Mapping anti-gp41 responses. Panel A. Schematic representation of the antigens used for our fine mapping of anti-gp41 responses. Amino acid sequences of a recombinant full-length MIN protein and peptides C34 (gp41 aa 628–661), T20 (gp41 aa 638–673), OLP#19 (gp41 aa 671–684) and MPER (gp41 aa 659–683) are displayed. Panel B. Specific IgG titers for the recognition of MIN, MPER, T20, OLP#19 and C34 peptides by plasma samples. Titers are indicated in equivalents of 2F5 in ng/mL for MIN, T-20 and MPER or 4E10 equivalents in ng/ml for OLP#19. For C34 Arbitrary Units (AU) relative to one highly positive plasma sample used as standard are indicated. Panel C. Spearman´s correlation between standard anti-MPER ELISA assay and specific IgG signal displayed by 293-MIN cell line stained by plasma samples from HIV-1 infected individuals, anti-T20 ELISA titers, anti-C34 ELISA titers and anti-OLP#19 ELISA titers. Panel D. Plasma samples from HIV-1 infected individuals and healthy controls (HC) were tested in a competition assay by using the 293-MIN cell line and a fluorescently-labeled 2F5 antibody. The percentage of blockade of 2F5 binding is shown for both groups of samples. Correlations between 2F5 blockade and specific recognition of 293-MIN, 293-STAPLE and anti-MPER ELISA titers by plasma samples are shown. 2F5 competition assays and fine gp41-peptide mapping confirms the presence of anti-MPER antibodies in plasma from HIV-1 infected individuals. In panel B and D, ***denotes p < 0,001. In panels C and D the correlation coefficient (r) and p values (p) are shown.