Compositions are provided that comprise antibody against coreceptors for human immunodeficiency virus such as CCR5 and CXCR4. In particular, monoclonal human antibodies against human CCR5 are provided that bind to CCR5 with high affinity and are capable of inhibiting HIV infection at low concentrations. The antibodies can be used as prophylactics or therapeutics to prevent and treat HIV infection, for screening drugs, and for diagnosing diseases or conditions associated with interactions with HIV coreceptors.