An anti-Fc³RIIB IgG-type antibody according to the invention or a fragment or derivative thereof contains at least one of (i) a variable region of the heavy chain comprising an amino acid sequence having at least 80% identity to amino acid sequence SEQ ID NO. 1 and (ii) a variable region of the light chain comprising an amino acid sequence having at least 65% identity to amino acid sequence SEQ ID NO. 2. A further anti-Fc³RIIB IgG-type antibody of the invention or a fragment or derivative thereof contains at least one of (i) a variable region of the heavy chain comprising an amino acid sequence having at least 90% identity to amino acid sequence SEQ ID NO. 3 and (ii) a variable region of the light chain comprising an amino acid sequence having at least 90% identity to amino acid sequence SEQ ID NO. 4. Pharmaceutical compositions of the invention contain such antibodies, fragments or derivatives thereof and can be used for the treatment or prophylaxis of autoimmune diseases.
