Regional cellular responses to intraperitoneal infection.

Leucocytes in different body compartments were examined in a murine intra-abdominal abscess model: (i) peripheral blood; (ii) peritoneal exudate; (iii) abscess wall; and (iv) abscess pus, with respect to their phagocytic ability, CR3 expression and Ia antigen expression (murine MHC antigen). The ability of serum or supernatant in each compartment to opsonize Staphylococcus aureus was also determined. Mice responded to caecal ligation and puncture (CLP) with systemic monocytosis, an increased amount of opsonins in peritoneal fluid and an increased phagocytosis in pus leucocytes. This increased phagocytic ability and CR3 expression both subsequently decreased. Monocyte/macrophage Ia expression was reduced in all measured compartments over time. In contrast, sham-operated animals, without an intra-abdominal abscess, responded to operation with an even greater increase in peritoneal exudate phagocytic ability and in monocyte/macrophage Ia expression in all compartments which was sustained beyond 1 week. Decreased peritoneal exudate cell and peripheral blood Ia was still present after 28 days in CLP animals, compared with both sham and normal animals (P less than 0.05, P less than 0.02, respectively). For all parameters, changes observed in peripheral blood did not reflect those present near the site of infection. Proper understanding of local or regional infection must take into account and ultimately alter these generally unappreciated changes in and about the actual site of infection.