To probe such antibodies in the CNsera, we analysed

the serum antibody reactivity with synthetic peptides containing the epitopes of 2F5 and 4E10, respectively (Amino acid sequences were shown in Table 1). As is shown in Fig. 1C, bNAbs 2F5 and 4E10 only reacted with peptides containing their specific epitopes, respectively. In eight CNsera, only Serum 15 showed high reactivity with both 2F5 and 4E10 peptides (Fig. 1C), suggesting the presence of both 2F5- and 4E10-like antibodies. DAPT clinical trial To determine whether these antibodies mediated the cross-clade neutralizing activity, we analysed the neutralization of Serum 15 in the presence of either 2F5 or 4E10 peptides as competitors. 2F5 and 4E10 peptides inhibited about 20% and 60% neutralizing activities of Serum 15 against CNE40, respectively, but neither peptide inhibited

the neutralizing activity of Serum 15 against JRFL (Table 5), an isolate sensitive to both 2F5 and 4E10 antibodies. In contrast, 3 μm 2F5 peptide completely inhibited the neutralization of 2F5 against JRFL and 9 μm 4E10 peptide completely inhibited the neutralization of 4E10 against CNE40, respectively (Figure S1). We therefore concluded that 2F5- or 4E10-like antibodies are rare in those sera and the 2F5- or 4E10-like antibodies in Serum 15 were unlikely the major contributor for the cross-neutralizing Caspase inhibition activity of the serum. V3-specific antibodies Phospholipase D1 are induced early and persist during the course of infection. The sequence-specific nature of the antibodies

and their type-specific neutralization are well documented in the sera of clade B virus-infected individuals although broadly neutralizing antibodies, such as 447-52D, have been isolated. Therefore, we analysed the V3-specific antibodies in the Chinese CNsera and their potential roles in serum neutralization. First, we examined the reactivity of CNsera against three sets of linear V3 peptides derived from three primary isolates: JRFL V3 (JV3), CNE6 V3 (6V3) and CNE55 V3 (55V3) (Fig. 1D) whose amino acid sequences were shown in Table 1. No serum reacted with 6V3 that carries a rare GLGR sequence at its tip, and all eight CNsera reacted with JV3 which has a GPGR sequence at the tip. In addition, all sera except 8 and 29 reacted with 55V3 that expresses a GPGQ sequence at the tip of the region. To determine whether the V3-reactive antibodies in CNsera contributed to neutralizing activities, competition neutralization assays were performed by preincubating CNsera with either JV3 or 55V3 peptide to block the V3 peptide-reactive antibodies. At 3 μm, JV3 could completely inhibit the neutralizing activity of 447-52D against CNE40, but 55V3 could only partially inhibit it (Figure S2).