The relationship between surface immunoglobulin isotype and immune function of murine b lymphocytes: II. Surface immunoglobulin isotopes on unprimed b cells in the spleen*

We investigated the ability of IgM-, IgD-, and IgG-bearing cells from the spleens of unprimed (BALB/c × C57BL/Ka)F₁ mice to restore the adoptive primary anti-BSA and anti-DNP antibody responses. Purified populations of isotype-specific cells were prepared by immunofluorescent staining and sorting on the fluorescence activated cell sorter. Bright or dull cells were transferred to irradiated syngeneic recipients which were challenged with DNPoBSA in complete Freund’s adjuvant. Unfractionated spleen cells as well as IgM- and IgDbearing cells restored the adoptive primary IgM and IgG antibody response. IgG-bearing cells restored a vigorous adoptive response which was all IgG (2- mercaptoethanol resistant). Depletion of IgG-bearing cells markedly increased the adoptive IgM response, and depletion of IgM-bearing cells markedly increased the IgG response. However, depletion of IgD-bearing cells resulted in a considerable reduction in the IgG response. The latter finding indicates that there is a subpopulation of IgD-bearing cells which express little or no surface IgM and which make a considerable contribution to the adoptive primary IgG response.