Characterization of a virus variant produced by L cells persistently infected with lymphocytic choriomeningitis virus

Abstract

Continuous cultivation of murine L cells infected with lymphocytic choriomeningitis virus strain Armstrong leads to production of L(Arm) cells, which produce a predominantly cell-associated attenuated variant, the L(Arm) virus. The relatively few infectious particles that are released have lost the ability to form plaques on L cells and to cause illness in mice even if inoculated intracerebrally. Based on equal protein MrS, antigenicity and protein kinase activity, essentially identical results were obtained for the purified Armstrong and L(Arm) viruses. There was also no difference in production and release of particles with the potential to cause homologous interference. Such particles consisted of two types, one of which was highly susceptible to u.v.-irradiation, the other was highly resistant. In the case of the L(Arm) virus interfering particles, it appears that the u.v.-irradiation-susceptible forms represented infectious virus. Purified L(Arm) virus particles contained considerable quantities of subgenomic forms of (small) S-and (large) L-RNA and their complementary counterparts, which all appeared to be replicated autonomously in an unenriched manner.

Arenavirus Variations Due to Host-Specific Adaptation

“…Several studies describe the effect of the mutant spectra in the virus population phenotype making it more virulent or more attenuated according to the predominant quasi-species. For example, defective interfering particles could play a role in attenuating the virulence of a viral swarm by interfering with virus replication [91,92,93,94,95]. Therefore it is important to take into account that serial passages of arenaviruses in cell lines or animals could lead to the accumulation of mutations changing the viral phenotype from the natural reservoirs or from clinical samples [14,84,96].…”

Protection of Mice by an Attenuated Variant against the Wild-Type Lymphocytic Choriomeningitis Virus

“…This strategy was possible because of the known high sen sitivity of the infectious particles of L(Arm) virus and the extraordinary resistance of interfering particles against UV irradiation [5], L(Arm) virus was inactivated by UV irradiation of different exposure times and subsequently inoculated intracerebrally into mice; control L(Arm) virus was not exposed to UV irradiation. After the challenge with wt virus, the ID50 for the animals was calculated ( fig.…”

“…The homogenates were cleared of debris by centrifugation, and aliquots were filled into ampoules, which were snap frozen, stored at -70° and titrated in L cell Petri cultures. PFU and 50% mouse-lethal (LD50) and mouse-infectious doses (ID50) were titrated as described [5,6). In all experiments, always performed twice, all data points or columns represent the means and vertical bars denote the SE for 5 mice.…”

“…At intervals after intracerebral infection with 0.03 ml of 10 pg of wt virus (corresponding to 104 plaque-forming units, PFU) or with 0.03 ml of 10 pg of L(Arm) virus [5], or both, mice were killed by cervical dislocation. Brains were weighed and homogenized with known volumes of HBSS using a mortar, pestle and sand.…”

“…On the other hand, the appearance of such attenuated variants is combined with an undisturbed ability of replication in the organism, leading to an enhanced and accelerated immune reaction after infection with the pathogenic wild-type (wt) virus [1,2], A peculiar type, which is synthesized after the persistent infection of L cells with strain Armstrong lymphocytic choriomeningitis (LCM) virus, is named L(Arm) virus [3][4][5], In such cultures most, if not all, cells were infected and remained so during numerous divisions. The virus they produced had lost its potential to kill mice after intracerebral inoculation, while mice infected with the wt virus died on day 6 or 7 after the intracerebral inocula tion.…”