Antibody production was evaluated in 62 recipients of blastomere-aggre
gation sheep-goat embryos, including 23 multiparous ewes, 21 multiparo
us does, 16 primiparous does, and 2 virgin does. The reactivity of ser
a collected weekly after the embryo transfer surgery was compared to t
hat of sera collected prior to the embryo transfer by means of 1) comp
lement-dependent cytotoxicity tests against peripheral blood lymphocyt
es (PBLs) from the parents of the embryo(s) 2nd from random-bred sheep
and goats, 2) hemagglutination and hemolytic assays with red blood ce
lls (RBCs) from the two sires of the embryo(s), and 3) assays with PBL
s and RBCs following absorptions with RBCs and PBLs from the parents a
nd offspring. Although cross-reactivity to ovine and caprine PBL antig
ens was present in the control sera of some recipients, xenogeneic imm
unization during pregnancy was detected in 20 of 30 recipients that ex
perienced term pregnancy. The xenogeneic response involved the product
ion of antibody that reacted with both PBLs and RBCs. Allogeneic respo
nses to RBCs were not observed, but allogeneic responses to PBLs occur
red frequently, beginning after the onset of the xenogeneic response i
n most recipients (98 +/- 28 vs. 57 +/- 15 days in ewes; 93 +/- 23 vs.
46 +/- 7 days in does; mean day of onset +/- SD). The onsets of the r
esponses were examined in conjunction with data collected on fetal and
placental chimerism to evaluate possible routes of immunization. The
onsets of the allogeneic responses and the limited serum reactivity to
third-party PBLs suggested that fetal lymphocytes leaking across the
placenta immunized the recipients to parentally inherited polymorphic
antigens. The xenogeneic responses were associated with placental chim
erism and appeared to involve the recognition of a species-specific mo
nomorphic antigen shared by PBLs and RBCs. Neither of the responses ap
peared to affect continuation of pregnancy to term.