Strain specific 4-1BB and CD27 expression analysis in homozygous B-h4-1BB/hCD27 mice by flow cytometry. Splenocytes were collected from wild-type mice (+/+) and homozygous B-h4-1BB/hCD27 mice (H/H) stimulated with anti-CD3ε in vivo (7.5 μg/mice for 24 hours, i.p.), and analyzed by flow cytometry with anti-4-1BB antibody and anti-CD27 antibody. Human 4-1BB and CD27 were exclusively detectable in homozygous B-h4-1BB/hCD27 mice (H/H) but not in wild-type mice. Mouse 4-1BB were detectable in wild-type mice. Mouse CD27 can detectable both in wild-type mice and B-h4-1BB/hCD27 mice (H/H) for anti-mCD27 antibody can binding with human and mouse CD27.