Abstract

To examine the in vivo function of IgD we generated mice deficient for IgD by gene targeting. The IgD-mice show a reduced B-cell compartment with 30-50% less B cells in the spleen and lymph nodes but show a normal pre-B-cell compartment. The surface-IgD- B cells express two to three times more surface IgM than B cells of control animals. Serum concentrations of the immunoglobulin isotypes of IgD- mice are almost normal, indicating that surface-IgD expression is not necessary for class switching of B cells. Immunization experiments showed that IgD- mice could respond well to thymus-dependent and -independent antigens. After immunization normal germinal centers developed in the IgD- mice. These data suggest that IgD is not necessary for the induction of immune responses but may be important in homeostasis of cells in the B-cell compartment.