FACS analysis of peripheral blood and bone marrow cells from hPLAP-tg rats and immune response of wild-type rats to transgenic cells. The single parameter fluorescence histograms show hPLAP expression (mAb clone 8B6) on the majority of peripheral blood leukocytes (A) and practically all bone marrow cells (B) in hPLAP-tg rats (grey area), but no expression in wild-type rats (white area). When peripheral blood leukocytes from hPLAP-tg rats are incubated with serum from a naïve wild-type rat, and stained for bound antibodies, no staining is seen (black curve, C). However, serum from the same wild-type intraperitoneally injected with cells from transgenic donors 3 times shows strong reactivity with peripheral blood leukocytes from hPLAP-tg rats (C, green, after 2 injections; red, after 3 injections), indicating the induction of circulating antibodies against transgenic cells in the recipient. Ten-thousand cells were analyzed in each sample. In a mixed lymphocyte reaction protocol (D), co-culture of hPLAP-tg spleen cells with spleen cells from wild-type rats previously injected with cells from hPLAP-tg rats, but not from naïve wild-type rats, caused increased cell proliferation. ConA was used as a positive control. 5 × 105 spleen cells per well were cultivated for 5 days (n = 8 wells each). * denotes P < 0.05 vs. indicated control group by one-way ANOVA followed by least significant difference test.