The immunosuppressive peptide of HIV-1 inhibits T and B lymphocyte stimulation.

The transmembrane glycoproteins of all retroviruses contain a conserved region composed of a leucine zipper, an immunosuppressive domain, and an immunodominant Cys-Cys loop. The amino acid sequence of the immunosuppressive domain of gp41 of human immunodeficiency virus type 1 (HIV-1; amino acids 583-599) is closely related, but not identical, to the immunosuppressive domains of type C and D retroviruses. A synthetic peptide corresponding to the immunosuppressive domain of HIV-1 (immunosuppressive peptide, ISU-peptide) inhibits mitogen and lymphokine stimulation of T lymphocytes. It is interspecies reactive and inhibits both human and mouse lymphocytes. The inhibitory effect is not based on direct cytotoxicity and the peptide is immunosuppressive only when conjugated to a carrier protein. The ISU-peptide of HIV-1 also inhibits B lymphocyte stimulation by the B cell mitogen lipopolysaccharide and by specific antibodies against delta and mu chains of cell surface immunoglobulins. These data suggest that the immunosuppressive domain of gp41 may play an important role in the immunopathogenesis of AIDS.