Vascular cell adhesion molecule-1 expressed by peritoneal mesothelium partly mediates the binding of activated human T lymphocytes.

Adhesion molecules such as selectins and integrins are known to mediate leukocyte attachment and transmigration through activated vascular endothelium. However, the molecules that mediate subsequent leukocyte entry into nonvascular spaces such as the abdominal cavity during states of peritoneal inflammation have not been identified. Because the peritoneal mesothelial lining represents the final barrier to leukocyte migration into the abdomen, it is likely that adhesion molecules expressed by mesothelial cells are involved in this process. We have developed an in vitro binding assay using confluent layers of normal human mesothelial cells to determine which adhesion molecules might be involved in T lymphocyte-mesothelial recognition. Normal peripheral blood T lymphocytes exhibit low-level specific binding to mesothelium (mean 13% specific binding, n = 4), which is enhanced by phorbol myristate acetate (PMA) treatment (mean 38% specific binding, n = 4). This binding is significantly inhibited in the combined presence of antibodies reactive with CD29 and CD18, suggesting a role for beta 1 and beta 2 integrins, respectively, in this interaction. Interestingly, cultured human mesothelial cells were shown to express vascular cell adhesion molecule-1 (VCAM-1), suggesting that this molecule might function as a counter-receptor for alpha 4 beta 1 expressed by T lymphocytes. Mesothelial cells were also noted to express ICAM-1, CD29, and CD44, but not CD18 or selectins. VCAM-1 expression was not a constitutive property of freshly obtained mesothelial cells but was inducible upon culture in the presence of either interleukin-1 (IL-1), tumor necrosis factor (TNF), or PMA. Neutralizing antibodies reactive with either alpha 4, VCAM-1, or CD29 were all equally capable of inhibiting the binding of activated leukocytes to mesothelial cells (in the presence of anti-CD18 antibody). Mesothelial VCAM-1 was found to have a molecular mass of 110 kD and an mRNA transcript of approximately 3.2 kb, consistent with the predominant VCAM-1 species found in activated endothelium. These data suggest that functional VCAM-1 is expressed on activated mesothelial cells and may play a role in the distal arm of leukocyte trafficking to the abdominal cavity.