The New World arenavirus Tacaribe virus induces caspase-dependent apoptosis in infected cells.

The Arenaviridae is a diverse and growing family of viruses that already includes more than 25 distinct species. While some of these viruses have a significant impact on public health, others appear to be non-pathogenic. At present little is known about the host cell responses to infection with different arenaviruses, particularly those found in the New World; however, apoptosis is known to play an important role in controlling infection of many viruses. Here we show that infection with Tacaribe virus (TCRV), which is widely considered the prototype for non-pathogenic arenaviruses, leads to stronger induction of apoptosis than does infection with its human-pathogenic relative Junín virus. TCRV-induced apoptosis occurred in several cell types during late stages of infection and was shown to be caspase-dependent, involving the activation of caspases 3, 7, 8 and 9. Further, UV-inactivated TCRV did not induce apoptosis, indicating that the activation of this process is dependent on active viral replication/transcription. Interestingly, when apoptosis was inhibited, growth of TCRV was not enhanced, indicating that apoptosis does not have a direct negative effect on TCRV infection in vitro. Taken together, our data identify and characterize an important virus-host cell interaction of the prototypic, non-pathogenic arenavirus TCRV, which provides important insight into the growing field of arenavirus research aimed at better understanding the diversity in responses to different arenavirus infections and their functional consequences.

[The immunity indices of BALB/c mice immunized with an inactivated antigen of the Machupo virus]. / Pokazateli immuniteta u myshei linii BALB/c, immunizirovannykh inaktivirovannym antigenom virusa Machupo.

The paper presents the data characterizing parameters of specific and nonspecific immunity in BALB/c mice immunized with gamma-ray-inactivated Machupo virus antigen or its formalinized antigen. The gamma-ray inactivated preparation was shown to be more immunogenic for BALB/c mice. A certain relationship between the time course of activity of nonspecific immunity factors in the immunized animals and the protective activity of the preparation under study was also noted. The decisive role of the T-cell part of the immune system was demonstrated in the resistance of this model animal to Machupo virus infection.

Interactions of Junin and Tacaribe viruses during mixed infections.

The interaction between Junin virus (JV) and Tacaribe virus (TACV) during mixed infections of RK13 cells was examined. The effects of a prior infection with JV upon TACV replication depended on the time between the two inoculations. Simultaneous infection of RK13 cells with TACV and JV did not alter the plaquing efficiency of TACV; but if there was a 1- to 24-hour delay between JV preinfection and TACV superinfection, a variable increase of TACV replication was observed. The enhancement of TACV replication by preinfection with JV was dependent on several factors, such as the MOI of both viruses and the integrity of the JV genome. This effect was also highly specific, as the plaquing efficiencies of the arenavirus Pichinde and the unrelated vesicular stomatitis virus were not affected by preinfection with JV at any multiplicity assayed. The majority of the progeny formed in cells superinfected with TACV 1 or 24 h after JV infection was partially neutralized by antisera to both viruses. This suggested that phenotypic mixing, with JV or TACV genomes enclosed within an envelope containing TACV and JV glycoprotein, had occurred.

Response of cells persistently infected with arenaviruses to superinfection with homotypic and heterotypic viruses.

Vero cell cultures persistently infected with the arenaviruses Junin, Pichinde, Tacaribe, and Tamiami were established and designated Vero-Jun, Vero-Pic, Vero-Tac, and Vero-Tam, respectively. Two types of carrier cultures could be easily distinguished: Vero-Jun and Vero-Tac systems were characterized by a lack of infectious virus production after a few cell transfers, whereas a more productive state with continuous release of virus was observed in Vero-Pic and Vero-Tam cultures. These differences appeared to be related to resistance of the culture to viral superinfection. In fact, Vero-Jun and Vero-Tac cultures totally excluded only the replication of the serologically more closely related arenaviruses Amapari, Junin, or Tacaribe, while the refractoriness of Vero-Pic and Vero-Tam cultures was extended to most of the virus group members. The resistance of Vero-Jun cells to superinfection by Junin or Tacaribe virus could be ascribed to the production of specific uv-resistant Junin interfering particles, which showed a specific range of interference against Junin and Tacaribe viruses. Interfering particles against homotypic and heterotypic arenaviruses were isolated from Vero-Pic cultures. However, the degree of interference developed by these Pic-interfering particles was not enough to fully explain reinfecting virus exclusion from Vero-Pic cultures. Viral susceptibility of persistent cultures is proposed as a useful tool to examine relationships of members of the arenavirus group.

In vitro induction of human polymorphonuclear leuckocyte damage by junin virus

Diferentes modelos experimentales, utilizando cepas patógenas de virus Junín (VJ), han reproducido la característica leucopenia con que cursa la enfermedad humana. Los mecanismos responsables de esta leucopenia son poco conocidos. Con el fin de indagar si el VJ posee algún efecto citopatógeno directo sobre leucocitos polimorfonucleares (PMN), se incubó una suspensión de PMN humanos con VJ, cepa XJCl3. Las células se obtuvieron de doadores sanos de banco de sangre y fueron separados en gradientes de Ficoll Hypaque, lográndose 98% de pureza. Se obtuvieron muestras secuenciales del sobrenadante y de las células para determinación de actividad enzimática (peroxidasa, betaglucuronidasa y lisozina), titulación de VJ y estudios morfológicos con microscopía de luz y electrónica. Se observó una pérdida gradual y constante de las granulaciones citoplásmicas entre las 2 y 10 horas post-infección (pi) disminución del número de células viables según prueba de exclusión de azul tripan, entre las 10 y 20 horas pi y un aumento de la concentración de enzimas lisosomales en el sobrenadante a partir de las 10h pi. Aparentemente no hubo replicación viral ya que luego de las 11h pi no pudo rescatarse infectividad por medio de técnicas convencionales. Para la producción de estos efectos, el virus necesita poseer su capacidad infectante intacta ya que el tratamiento previo con irradiación ultravioleta o con suero inmune anti-VJ previene cambios. Estas observaciones indican que el virus Junín infectante induce alteraciones tempranas irreversibles sobre los PMN