Omental dendritic cells: Ia expression and relation to macrophages

Three types of macrophagic cells in the mesentery of mice with special reference to LYVE-1-immunoreactive cells

Immunohistochemistry using whole mount preparations of the murine mesentery revealed two types of LYVE-1-immunoreactive cells with dendritic morphology other than F4/80(+) typical macrophages.The two types of LYVE-1(+) cells were regularly distributed with constant intervals throughout the mesentery and appeared to possess their own territory. Both types of LYVE-1(+) cells were weakly or moderately immunopositive for F4/80 antibody, a marker of macrophages,while F4/80(+) round macrophages were absolutely free from the LYVE-1 immunoreactivity. Only macrophages could ingest latex particles of 20 nm in diameter 3 h after a peritoneal injection.Peritoneal administration of lipopolysaccharide (LPS) induced a rapid reduction of LYVE-1 immunoreactivity in the cells with dendritic morphology followed by an increased immunoreactivity to F4/80 antibody, and simultaneously by dynamic changes in their shape. Under normal conditions,F4/80(+) macrophages in various connective tissues expressed LYVE-1, in contrast to lack of LYVE-1 in F4/80(+) macrophages within the parenchyma of visceral organs and macrophages residing in hepatic sinusoids and pulmonary alveoli. LYVE-1 may play a role in cell adhesion and migration of macrophagic cells within connective tissues rich in hyaluronan, and loss of LYVE-1 becomes a reliable sign of activated conditions in inflammation.

The pathobiology of peritonitis

The peritoneum is more than a mechanical covering that allows for the easy gliding of opposed peritoneal surfaces. The peritoneal mesothelial cells facilitate the action of powerful innate immune mechanisms. In addition, the peritoneal-associated lymphoid tissues contain unique cells that may play a crucial role in the localization of intraperitoneal infection. A clearer understanding of the molecular and cellular events underlying peritoneal functions in both the unstimulated and stimulated state will aid future treatment of peritonitis.

Development of the cellular response in the mouse omentum after intraperitoneal immunization

Using computer image analysis we studied the development of dense cellular and dense lymphoid areas ("milky spots") and of pendant lymphatic nodules in mouse omenta after intraperitoneal immunization with sheep red blood cells. In both euthymic (BALB/c and hairless BFU) and athymic hairless nu/nu BALB/c mice the proportion of newly developing activated omental areas (AOA) was biphasic, with distinct peaks on days 3-4 and 8-12 after immunization, and a trough on days 5 and 14. There was a small difference between athymic and euthymic BALB/c mice. In comparison with the nu/nu BALB/c mouse, the BFU mutant had a lower proportion of AOA on days 4 and 10. The athymic state is not thought to have a great influence on the AOA development; this depends on a basic macrophage defence, which is well developed in the athymic model, and is self-regulated and shaped by a sequence of cell immigration, settling, differentiation and emigration.