Secretory IgA Specific for a Conserved Epitope on gp41 Envelope Glycoprotein Inhibits Epithelial Transcytosis of HIV-1

Abstract

As one of the initial mucosal transmission pathways of HIV (HIV-1), epithelial cells translocate HIV-1 from apical to basolateral surface by nondegradative transcytosis. Transcytosis is initiated when HIV-1 envelope glycoproteins bind to the epithelial cell membrane. Here we show that the transmembrane gp41 subunit of the viral envelope binds to the epithelial glycosphingolipid galactosyl ceramide (Gal Cer), an alternative receptor for HIV-1, at a site involving the conserved ELDKWA epitope. Disrupting the raft organization of the Gal Cer-containing microdomains at the apical surface inhibited HIV-1 transcytosis. Immunological studies confirmed the critical role of the conserved ELDKWA hexapeptide in HIV-1 transcytosis. Mucosal IgA, but not IgG, from seropositive subjects targeted the conserved peptide, neutralized gp41 binding to Gal Cer, and blocked HIV-1 transcytosis. These results underscore the important role of secretory IgA in designing strategies for mucosal protection against HIV-1 infection.

Intraepithelial Cell Neutralization of HIV-1 Replication by IgA

“…With respect to HIV, IgA (and IgM) Abs placed at either the apical or basolateral surface have been reported to block transcytosis of virus from the apical to the basolateral side in a tight epithelial cell monolayer (16,24,(33)(34)(35)(36). These findings suggest that in vivo HIV-specific IgA can both exclude HIV from mucosal epithelial cells and prevent transcytosing HIV from spreading to the lamina propria, where abundant T cells and macrophages are potential targets of infection.…”

A mucosally targeted subunit vaccine candidate eliciting HIV-1 transcytosis-blocking Abs

“…GalCer blot analysis was carried out as described (11). Sandwich or G M1 ELISA was done essentially as described (34) by using anti-CT Ab (Sigma) or G M1 (Sigma-Aldrich), respectively, for capture.…”

“…[12][13][14]. In addition to direct targeting of HIV-1 by neutralizing Abs (15), HIV-1 transcytosis can be blocked by disruption of rafts and by Abs against the ELDKWA epitope (7,8,10,11).…”

“…Recently, the GalCer-binding domain of gp41 was mapped to a highly conserved, partially ␣-helical region of gp41 (''P1'' peptide, residues 649-684, Fig. 1), extending between the gp120 cap and the transmembrane domain (9)(10)(11). This domain spans conserved epitopes including the ELDKWA (''Katinger'') sequence, the target of the broadly neutralizing human monoclonal IgG, 2F5 ( Fig.…”

Intranasal HIV-1-gp160-DNA/gp41 Peptide Prime-Boost Immunization Regimen in Mice Results in Long-Term HIV-1 Neutralizing Humoral Mucosal and Systemic Immunity

“…They compared 862 HIV-1 strains and showed that 90 -97% of the isolates contain the LQAR sequence in the coiled-coil region, whereas the LELDKWAS region showed a more variable mix of 50 -97% conserved amino acids (with amino acids L-LD-W being Ͼ97% conserved). This combination of epitopes included in a vaccine may provide the conserved epitopes that have been so difficult to find in other regions of the HIV-1 envelope even though highly conserved cross-neutralization Ab-inducing epitopes have been described in the gp120 V3 region aa GPGR (47)(48)(49) and within the CD4-binding region of gp120 (50). Additional evidence suggesting the importance of inducing Abs against these gp41 epitopes is the low frequency of Ab reactivities against these regions in HIV-infected individuals (51).…”