Most potential linear B cell epitopes of Env glycoproteins of feline immunodeficiency virus are immunogenically silent in infected cats.

A battery of sixty-six 20- to 23-amino acid synthetic peptides, partially overlapping by 10-12 amino acids, spanning the entire sequence of the envelope (Env) glycoproteins of the Petaluma isolate of feline immunodeficiency virus (FIV-Pet), has been used to map Env linear B cell epitopes. By screening FIV-infected cat sera for anti-peptide reactivity, the existence of two immunodominat domains, namely the V3 region of the surface (SU) glycoprotein and the domain including the highly conserved sequence QNQFF of the transmembrane (TM) glycoprotein, was detected; antibody-binding sites were also mapped in the domain overlapping the cleavage site between SU and TM encompassing the V6 variable region. Moreover, at least two novel linear B epitopes, the former spanning residues 427M-H446 and the latter spanning residues 737N-N756 and likely representing a "type-specific" determinant, have been revealed. The battery of synthetic peptides was then used to immunize outbred Swiss mice in the attempt to reveal other potential sites of immunogenicity of the Env glycoproteins. Analysis of peptide-immunized mouse sera for anti-peptide reactivity revealed more numerous B cell epitopes, generally mapping in different peptides, as compared with those defined in the feline system. None of the mouse anti-peptide sera, however, proved neutralizing for FIV-Pet.

The antiviral activity of a synthetic peptide derived from the envelope SU glycoprotein of feline immunodeficiency virus maps in correspondence of an amphipathic helical segment.

In a previous paper (Lombardi et al., Virology 220, 274-284, 1996), we-reported that a 20-amino acid synthetic peptide derived from a conserved region of the SU glycoprotein of feline immunodeficiency virus (FIV), i.e., 225EGPTLGNWAREIWATLFKKA244, bound the surface of FIV-permissive cells and inhibited FIV infection of CrFK and lymphoid cells. In this paper, we report, by the use of N- and C-terminus deleted synthetic analogs and by glycine scanning experiments that the minimal sequence needed for the full antiviral activity of the peptide maps in correspondence of amino acids 229LGNWAREIWATL240 and that either tryptophans residues at sequence position 232 or 237 are essential for such activity. Circular dichroism (CD) studies indicate that in the presence of a hydrophobic environment the 225E-A244 peptide adopts a structure containing an amphipathic alpha-helical segment of approximately 7 residues, corresponding to 2 helical turns, likely in correspondence of the sequence 231(N)WAREIW(A)238. Such a helical segment of FIV SU glycoprotein may play a role in viral envelope fusion role with the host cell membrane, thus proving critical for cell infection.

Inhibition of feline immunodeficiency virus infection in vitro by envelope glycoprotein synthetic peptides.

Sixty-six 20- to 23-amino-acid synthetic peptides, partially overlapping by 10-12 amino acids, spanning the entire sequence of the envelope SU and TM glycoproteins of the Petaluma isolate of FIV, have been used to investigate the Env domains involved in viral infection. Peptides 5 to 7, spanning amino acids 225E-P264 located in a conserved region of the SU protein, and peptides 58 to 61, spanning amino acids 767N-P806 and encompassing hypervariable region 8 of TM protein, exhibited a remarkable and specific antiviral effect against the homologous and one heterologous isolate, as judged by inhibition of FIV-induced syncytium formation and p25 production in CrFK cells. Peptides 5 and 7, but not peptides 58 and 59, also inhibited viral replication of a fresh FIV isolate on nontransformed lymphoid cells. By flow cytometry, peptides 5, 7, 58, and 59 were shown to bind the surface of FIV permissive cells. The antiviral activity of peptides 5 and 7, however, was time-dependent, as inhibition of FIV replication was seen when the peptides were administered before or within 3 hr after virus inoculation; in contrast, TM peptides 58 and 59 exerted a potent inhibitory effect when added up to 24 hr after virus inoculation. Circular dychroism analysis showed that peptide 5 folds to a helical conformation in the presence of a hydrophobic environment. Although the basis for the antiviral action of the peptides is not understood, our data suggest that the inhibitory peptides may act by interacting with cell-surface molecules involved in viral infection.