Anti-inflammatory activity of human IgA antibodies and their Fab alpha fragments: inhibition of IgG-mediated complement activation

Serum IgA subclasses and molecular forms in HIV infection: selective increases in monomer and apparent restriction of the antibody response to IgA1 antibodies mainly directed at env glycoproteins

In a study population representing different CDC stages of HIV infection, 58% exhibited IgA hypergammaglobulinemia resulting from proportional increases in both the IgA1 and the IgA2 subclasses. These increases were detected early in infection, did not correlate with CD4 count, and remained elevated throughout disease progression. Absolute concentrations of polymeric IgA present within each subclass were unchanged, indicating that increased production of monomeric IgA1 and IgA2 were responsible for elevations of total IgA. These elevations were not completely attributable to a specific antibody response to viral infection, since Western blot analysis of purified IgA samples indicated that HIV-reactive IgA antibodies could be demonstrated only within the IgA1 subclass. Dominating IgA1 anti-HIV responses were also observed in two secretory IgA samples isolated from colostrum of healthy HIV seropositive mothers, suggesting that a similar isotype restriction exists in the mucosal IgA compartment. The binding of IgA1 to HIV proteins contrasted markedly to that observed with identical concentrations of IgG purified from the sera of the same patients. While IgG reacted more intensely and broadly with all HIV proteins, IgA1 antibodies were directed predominantly against envelope glycoproteins. In many patients, a total lack of IgA1 reactivity to gag and pol proteins was accompanied by intact IgG responses to these same antigens. Though all IgA samples examined reacted with HIV, fewer responses to gp160, gp120, and p24 were observed in samples from AIDS and AIDS-related complex (ARC) patients, suggesting a declining titer of IgA antibodies against these antigens may be associated with disease progression.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of the immunoglobulin A protease gene of Streptococcus sanguis

The amino acid sequence T-P-P-T-P-S-P-S is tandemly duplicated in the heavy chain of human immunoglobulin A1 (IgA1), the major antibody in secretions. The bacterial pathogen Streptococcus sanguis, a precursor to dental caries and a cause of bacterial endocarditis, yields IgA protease that cleaves only the Pro-Thr peptide bond in the left duplication, while the type 2 IgA proteases of the genital pathogen Neisseria gonorrhoeae and the respiratory pathogen Haemophilus influenzae cleave only the P-T bond in the right half. We have sequenced the entire S. sanguis iga gene cloned into Escherichia coli. A segment consisting of 20 amino acids tandemly repeated 10 times, of unknown function, occurs near the amino-terminal end of the enzyme encoded in E. coli. Identification of a predicted zinc-binding region in the S. sanguis enzyme and the demonstration that mutations in this region result in production of a catalytically inactive protein support the idea that the enzyme is a metalloprotease. The N. gonorrhoeae and H. influenzae enzymes were earlier shown to be serine-type proteases, while the Bacteroides melaninogenicus IgA protease was shown to be a cysteine-type enzyme. The streptococcal IgA protease amino acid sequence has no significant homology with either of the two previously determined IgA protease sequences, that of type 2 N. gonorrhoeae and type 1 H. influenzae. The differences in both structure and mechanism among these functionally analogous enzymes underscore their role in the infectious process and offer some prospect of therapeutic intervention.