Patient description: The patient is a 17-year-old boy complaining of severe migratory pain in the right lower quadrant of his abdomen that started four days ago. The pain is accompanied by nausea and vomiting. He was febrile with tenderness, rebound tenderness and guarding on palpation. His WBC was elevated with dominant neutrophils. CT scan showed evidence of acute perforated appendicitis with free fluid in the pelvis. Diagnostic laparoscopy revealed phlegmon with no other abdominal abnormalities. He is now a candidate for emergent laparoscopic appendectomy under general anesthesia.

Clinical trial eligibility criteria: eligible ages (years): 2.0-999.0,  Brain Disease At the time of enrollment, subjects will: 1. Have a known or suspected infection or inflammation of the nervous system or post infection sequelae based on clinical or imaging data provided by the referral facility. For the purpose of this study, neuroinfectious disease or neuroinflammation is defined as any of the following: 1. fever with nervous system signs or symptoms (excluding delirium) 2. any neurological symptoms accompanied by cerebrospinal fluid (CSF) with evidence of inflammation (which may pleocytosis, hypoglycorrachia, elevated protein, or other evidence of intrathecal immune activation including IgG index or presence of oligoclonal bands) 3. systemic infection or inflammatory disease with neurological involvement 4. neuroimaging suggestive of infection or inflammation (for example, presence of contrast-enhancing lesions on CT or MRI) 5. clinical presentation suggestive of infection or inflammatory process of the nervous system without better explanation 6. history of infection or inflammatory process of the nervous system 2. Be willing to participate in the protocol s procedures, unless clinically contraindicated 3. Be willing to provide informed consent, either directly or via appointed legally authorized representative 4. Be willing to consent for collection of clinical data or biological samples or their cryopreservation 5. Be at least 2 years old FOR OF ONLY: At the time of enrollment, subjects will: 1. Have a known or suspected infection or inflammation of the nervous system or post infection sequelae based on clinical or imaging data provided by the referral facility. For the purpose of this study, neuroinfectious disease or neuroinflammation is defined as any of the following: 1. fever with nervous system signs or symptoms (excluding delirium) 2. any neurological symptoms accompanied by cerebrospinal fluid (CSF) with evidence of inflammation (which may pleocytosis, hypoglycorrachia, elevated protein, or other evidence of intrathecal immune activation including IgG index or presence of oligoclonal bands) 3. systemic infection or inflammatory disease with neurological involvement 4. neuroimaging suggestive of infection or inflammation (for example, presence of contrast-enhancing lesions on CT or MRI) 5. clinical presentation suggestive of infection or inflammatory process of the nervous system without better explanation 6. history of infection or inflammatory process of nervous system. 2. Be willing to provide informed consent, either directly or via appointed legally authorized representative 3. Be willing to consent for collection of clinical data or biological samples or their cryopreservation 4. Be at least 2 years old  At the time of enrollment, subjects will: 1. Not have a clinically significant medical condition that, in the best judgment of the investigators, may expose the patient to undue risk of harm or prevent the patient from completing the study (examples but are not limited to, ischemic cardiomyopathy, clotting disorder, brittle diabetes) 2. Not have an acute or unstable medical condition that, in the best judgement of the investigator, would be difficult to handle at the NIH Clinical Center 3. Not have a clearly-established diagnosis of well-characterized disease entity with validated treatment algorithms for which proposed resource investment, in the opinion of the investigators, would not contribute to further advancement of knowledge FOR OF ONLY: At the time of enrollment, subjects will not have: 1. A clearly-established diagnosis of well-characterized disease entity with validated treatment algorithms for which proposed resource investment, in the opinion of the investigators, would not contribute to further advancement of knowledge FOR 1. Have a family member enrolled on 15-N-0125 2. Be at least 2 years old 3. Be able to provide informed consent and comply with study procedures FOR 1. Not willing to consent for collection of biological samples or their cryopreservation