IL-10 induces the development of immunosuppressive CD14(+)HLA-DR(low/-) monocytes in B-cell non-Hodgkin lymphoma.

The biological role of monocytes and macrophages in B-cell non-Hodgkin lymphoma (NHL) is not fully understood. We have previously reported that monocytes from patients with B-cell NHL have an immunosuppressive CD14(+)HLA-DR(low/-) phenotype that correlates with a poor prognosis. However, the underlying mechanism by which CD14(+)HLA-DR(low/-) monocytes develop in lymphoma is unknown. In the present study, we found that interleukin (IL)-10, which is increased in the serum of patients with B-cell NHL, induced the development of the CD4(+)HLA-DR(low/-) population. Using peripheral blood samples from patients with B-cell NHL, we found that absolute numbers of CD14(+) monocytic cells with an HLA-DR(low/-) phenotype were higher than healthy controls and correlated with a higher International Prognostic Index score. IL-10 serum levels were elevated in lymphoma patients compared with controls and were associated with increased peripheral monocyte counts. Treatment of monocytes with IL-10 in vitro significantly decreased HLA-DR expression and resulted in the expansion of CD14(+)HLA-DR(low/-) population. We found that lymphoma B cells produce IL-10 and supernatants from cultured lymphoma cells increased the CD14(+)HLA-DR(low/-) population. Furthermore, we found that IL-10-induced CD14(+)HLA-DR(low/-) monocytes inhibited the activation and proliferation of T cells. Taken together, these results suggest that elevated IL-10 serum levels contribute to increased numbers of immunosuppressive CD14(+)HLA-DR(low/-) monocytes in B-cell NHL.

Differential regulation of growth and checkpoint control mediated by a Cdc25 mitotic phosphatase from Pneumocystis carinii.

Pneumocystis carinii is an opportunistic fungal pathogen phylogenetically related to the fission yeast Schizosaccharomyces pombe. P. carinii causes severe pneumonia in immunocompromised patients with AIDS and malignancies. Although the life cycle of P. carinii remains poorly characterized, morphologic studies of infected lung tissue indicate that P. carinii alternates between numerous small trophic forms and fewer large cystic forms. To understand further the molecular mechanisms that regulate progression of the cell cycle of P. carinii, we have sought to identify and characterize genes in P. carinii that are important regulators of eukaryotic cell cycle progression. In this study, we have isolated a cDNA from P. carinii that exhibits significant homology, but unique functional characteristics, to the mitotic phosphatase Cdc25 found in S. pombe. P. carinii Cdc25 was shown to rescue growth of the temperature-sensitive S. pombe cdc25-22 strain and thus provides an additional tool to investigate the unique P. carinii life cycle. Although P. carinii Cdc25 could also restore the DNA damage checkpoint in cdc25-22 cells, it was unable to restore fully the DNA replication checkpoint. The dissociation of checkpoint control at the level of Cdc25 indicates that Cdc25 may be under distinct regulatory control in mediating checkpoint signaling.

Pneumocystis carinii contains a functional cell-division-cycle Cdc2 homologue.

Pneumocystis carinii causes life-threatening pneumonia in immunocompromised patients. The inability to culture P. carinii has hampered basic investigations of the organism's life cycle, limiting the development of new therapies directed against it. Recent investigations indicate that P. carinii is a fungus phylogenetically related to other ascomycetes such as Schizosaccharomyces pombe. The cell cycles of S. pombe and homologous fungi are carefully regulated by cell-division-cycle molecules (cdc), particularly cell-division-cycle 2 (Cdc2), a serine-threonine kinase with essential activity at the G1 restriction point and for entry into mitosis. Antibodies to the proline-serine-threonine-alanine-isoleucine-arginine (PSTAIR) amino-acid sequence conserved in Cdc2 proteins specifically precipitated, from P. carinii extracts, a molecule with kinase activity consistent with a Cdc2-like protein. Cdc2 molecules exhibit differential activity throughout the life cycle of the organisms in which they occur. In accord with this, the P. carinii Cdc2 showed greater specific activity in P. carinii trophic forms (trophozoites) than in spore-case forms (cysts). In addition, complete genomic and complementary DNA (cDNA) sequences of P. carinii Cdc2 were cloned and found to be most closely homologus to the corresponding sequences of other pathogenic fungi. The function of P. carinii cdc2 cDNA was further documented through its ability to complement the DNA of mutant strains of S. pombe with temperature-sensitive deficiencies in Cdc2 activity. The P. carinii cdc2 cDNA restored normal Cdc2 function in these mutant strains of S. pombe, and promoted fungal proliferation. These studies represent the first molecular analysis of the cell-cycle-regulatory machinery in P. carinii. Further understanding of P. carinii's life cycle promises novel insights for preventing and treating the intractable infection it causes in immunocompromised patients.