CCR5 and infection: In addition, CD4+ lymphocytes from the LTNP subpopulation who displayed anti-CCR5 antibodies were resistant to in vitro infection with R5-tropic HIV-1 strains, due to CCR5 downregulation; finally, anti-CCR5 antibodies blocked in vitro infectivity of HIV primary isolates belonging to clades A, B and C. The level of ECL1-specific anti-CCR5 antibodies appeared to be correlated with levels of HIV exposure, being lower in seronegative ESN subjects and higher in seropositive LTNP individuals (0.1% vs. 8% of the total antibodies, respectively).