Relationship of human macrophage agglutination factor to other fibronectins.

Human macrophage agglutination factor (MAggF) is a lymphokine with a number of biochemical and immunochemical similarities to the fibronectins (FN). The present study was undertaken to define this relationship more exactly. Peripheral blood mononuclear cells (PBMC) and cloned human CD4+T-cell lines synthesized both MAggF and immunoreactive FN de novo following antigen or mitogen activation. MAggF produced under those conditions co-purified with an immunoreactive FN on gelatin-affinity and gel-filtration chromatography. This FN had a consistently slightly smaller relative molecular mass than plasma FN on both immunoblotting and gel filtration. Purified human MAggF was extremely active: it agglutinated human monocytes at fM concentrations and was up to 2,000,000 times more active in agglutinating mononuclear phagocytes than other purified FN. The action of MAggF on monocytes was dependent on at least two antigenically distinct cell-surface FN receptors. We suggest that the extreme activity of MAggF is a result of co-operative interactions between FN domains on the MAggF molecules and multiple distinct classes of FN receptors on responding cells

The Late Stage of Human Immunodeficiency Virus Type 1 Assembly Is an Energy-Dependent Process

Several recent studies have indicated the involvement of host cell factors in human immunodeficiency virus type 1 (HIV-1) assembly. To ascertain whether ATP-dependent factors play a role in this process, we quantified virus-like particle (VLP) production by ATP-depleted cells. Pharmacological ATP depletion abrogated VLP production without affecting cell viability or inducing degradation of HIV-1 Gag protein. This effect occurred even when the ATP-depleting agents were added 1 h into the assembly process, and it was reversed by removal of these agents. ATP depletion did not affect Gag membrane binding or multimerization. Density gradient analysis indicated that HIV-1 assembly intermediates were stalled late in the assembly process. This conclusion was further supported by electron microscopy analysis, which revealed a preponderance of plasma membrane-associated stalk-like structures in the ATP-depleted cells. Since no HIV-1 proteins bind or hydrolyze ATP, these findings indicate that an ATP-requiring cellular factor is an obligatory participant late in the HIV-1 assembly process