Conditions which induce sustained production of beta chemokines (CCL3/MIP-1alpha, CCL4/MIP-1beta, CCL5/RANTES) have been associated with a lower risk of HIV transmission; similarly, natural mutations that enhance production of SDF-1, and therefore increase competition for the CXCR4 coreceptor, were shown to play a protective role in HIV infection [72,83]. The gene discussed is CCL4; the disease is HIV infectious disease.