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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.

In this study, we have examined the effects of autologous monocytes and T-lymphocytes on gamma-interferon (gamma-IFN)-induced inhibition of granulocyte-monocyte progenitor cells (CFU-GM) in vitro. Depletion of adherent cells from the mononuclear fraction of normal bone marrow (NBM) resulted in a significant reduction in the inhibitory effects of gamma-IFN on CFU-GM growth, whereas T-lymphocyte depletion had no effect. Adding back autologous monocytes to the underlayer fraction of agar culture resulted in a concentration-dependent enhancement of gamma-IFN-induced CFU-GM inhibition that did not require cell-cell contact. Adding back autologous T-lymphocytes had no effect and did not synergize with monocytes in enhancing gamma-IFN-induced inhibition. Based on the use of indomethacin and the pattern of CFU-GM subset growth, it was determined that prostaglandin E was unlikely to be the humoral inhibitory factor involved in this process. However, the effects of monocytes were completely reversed in the presence of a neutralizing monoclonal antibody to tumor necrosis factor (TNF), suggesting that monocyte-derived TNF was responsible for the enhancement of gamma-IFN-induced CFU-GM inhibition. This observation was further supported by the ability of gamma-IFN to induce an eightfold increase of baseline monocyte TNF secretion in agar culture. These data suggest that gamma-IFN may inhibit progenitor cell growth in vitro through indirect humoral mechanisms involving monocyte-derived TNF, as well as through direct inhibitory effects on CFU-GM proliferation. Because monocytes are a component of the bone marrow microenvironment, the ability of gamma-IFN to induce biologically relevant levels of monocyte-derived TNF may play an important role in the negative regulation of hematopoiesis.

Cells from most cases of acute myeloblastic leukemia (AML) proliferate in vitro in response to one or more colony-stimulating factor (CSF). Previous studies have suggested that some AML cells can produce their own CSFs, but the frequency of this phenomenon is unclear. In this study, Northern blot hybridization was used to detect mRNA transcripts for granulocyte-monocyte CSF (GM-CSF), granulocyte-CSF (G-CSF), and macrophage-CSF (M-CSF) in 22 randomly selected cases of AML. Ten cases expressed one CSF transcript (generally M-CSF), one case expressed two CSF transcripts, and six cases expressed all three. The expression of CSF transcripts did not significantly correlate with the French-American-British classification, with the possible exception that four of the five cases expressing all three CSF mRNAs were FAB M1. Six cases had autonomous growth of clonogenic cells in agar, and all six cases expressed one or more type of CSF transcript. None of the five evaluated cases lacking all three CSF transcripts had autonomous growth. However, there were many cases in which CSF transcripts were present and no autonomous growth was observed. In response to exogenously added human recombinant CSFs, 11 of 18 cases proliferated in response to GM-CSF, 8 of 18 cases in response to G-CSF, and 0 of 10 cases in response to M-CSF. Response to a CSF was not significantly correlated with the presence or absence of CSF transcripts, particularly for M-CSF. These results show that CSF transcripts are frequently detected in AML, although with a substantial degree of heterogeneity. It is possible that CSF production contributes to unregulated growth in some cases of AML.