Enables complement receptor activity. Acts upstream of or within with a negative effect on complement activation, alternative pathway. Acts upstream of or within several processes, including cellular response to lipopolysaccharide; immunoglobulin mediated immune response; and skeletal system development. Located in external side of plasma membrane. Human ortholog(s) of this gene implicated in common variable immunodeficiency; nasopharynx carcinoma; and systemic lupus erythematosus. Orthologous to human CR2 (complement C3d receptor 2). [provided by Alliance of Genome Resources, Apr 2022]