Isolation of inner cell masses from mouse blastocysts by immunosurgery or exposure to the calcium ionophore A23187.

Two techniques have been evaluated for their use in routinely isolating inner cell masses from mouse blastocysts by destroying the trophectoderm. The most efficient method of immunosurgery was a 15-min incubation in a 1:50 dilution of rabbit anti-mouse spleen antiserum followed by a 30--60-min incubation in guinea pig complement (1:10). Alternatively, inner cell masses were isolated by incubating blastocysts in 10(-5) M calcium ionophore A23187 in medium devoid of calcium and magnesium ions. Inner cell masses re-exposed to immunosurgery or the ionophore were less susceptible to lysis than the trophectoderm had been. The presence of the zona pellucida reduced trophectoderm lysis by immunosurgery in antiserum dilutions greater than 1:100, but had no effect when in the presence of ionophore. Inner cell masses were consistently isolated from expanded blastocysts which had been collected 78 h after ovulation and cultured in vitro for 24 h before exposure to ionophore or immunosurgery, whereas blastocysts which had developed for the full 102 h in vivo were frequently unaffected.