Interactions of murine leukemia virus (MuLV) with isolated lymphocytes. Iv. The role of mitogen‐induced cellular dna synthesis in virus infection and replication

Abstract

AbstractThe requirement for lymphocyte activation with mitogen during in vitro infection with murlne leukemia virus (MuLV) of Friend virus complex (FV) and the suppressive effects of MuLV on mitogen‐induced lymphocyte activation were studied in short‐term suspension cultures. Lymphocytes were infected with FV in vitro and then resuspended in culture medium with or without mitogens. Cells releasing infectious MuLV were enumerated as infectious centers (IC) on sarcoma virus+, leukemia virus‐fibroblasts. The accumulation of IC in cultures followed a Diphasic curve characterized by a plateau between days 1 and 4 and by a 10‐fold increase in IC between days 5 and 7. Stimulation with a B‐cell mitogen, bacterial lipopolysaccharide (LPS), following infection increased the number of IC 10‐to 40‐fold. On the other hand, stimulation with concanavalin A (Con A), a T‐cell mitogen, did not appreciably increase the number of 1C detected on day 5 post infection. Further studies on the role of LPS‐induced DNA synthesis in the enhancement of MuLV replication revealed two points: (1) a comparable enhancement of 1C was observed In cultures stimulated with LPS 2 days prior to or immediately after FV infection and in those which were not stimulated until 2 days after infection; (2) treatment of FV‐infected, LPS‐stimulated lymphocytes with 5,6‐bromodeoxyuridine (BrdUrd) and visible light at 2 days abolished cellular DNA and RNA synthesis but did not diminish subsequent MuLV replication; however, cellular DNA and RNA synthesis as well as MuLV replication were inhibited in LPS‐stimulated cells treated with BrdUrd and light prior to infection with FV. The uptake of both [3H]thymidine and [14C]uridine by LPS‐stimulated lymphocytes was inhibited by about 50% in the presence of infectious FV whereas uptake in Con‐A‐stimulated lymphocytes was not inhibited. Kinetic studies showed that the inhibition of LPS stimulation was not detectable until 24 h and later; the uptake of [3H] thymidine during the first 12 h after infection and mitogen activation was the same in infected and non‐infected cultures. Collectively, the results indicate that MuLV‐Friend infects normal B cells but that the subsequent virus replication and secondary infection remain low unless the cells are activated with a mitogen. Virus replication, however, eventually become independent of cellular DNA synthesis and the virus itself inhibits the cellular nucleic acid synthesis at a later stage in the infection.