The present invention relates, e.g., to an isolated peptide comprising a sequence of contiguous amino acids that is at least about 60% identical (e.g., at least about 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 98% or 100% identical) to the sequence E-W-Q-K-E-G-L-V-T-L-W-L (SEQ ID NO:1), or an active variant of an isolated peptide comprising SEQ ID NO:1. Neutralizing antibodies generated by, or specific for, such peptides are also described, in particular antibodies which are specific for the HIV co-receptor, CCR5, and which inhibit infection of a host cell by HIV. Neutralizing single strand and complete human monoclonal antibodies against CCR5 are described. Methods of using such peptides or antibodies, for inhibiting infection by HIV, are also described.