Taken together, these data suggest that CD1d expression and iNKT cells are dispensable for B10-like CD5+ B cell accumulation and IL10-competence in mice prone to MBL-like and CLL-like disorders, but iNKT cells play a previously unrecognized role in regulating B cell progression through the transitional stages of B cell development. This evidence concerns the gene IL10 and B-cell chronic lymphocytic leukemia.