Effects of neonatal anti-delta antibody treatment on the murine immune system. I. Suppression of development of surface IgD+ B cells and expansion of a surface IgM+ IgD- B lymphocyte population.

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Abstract
Lymphocytes that bear surface (s) IgD make up the majority of B cells in mature mice and are the precursors of most antibody secreting cells in primary immune responses made by these mice. In order to study the functional capabilities of the minority sIgD- B lymphocyte population and to gain insight into the possible roles of sIgD, we attempted to abort the development of sigD+ B cells and to expand the sigM+IgD- B cell population by treating mice from birth with affinity-purified rabbit antibodies specific for mouse IgD (RaM delta). RaM delta-suppressed mice had no detectable sIgD+ spleen, lymph node, or bone marrow cells and, on average, only 20% as many sIgM+Ia+ splenic B cells as control mice but had normal numbers of splenic T cells. Lymph nodes from anti-delta suppressed mice were even more depleted of B cells than were spleens from these mice, whereas the percentage of bone marrow B cells in these mice was relatively normal. Germinal centers of anti-delta suppressed mice were fairly normal in appearance, whereas follicular mantle layers, the locus of most sIgD+ B cells in normal mice, were greatly depleted. In addition to their lack of sIgD, splenic B cells of anti-delta suppressed mice differed from those found in control mice in that they bore, on average, twice as much sIgM as control cells, and in that they included an increased percentage of large, DNA synthesizing cells as compared with spleen cells from control mice. However, most sIgM+IgD- splenic B cells from anti-delta suppressed mice were small, nonproliferating cells. B cells from anti-delta suppressed mice insert little or no sIgD into their cell membranes since they continued to bear no detectable sIgD 2 days after in vivo neutralization of RaM delta and since, unlike B cells from control mice, they failed to be activated by a single in vitro injection of a goat anti-mouse delta antibody. Despite their lack of sIgD+ B cells, anti-delta suppressed mice had relatively normal levels of serum IgG as well as normal to increased levels of serum IgM. Thus, sIgM+IgD- B cells appear to have the potential of differentiating into Ig secreting cells in vivo without acquiring sIgD.