A CD20-binding
polypeptide composition of the invention comprises at least one polypeptide selected from the group consisting of a polypeptide having the
amino acid residue sequence of SEQ ID NO: 1 (Vh of 2B8
antibody), but which includes at least one
amino acid residue substitution in SEQ ID NO: 1 selected from the group consisting of V12K, A14P, M20V, I48T, A68T, Q82E, T87R, S91T, and T106W; a polypeptide having the
amino acid residue sequence of SEQ ID NO: 4 (Vk of 2B8
antibody), but which includes at least one
amino acid residue substitution in SEQ ID NO: 4 selected from the group consisting of L11I, S12T, S27T, V29A, G40T, V59S, S69T, L72M, R76S, and V77L; a polypeptide having the
amino acid residue sequence of SEQ ID NO: 9 (Vh of Leu16
antibody), but which includes at least one
amino acid residue substitution in SEQ ID NO: 9 selected from the group consisting of V12K, M20V, A68T, Q82E, T87R, S91T, D93V, and A114T; and a polypeptide having the amino acid residue sequence of SEQ ID NO: 11 (Vk of Leu16 antibody), but which includes at least one amino acid residue substitution in SEQ ID NO: 11 selected from the group consisting of L11I, S12T, A59S, S69T, L72M, R76S, and V77L. The compositions are useful for diagnosis and treatment of autoimmune diseases.