In vitro sensitization using thymocyte conditioned medium prepared from fetal calf, horse and rabbit sera.

Thymocyte conditioned medium (TCM) was prepared using 2 lots of fetal calf, and 1 lot each of horse and rabbit sera. The 4 TCM and the respective sera alone were compared in their ability to support primary in vitro sensitization to sheep red blood cells (SRBC) as assayed by direct plaque formation. As would be expected, only the fetal calf sera (FCS) supported the primary in vitro sensitization to SRBC, while the use of the TCM prepared from the FCS resulted in a doubling of direct plaque formation. TCM prepared from either the rabbit or horse sera did not provide adequate support for this primary antibody response to SRBC. These data indicate that only sera able to support primary in vitro sensitization is useful for the preparation of active TCM ultimately used in B cell sensitization for hybridoma formation.