Inhibition of calcium and glucose uptake by murine leukemia L5178Y cells treated with antiserum

In vitro growth inhibition of murine leukemia cells by antibody specific for the major envelope glycoprotein (gp71) of Friend leukemia virus

An in vitro complement (C')-independent growth cytostasis model is described in which the replication of Friend leukemia virus (FLV)-induced erythroleukemia cells (of the FLC-745 cell line) is inhibited by goat serum directed against the major FLV envelope glycoprotein, gp71. The cytostatic effect is reversible, with the degree of this reversibility dependent on both the concentration and duration of exposure to immune serum. The inhibitory factor in heat-activated goat anti-FLV gp71 (delta G alpha FLV gp71) serum has been identified as virus-specific IgG antibody, and F(ab')2 fragments of this antibody are highly effective in suppressing FLC-745 cell growth. Studies with various murine leukemia and lymphoma cell lines, as well as with a panel of antisera directed against various murine oncornaviruses or viral proteins, have demonstrated that antibodies reactive with the group or type determinants of FLV gp71 are capable of mediating cytostasis. Under conditions of antibody-mediated growth inhibition of FLC-745 cells, specific modulation of gp71 expression is followed by nonspecific modulation of H-2d antigen expression. In addition, considerable cell death occurs in cytostatic cultures which is accompanied by continued division (as measured by DNA synthesis) of a portion of the cell population. Cytofluorimetric analysis of nuclei from growth-inhibited FLC-745 cells demonstrates a diminution in the frequency of cells in the G2/M phase of the cell cycle. It is suggested that antibody-mediate FLC-745 cell growth inhibition operates via a blockade of the cell cycle which prevents most cells in the population from traversing G2/M. While these blocked cells appear to be subject to slow cytolysis by a C'-independent mechanism, a portion of the cells escape this blockade and continue to replicate, thus offsetting the death of the former cells to yield a relatively constant density of viable cells for at least 72-96 h of growth inhibition. The possible relevance of this in vitro phenomenon to in vivo passive therapy against FLV-induced disease with G alpha FLV gp71 and similar antisera is briefly considered.

Antibody-induced cell-cycle synchrony

Synergism between specific antibodies and cytotoxic drugs in killing tumor cells is an established phenomenon. When cells grown in a suspension culture are treated with antibody, a subsequent increase in susceptibility to cytosine arabinoside has been shown to be due to the induction of cell-cycle synchrony. This observation may lead to a novel way of investigating cell-cycle-dependent processes and also an aspect of tumor-antibody interactions that is not generally recognized.

Effect of antiserum on leukemia L5178Y cells: [3H]thymidine incorporation does not reflect DNA synthesis

1. The total amount of DNA present in L5178Y cells treated with antiserum in the absence of complement was decreased whereas the rate of incorporation of [3H]thymidine into DNA during a 1 hr pulse was increased as compared with those of controls. 2. This increase in specific activity of [3H]thymidine in the DNA of antiserum-treated cells appeared to be due, at least in part, to an increase in thymidine kinase activity.