The invention relates to antibodies directed to α2β1 integrin and their uses, including humanized anti-alpha 2 (α2) integrin antibodies and methods of treatment with anti-α2 integrin antibodies. More specifically the present invention relates to humanized anti-α2 integrin antibodies comprising a heavy chain variable region, a light chain variable region, a human light chain constant region and a variant human IgG1 heavy chain constant region which exhibit altered effector function.