The importance of interleukin-1beta (IL-1beta) in the pathogenesis of acute pancreatitis has been demonstrated by dramatic attenuation of pancreatic destruction and significant increases in survival when its actions are inhibited. The pancreas has been shown to be a major producer of IL-1beta during pancreatitis but the cell(s) of origin remains unknown. Hypothesizing that infiltrating leukocytes contribute substantially, the intrapancreatic production of IL-1beta was examined after specific leukocyte populations were manipulated in vivo prior to the induction of pancreatitis. Sixty-four adult male Swiss mice were assigned to one of four groups 48 hr prior to induction of pancreatitis: (1) PMN depletion via anti-murine PMN antiserum. [PMN-d], (2) macrophage (Mphi) depletion via anti-macrophage antiserum [Mphi-d], (3) PMN and Mphi depletion [PMN+Mphi-d], and (4) Immunocompetent Pancreatitis. Edematous pancreatitis was induced in all experimental groups by caerulein (50 microg/kg/hr ip X 4). Animals were sacrificed 6 hr after induction of pancreatitis with severity determined by blind histologic grading and serum amylase, lipase, and interleukin-6 (IL-6) levels. Intrapancreatic IL-1beta production was determined by immunohistochemistry and semiquantitative differential RT-PCR. Pancreatitis developed in all animals receiving caerulein; however, leukocyte-depleted animals showed significantly attenuated levels of serum amylase, lipase, and IL-6, as well as lower histologic severity scores. Similarly, pancreatitis induction in immunocompetent mice showed pancreatic infiltration of IL-1beta-producing cells, whereas the leukocyte-depleted animals had significantly decreased numbers (PMN+Mphi-d < Mphi-d < PMN-d). IL-1beta mRNA was upregulated in all animals developing pancreatitis with significantly lower levels seen in the leukocyte-depleted groups. We conclude that infiltrating leukocytes, both neutrophils and macrophages, are responsible for the majority of intrapancreatic IL-1beta production during acute pancreatitis. The elimination of leukocytes and their products, including IL-1beta, significantly decreases the severity of pancreatic destruction.