| Description |
Studies were undertaken to investigate the role of peripheral blood leukocytes and spleen cells in age-related host resistance to viral infection. Initially, peripheral blood leukocyte and spleen cell cultures derived from adult ewes and 70 to 145 day gestational age fetal lambs were examined for their ability to produce interferon and support viral replication (the complete ovine gestational period is normally 150 days). Bleutongue (BTV), Chikungunya (CV), Semliki Forest (SFV), Newcastle disease (NDV), vesicular stomatitis (VSV), and vaccinia viruses, and herpesvirus hominis type II (HVH-II), failed to replicate to detectable levels in either fetal or adult cell cultures. No difference in either the levels or the kinetics of interferon production between virus-infected adult and fetal cell cultures was observed. Mean levels of peak interferon production induced by BTV, CV, SFV, NDV, and HVH-II or approximately 1000-3000 units/ml were demonstrated by 24 hrs post-virus inoculation. In contrast, mean interferon titers induced by VSV and vaccinia virus were significantly lower ( < 40-550 units/ml) and did not reach peak levels until 48 hrs post-inoculation. Variations in interferon levels induced on separate occasion using cells from the same adult donor and from the same donor age group were also observed. The interferon induced in both the fetal and adult cell cultures fulfilled the usual criteria for characterization. Blood leukocytes and spleen cells from adult sheep and 70 to 145 day gestation fetal lambs were found equally capable of inhibiting HCH-II and BTV infection in fetal lamb kidney (FLK) cell monolayers. Decreased cytopathic effect as well as diminished viral replication was demonstrated in the mixed cell cultures as compared with control FLK cultures. Increasing the total number of leukocytes or spleen cells from 0.5 x 10[6] to 2.0 x 10[6] resulted in enhanced antiviral protection and was accompanied by a concurrent increase in interferon production in mixed leukocyte-FLK cell cultures but not in mixed cultures of spleen and FLK cells. Ovine leukocytes did not inhibit the progression of HVH-II infection in mouse embryo fibroblast cultures, indicating that the antiviral effect was species specific. AN interferon-like substance was also detectable in mixed cultures containing leukocytes or spleen cells and uninfected FLK cell monolayers. Similar levels of the interferon-like substance were found when cultures of ovine leukocytes were added to either mycoplasma-contaminated FLK cell or antibiotic-treated FLK cells free of detectable mycoplasma. Uninfected ovine leukocyte, spleen cell, or FLK cell cultures did not produce interferon. A mycoplasmal species, Acholeplasma laidlawii, was subsequently isolated as a contaminant from the FLK cell line, and was shown to be associated with the induction of interferon in culture of ovine peripheral blood leukocytes. Broth cultures of the mycoplasma induced between 20 and 230 units/ml of interferon in leukocytes from two adult ewes. The amount of interferon produced correlated with the inoculum size of mycoplasma. Interferon production was associated with replication of the mycoplasma in the leukocyte cultures. Interferon was not induced by sterile mycoplasmal broth, a cell-free filtrate of the mycoplasmal cultures, or heat-inactivatied mycoplasma. The antiviral substance was characterized as interferon by the usual criteria. |
