Observational StudyiMmune SignAtures and Clinical outComes in AP

Inclusion Criteria:

1. Age 18-75 years at the time of enrollment
2. Diagnosis of acute pancreatitis (AP) according to the revised Atlanta criteria (see definition below)
3. Participant is approached by the research team within 36 hours of presentation to the hospital
4. Participant fully understands and agrees to participate in all aspects of the study, including providing informed consent, completion of interviews and data forms, and collection of biospecimens

Acute pancreatitis is defined/diagnosed using the revised Atlanta criteria, which requires the presence of at least two of the following criteria:

i. Upper abdominal pain ii. Elevation of serum amylase or lipase level to >/=3 times the upper limit of normal iii. Features of AP on cross-sectional imaging.

Exclusion Criteria:

1. Diagnosis of definite chronic pancreatitis (CP) at enrollment (see also study definitions) based on either of the following criteria met by computed tomography (CT) scan (including non-contrast enhanced) or Magnetic resonance Imaging (MRI) or Magnetic Resonance Cholangiopancreatography (MRCP):

i. Parenchymal or ductal calcifications on CT scan (after excluding the possibility that calcifications are vascular) ii. Intraductal filling defects suggestive of calcifications on MRI and/or MRCP iii. Non-contrast imaging is acceptable for the assessment of definite CP, but calcifications noted by endoscopic ultrasound only (and not correlated with CT) are not considered definite CP. Patients with autoimmune pancreatitis, but no evidence of calcifications, may still be enrolled, assuming they satisfy inclusion criteria for 'diagnosis of AP'
2. Potential participants with post-ERCP AP who are expected to be hospitalized for less than 48 hours.
3. Pancreatic tumors, including ductal adenocarcinoma, neuroendocrine tumors, and metastasis.
4. Confirmed or suspected cystic tumor associated with main pancreatic duct dilation or believed to be the cause of AP (in the site-PI's judgment).
5. Prior pancreatic surgery, including, but not limited to distal pancreatectomy, pancreaticoduodenectomy, pancreatic necrosectomy, and Frey procedure.
6. Severe systemic illness that in the judgment of the investigative team will confound outcome assessments and immunological outcomes or pose additional risk for harm, including the history of solid organ transplant, acquired immunodeficiency syndrome (AIDS), active treatment for cancer (except non-melanoma skin cancer) within 12 months prior to enrollment, chronic kidney disease with eGFR <30 or on dialysis prior to AP, and cirrhosis (based on imaging or biopsy), or any other medical condition that in the opinion of the site-PI carries a life expectancy of <12 months.
7. Known pregnancy at the time of enrollment.
8. Incarceration.
9. Any other condition or factor that would compromise the participant's safety or the scientific integrity of the study.