Thirty-three HIV-1 seropositive drug naive patients (18 males and 15 females) within the age range of 20-57 years (median = 33 years) were recruited in this study from the Regional STD Teaching Training & Research centre, Safdarjang Hospital, New Delhi, India during the period 2008-2011. The patients had a median CD4 count of 449 (range = 203-966) cells/cubic millimeter (Additional file 1: Table S1 ). The whole blood samples of HIV-1 positive donors were collected in EDTA vacutainers, plasma was separated by centrifugation at 300 g and stored in aliquots at -80°C until use. The plasma samples were heat inactivated at 56°C for 1 h before using in the assays. The patients have been previously shown to have high titers of anti-V3 Abs in their plasma and a good proportion of these V3 directed Abs displayed cross reactivity [28] , (Andrabi et al., submitted) . Presumably, the patients were infected with subtype-C viruses, which is a major subtype in India [64, 65] . Indeed, the envelope sequences (partial C2-C5 of envelope gp120) of a few patients revealed that majority of the patients were infected with subtype-C viruses (Andrabi et al., submitted) .