion of Participation of NIH Staff or family members of study team members  NIH staff and family members of study team members may not be enrolled in this study.