The present invention relates to antibodies, or antigen binding fragments, variants, or derivatives thereof. In particular embodiments, the present invention relates to recombinant monoclonal antibodies, specific for mouse CD20. In addition, the present invention relates to nucleic acid molecules encoding such antibodies, or antigen binding fragments, variants, or derivatives thereof, and vectors and host cells comprising such nucleic acid molecules. The invention further relates to methods for producing the monoclonal antibodies or antigen binding fragments, variants, or derivatives thereof of the invention, and to methods of using these antibodies or antigen binding fragments, variants, or derivatives thereof, alone or in combination, in animal models of disease.