Maturation of immunological reactivity in the fetal lamb infected with Akabane virus.

The development of cell-mediated immunological reactivity was studied in fetal lambs infected with Akabane virus. Examination of hepatic cells from fetuses between 40 and 75 days' gestation that had been infected via the transplacental route revealed inconsistent responses to Akabane, together with a uniform failure to respond to non-specific mitogens which contrasted with the behaviour of control, uninfected lambs. Following direct inoculation of fetal lambs with virus between 50 and 120 days' gestation, specific proliferative responses were observed on the part of the spleen cells from some. Direct challenge of fetal lambs of 4 months' gestation evoked cellular responses in lymph draining from the site of virus inoculation similar to those produced by challenge of adult sheep. The proliferative response of lymph-borne cells was substantially better if live, rather than inactivated, virus had been used.