Female hamsters, infected intracardially (i.c.) with 1.0–2.0 × 105 amastigotes of Leishmania donovani produced offspring, following mating, which, when immunized subcutaneously with 1.0 × 107 amastigotes at 8 weeks of age, were more resistant to i.c. challenge 6 weeks later than were hamsters born to non-infected mothers. Offspring of mothers infected with as many as 6.0 × 106 amastigotes demonstrated no greater capacity for immunization than did those of mothers infected with 1.0 × 105 amastigotes. Sensitization of offspring of infected mothers apparently is transplacental since the effect could only be seen in offspring of infected mothers and not in those of normal mothers weaned by infected dams. Offspring of female hamsters immunized by footpad inoculation of 1.0 × 107 amastigotes exhibited reduced spleen parasite burdens when challenged at 8.5 weeks of age and reduced spleen and liver parasite burdens when challenged at 16 weeks of age, compared to offspring of non-immunized hamsters; this effect was not noted following challenge of offspring of the two groups within 1 day of weaning. The passage of parasites from mother to young during gestation and/or nursing apparently does not occur since, at 125 days of age, no parasites were observed in spleen or liver impression smears of offspring of hamsters infected i.c. with 6.0 × 106 amastigotes while parasites were seen in such smears of hamsters infected, 120 days previously, with 10 amastigotes i.c. Thus, sensitization to immunization in offspring of infected hamsters and to challenge of offspring of immunized hamsters is apparently transplacental, effected either by soluble leishmanial antigen, soluble lymphocyte (or transfer) factor, or by cells.
Charles and Johanna Busch Pre-Doctoral Fellow of the Bureau of Biological Research.