[2 physiological factors selectively inducing 2 different stages of differentiation in the human lymphoblastoid cell line RPMI-6410t].

A factor was discovered in the human serum, placental serum from the umbilical cord of pregnant women and sera of peripheral blood from some healthy donors, which induces one of the late stages of differentiation: switching of IgM to IgG synthesis in the RPMI-6410t line of human lymphoblastoid B-cells. Earlier we observed the induction of another stage of differentiation in the same cell line: switching of IgM to IgA synthesis under the influence of a factor from the serum of cattle foetuses. We have shown that both the stages of differentiation are induced by the above factors not only in the initial cell line but also in a number of IgM+-sublines obtained by cloning with limiting dilutions. It was, thus, established that there are factors of class-specific switching and the B-cells of a human lymphoblastoid line are capable to proceed in vitro through different stages of differentiation inherent in the B-lymphocytes in vivo.