Surface immunoglobulin phenotype of complement receptor-positive and complement receptor-negative B cells of normal and xid immunodeficient mice*
Single-and dual-parameter fluorescence-activated cell sorter analyses of complement receptor-positive and -negative (CR' and CR-) splenic B cells of normal and xid immunodeficient mice were performed to determine the frequencies of surface (s) IgM+ and sIgD+ cells, as well as the quantities of sIgM and sIgD on these cells. Single parameter analysis revealed identical frequencies of sIgM+ and sIgD+ cells in the CR+ B cell population of normal mice. In contrast, the percentage of sIgM+ cells exceeded that of sIgD+ cells in the CR-normal and CR+ xid B cell population to a similar extent. CR-xid B cells showed an even greater discrepancy between sIgM+ and sIgD+ cells.
Dual-parameter analysis of CR+ normal B cells showed the typical sIg phenotype of mature B cells, i.e. an intermediate density of sIgM and a high density of sIgD. The CR' xid B cell population displayed an increase in cells with high sIgM and no-to-low sIgD and a decrease in cells with intermediate sIgM and high sIgD when compared to CR' normal cells. CR-B cells from normal and xid immunodeficient mice were similar in that both consisted largely of a cell population with low sIgM and no-to-low sIgD. However, the CRnormal B cell population also contained cells with intermediate sIgM and high sIgD, which were lacking in the CR-xid cell population.
Similar results were obtained when CR+ and CR-B cells from normal and xid mice were purified from a small resting B cell population, isolated by elutriation. This indicates that the sIg phenotype of CR-cells is not due to the presence of large cells which have lost sIgD during activation.