Publications

Activation of T lymphocytes infected with the human immunodeficiency virus-1 (HIV-1) results in enhancement of viral replication mediated in part by activation of cellular NF kappa B capable of binding directly to sequences in the viral long terminal repeat, or LTR. Together with CD4+ T cells, macrophages constitute a major target for infection by HIV-1. Unlike lymphocytes, however, stimulation of mononuclear phagocytes is not associated with cell division and proliferation. Human monocyte-derived macrophages transfected with HIV-LTR-CAT constructs demonstrated down-regulation of CAT activity after stimulation with bacterial lipopolysaccharide (LPS) that mapped to a region distinct from NF kappa B binding sites. In contrast, fresh monocytes and the promonocytic U937 cell line both demonstrated up-regulation of HIV-LTR-CAT expression by LPS. Differentiation of U937 by PMA to establish a nondividing phenotype resulted in down-regulation of transfected HIV-LTR-CAT activity by LPS similar to that in mature macrophages. Human monocyte-derived macrophages infected with HIV-1 in vitro demonstrated a decrease in viral p24 release after incubation in LPS that was comparable to the negative regulation that occurred in the transient transfection assays. Factors controlling HIV replication may differ in dividing and nondividing hematopoietic cells and may contribute to restricted viral expression in nondividing cells.

Cultured glomerular mesangial cells (MC) respond to low concentrations of bacterial endotoxin (ET) by secreting prostaglandins and interleukin-1. To evaluate further the nature of ET-induced mesangial cell activation, the authors evaluated the effects of this agent on MC morphology and cytoskeletal organization. Bacterial ET, in concentrations as low as I ng/ml, induced reversible membrane ruffling, cellular rounding, and extension of many filopodia and lamellopodia. Augmented fluid-phase pinocytosis occurred in parallel, as determined by transmission electron microscopy and tritiated sucrose uptake. These cellular morphologic and functional changes were associated with an extensive, but reversible, depolymerization of actin microfilaments. Actin gene expression was also modified by ET. At 4 to 6 hours after ET exposure, Northern blot analysis showed a twofold to fourfold increase in actin mRNA levels. In situ hybridizations of ET-stimulated cells at the light and electron microscopic levels demonstrated a markedly asymmetric distribution of actin mRNA, which was localized in the cellular periphery at filopodial and lamellopodial extensions, presumably sites of new actin protein synthesis. It is concluded that ET effects on MC are distinct from the nonspecific lytic or 'toxic' actions described for other cell types. Endotoxin induces a global activation of this cell type associated with major changes in membrane structure, cytoskeletal organization, and gene expression, which resemble in many respects the responses to peptide mitogens.