No abstract

Antibody hydrolysis of the superantigenic gp120 site and HIV-1 neutralization was studied as a potential anti-HIV mechanism in uninfected humans. gp120 hydrolysis by purified serum and salivary antibodies was determined by electrophoresis and peptide sequencing, the proteolytic mechanism was analyzed using electrophilic peptide analogs, and viral neutralization was studied using peripheral blood mononuclear cells as hosts. Polyclonal and monoclonal IgA but not IgG preparations selectively catalyzed the cleavage of HIV gp120 at rates sufficient to predict biologically relevant protection against the virus. The IgA hydrolytic reaction proceeded by noncovalent recognition of gp120 residues 421-433, a component of the superantigenic site of gp120, coordinated with peptide bond cleavage via a serine protease-like mechanism. The Lys-432-Ala-433 bond was one of the cleavage sites. Infection of peripheral blood mononuclear cells by a primary isolate of HIV was neutralized by the IgA but not IgG fractions. The neutralizing activity was specifically inhibited by an electrophilic inhibitor of the catalytic activity. The existence of catalytic IgAs to gp120 in uninfected humans suggests their role in resistance to HIV.

Objective-To identify an HIV epitope suitable for vaccine development.Design-Diverse HIV-1 strains express few structurally constant regions on their surface vulnerable to neutralizing antibodies. The mostly-conserved CD4 binding site (CD4BS) of gp120 is essential for host cell binding and infection by the virus. Antibodies that recognize the CD4BS are rare, and one component of the CD4BS, the 421-433 peptide region, expresses B cell superantigenic character, a property predicted to impair the anti-CD4BS adaptive immune response.Methods-IgA samples purified from the plasma of subjects with HIV infection were analyzed for the ability to bind synthetic mimetics containing the 416-433 gp120 region and full-length gp120. Infection of peripheral blood mononuclear cells by clinical HIV isolates was measured by p24 ELISA.Results-IgA preparations from 3 subjects with subtype B infection for 19-21 years neutralized heterologous, coreceptor CCR5-dependent subtype A, B, C, D and AE strains with exceptional potency. The IgAs displayed specific binding of a synthetic 416-433 peptide mimetics dependent on recognition of the CD4 binding residues located in this region. Immunoadsorption, affinity chromatography and mutation procedures indicated that HIV neutralization occurred by IgA recognition of the CD4BS. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Background: Some antibodies express serine protease activity. Transthyretin misfolding causes accumulation of pathogenic amyloid. Results: Constitutively produced IgM but not IgG class antibodies selectively hydrolyzed and dissolved misfolded transthyretin without hydrolyzing physiologically folded transthyretin. Some IgMs were oligoreactive with amyloids and superantigens. Conclusion: Catalytic IgMs may clear misfolded TTR and delay amyloidosis. Significance: The innate antibody repertoire is a source of selective catabodies to toxic proteins.

A monoclonal antibody (MAb), ECL2B-2, was obtained by immunizing a peptide possessing a part of a sequence of a chemokine receptor, CCR-5, which is present as a membrane protein on the macrophage surface, and which plays an important role in human immunodeficiency virus (HIV) infection. From the DNA and the deduced amino acid sequences of the light and heavy chains of ECL2B-2 MAb, molecular modeling was conducted to calculate the steric conformation of the antibody. Modeling suggested that the structure of ECL2B-2 could possess one or two catalytic triad(s), composed of Asp(1), Ser(27a) (or Ser(27e)), and His(93) (or His(27d)), in the light chain of ECL2B-2. The three amino acid residues, Asp(1), Ser(27a), and His(93), are identical to those of catalytic antibody light chains such as VIPase and i41SL1-2. The light chain of ECL2B-2 MAb degraded the antigenic peptide CCR-5 within about 100 h. Surprisingly, the light chain had a very high catalytic reaction rate constant (k(cat)) of 2.23 min(-1), which is greater by factors of tens to hundreds than those of natural catalytic antibodies obtained previously. The heavy chain of ECL2B-2 MAb, which has no catalytic triad because of a lack of His residue, did not degrade the CCR-5 peptide.