(ClinicalTrials.Gov) identifiers: NCT00197691 and NCT00197652.

Invasive infection often begins with asymptomatic colonization of mucosal surfaces. A murine model of bacterial colonization with Streptococcus pneumoniae was used to study the mechanism for mucosal protection by immunoglobulin. In previously colonized immune mice, bacteria were rapidly sequestered within large aggregates in the nasal lumen. To further examine the role of bacterial agglutination in protection by specific antibodies, mice were passively immunized with IgG purified from anti-pneumococcal sera or pneumococcal type-specific monoclonal human IgA (hIgA1 or hIgA2). Systemically-delivered IgG accessed the mucosal surface and blocked acquisition of colonization and transmission between littermates. Optimal protection by IgG was independent of Fc fragment and complement and, therefore, did not involve an opsonophagocytic mechanism. Enzymatic digestion or reduction of IgG prior to administration showed that protection required divalent binding that maintained its agglutinating effect. Divalent hIgA1 is cleaved by the pneumococcal member of a family of bacterial proteases that generate monovalent Fabα fragments. Thus, passive immunization with hIgA1 blocked colonization by an IgA1-protease deficient mutant (agglutinated), but not the protease-producing wild-type parent (not agglutinated), whereas protease-resistant hIgA2 agglutinated and blocked colonization by both. Our findings highlight the importance of agglutinating antibodies in mucosal defense and reveal how successful pathogens evade this effect.

Bacterial IgA1 proteases may sabotage the protective effects of IgA. In vitro, both exogenous and endogenously-produced IgA1 protease inhibited phagocytic killing of Streptococcus pneumoniae by capsule-specific IgA1 human monoclonal antibodies (hMAb's), but not IgA2. These IgA1 proteases cleaved and reduced binding of the the effector Fcα1 heavy chain but not the antigen-binding F(ab)/light chain to pneumococcal surfaces. In vivo, IgA1 protease-resistant IgA2, but not IgA1 protease-sensitive IgA1, supported 60% survival in mice infected with wild-type S. pneumoniae. IgA1 hMAb's protected mice against IgA1 protease-deficient, but not -producing pneumococci. Parallel mouse sera with human IgA2 showed more efficient complement-mediated reductions in pneumococci with neutrophils than did IgA1, particularly with protease-producing organisms. After natural human pneumococcal bacteremia, purified serum IgG inhibited IgA1 protease activity in 7 of 11 patients (64%). These observations provide the first evidence in vivo that IgA1 protease can circumvent killing of S. pneumoniae by human IgA. Acquisition of IgA1 protease-neutralizing IgG after infection directs attention to IgA1 protease both as a determinant of successful colonization and infection and as a potential vaccine candidate.

Background The risk of pneumococcal disease persists and antibody responses to revaccination with the 23-valent polysaccharide vaccine (PPV) are low among HIV-infected adults. We determined whether revaccination with the 7-valent pneumococcal conjugate vaccine (PCV) would enhance these responses. Methods In a randomized clinical trial, we compared the immunogenicity of revaccination with PCV (n=131) or PPV (n=73) among HIV-infected adults (median CD4 count 533 cells/mm3) vaccinated with PPV 3–8 years earlier. HIV-uninfected adults (n=25) without prior pneumococcal vaccination received one dose of PCV. A positive response was defined as a ≥2-fold rise (baseline to day 60) in capsule-specific IgG with a post-vaccination level value ≥1000 ng/ml for at least 2 of the 4 serotypes. Results HIV-infected persons demonstrated a higher frequency of positive antibody responses to PCV vs. PPV (57% vs. 36%, p=0.004) and greater IgG concentration mean changes from baseline to day 60 for serotypes 4, 9V, and 19F (all p<0.05), but not for serotype 14. However by day 180 both outcomes were similar. Responses to PCV were greater in frequency and magnitude for all serotypes in HIV-uninfected compared with those in HIV-infected adults. Conclusions Among persons with HIV infection, revaccination with PCV was only transiently more immunogenic than PPV, and responses were inferior to those in HIV-uninfected subjects with primary vaccination. Pneumococcal vaccines with more robust and sustained immunogenicity are needed for HIV-infected adults.

Purpose: Several observations suggest the presence of HIV-suppressive factors in the fluid phase of blood. Alpha-1-antitrypsin (AAT), the most abundant serine protease inhibitor in the circulation, has potent anti-HIV activity in vitro, and may function as an endogenous HIV suppressor. Therefore, we assessed serum AAT concentrations for association with HIV infection. Methods: In this cross-sectional study, serum AAT concentrations were measured in 66 persons with HIV infection and in 45 healthy persons (Controls). In the HIV-infected group, antiretroviral therapy (ART) use was assessed and CD4+ T cell levels and plasma HIV RNA were quantified. Results: Median AAT concentration was significantly lower in the HIV-infected group (1.64 mg/mL) in comparison with Controls (1.94 mg/mL; p=0.001). AAT reduction was most pronounced in the HIV-infected subgroup with CD4+ T cell levels > 200 cells/µL in comparison with Controls (p < 0.01). Serum AAT concentrations < 1.0 mg/mL are clinically significant, and concentrations below this level were identified in 4.5% of the HIV-infected group and in no Control subjects. No association between AAT levels and viral load or use of ART was observed in HIV-infected subjects. Conclusion: The association between reduced serum AAT concentration and HIV infection is consistent with a role for AAT as an endogenous HIV suppressor.

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IgA1 proteases (IgA1P) from diverse pathogenic bacteria specifically cleave human immunoglobulin A1 (IgA1) at the hinge region, thereby thwarting protective host immune responses. Streptococcus pneumoniae (S. pneumoniae) IgA1P shares no sequence conservation with serine or cysteine types of IgA1Ps or other known proteins, other than a conserved HExxH Zn-binding motif (1604-1608) found in metalloproteases. We have developed a novel expression system to produce the mature S. pneumoniae IgA1P and we have discovered that this form is both attached to the bacterial cell surface and released in its full form. Our data demonstrate that the S. pneumoniae IgA1P comprises two distinct regions that associate to form an active metalloprotease, the first such example of a metalloprotease that can be split in vitro and recombined to form an active enzyme. By capitalizing on this novel domain architecture, we show that the N-terminal region of S. pneumoniae IgA1P comprises the primary binding region for IgA1, although the C-terminal region of S. pneumoniae IgA1P is necessary for cleavage of IgA1. Our findings lend insight into the protein domain architecture of the S. pneumoniae IgA1P and function of this important virulence factor for S. pneumoniae infection.

Breast milk is a vehicle of infection and source of protection in post-natal mother-to-child HIV-1 transmission (MTCT). Understanding the mechanism by which breast milk limits vertical transmission will provide critical insight into the design of preventive and therapeutic approaches to interrupt HIV-1 mucosal transmission. However, characterization of the inhibitory activity of breast milk in human intestinal mucosa, the portal of entry in postnatal MTCT, has been constrained by the limited availability of primary mucosal target cells and tissues to recapitulate mucosal transmission ex vivo. Here, we characterized the impact of skimmed breast milk, breast milk antibodies (Igs) and non-Ig components from HIV-1-infected Ugandan women on the major events of HIV-1 mucosal transmission using primary human intestinal cells and tissues. HIV-1-specific IgG antibodies and non-Ig components in breast milk inhibited the uptake of Ugandan HIV-1 isolates by primary human intestinal epithelial cells, viral replication in and transport of HIV-1- bearing dendritic cells through the human intestinal mucosa. Breast milk HIV-1-specific IgG and IgA, as well as innate factors, blocked the uptake and transport of HIV-1 through intestinal mucosa. Thus, breast milk components have distinct and complementary effects in reducing HIV-1 uptake, transport through and replication in the intestinal mucosa and, therefore, likely contribute to preventing postnatal HIV-1 transmission. Our data suggests that a successful preventive or therapeutic approach would require multiple immune factors acting at multiple steps in the HIV-1 mucosal transmission process.