B lymphocyte development in fetal liver

Abstract

AbstractSingle cell cultures of fetal liver cells (FLC) from day 13 of gestation onwards until birth develop lipopolysaccharide (LPS)‐reactive B cells which can be stimulated by LPS to IgM‐secreting plaque‐forming cells (PFC). When the cell concentration of FLC is lowered from 4 × 106 cells/ml to 4 × 10s cells/ml and below, the “in vitro” development to IgM‐secreting PFC is lost. Less and less FLC initiate growth to IgM‐secreting PFC as the cell concentration is lowered. Addition of 3 × 106 thymus cells/ml from either syngeneic mice or from xenogeneic Lewis rats dramatically increases the efficiency with which FLC develop into LPS‐reactive cells and initiate, after stimulation by LPS, clonal growth and maturation to IgM‐secreting PFC. Thus, day 13 FLC can be diluted to 1 × 106 cells/culture, day 16 FLC to 1 × 104 cells/culture and day 19 FLC to 3 × 101 cells/culture before the responding cells become limiting. The frequencies of precursor B cells developing to LPS reactivity and then to IgM‐secreting PFC in culture have been determined by limiting dilution analyses of FLC from day 13 to 19 (birth) of gestation and of liver cells at days 2, 4 and 7 after birth in cultures containing thymus cells and LPS. They are 1 precursor B cell in ∼ 1 × 106 FLC at day 13 of gestation, 1 in ∼ 1 × 10s at day 14, 1 in ∼ 3 × 104 at day 15, 1 in ∼ 1 × 104 at day 16, 1 in ∼ 2 × 103 at day 17, 1 in ∼ 1 × 102 at day 18 and 1 in ∼ 3 × 101 at day 19 of gestation. After birth, these frequencies decline rapidly to 1 in ∼ 3 × 102 at day 2, 1 in 3 × 103 at day 4 and 1 in less than 10s liver cells at day 7 after birth.