Differential epitope recognition in the immunodominant staphylococcal antigen A of Staphylococcus aureus by mouse versus human IgG antibodies

The immunodominant staphylococcal antigen A (IsaA) is a potential target for active or passive immunization against the important human pathogen _Staphylococcus aureus_. Consistent with this view, monoclonal antibodies against IsaA were previously shown to be protective against _S. aureus_ infections in mouse models. Further, patients with the genetic blistering disease epidermolysis bullosa (EB) displayed high IsaA-specific IgG levels that could potentially be protective. Yet, mice actively immunized with IsaA were not protected against _S. aureus_ infection. The present study was aimed at explaining these differences in IsaA-specific immune responses. By epitope mapping, we show that the protective human monoclonal antibody (humAb) 1D9 recognizes a conserved 62-residue N-terminal domain of IsaA. The same region of IsaA is recognized by IgGs in EB patient sera. Further, we show by immunofluorescence microscopy that this N-terminal IsaA domain is exposed on the _S. aureus_ cell surface. In contrast to the humAb 1D9 and IgGs from EB patients, the non-protective IgGs from mice immunized with IsaA were shown to predominantly bind the C-terminal domain of IsaA. Altogether, these observations focus attention on the N-terminal region of IsaA as a potential target for future immunization against _S. aureus_

Genetic loci of Staphylococcus aureus associated with anti-neutrophil cytoplasmic autoantibody (ANCA)-associated vasculitides

The proteinase 3 (PR3)-positive anti-neutrophil cytoplasmic autoantibody (ANCA)-associated vasculitis (AAV) granulomatosis with polyangiitis (GPA) has been associated with chronic nasal S. aureus carriage, which is a risk factor for disease relapse. The present study was aimed at comparing the genetic make-up of S. aureus isolates from PR3-ANCA-positive GPA patients with that of isolates from patients suffering from myeloperoxidase (MPO)-ANCA-positive AAV, and isolates from healthy controls. Based on a DNA microarray-based approach, we show that not only PR3-ANCA-positive GPA patients, but also MPO-ANCA-positive AAV patients mainly carried S. aureus types that are prevalent in the general population. Nonetheless, our data suggests that MPO-ANCA-associated S. aureus isolates may be distinct from healthy control- and PR3-ANCA-associated isolates. Furthermore, several genetic loci of S. aureus are associated with either PR3-ANCA- or MPO-ANCA-positive AAV, indicating a possible role for pore-forming toxins, such as leukocidins, in PR3-ANCA-positive GPA. Contrary to previous studies, no association between AAV and superantigens was detected. Our findings also show that a lowered humoral immune response to S. aureus is common for PR3-ANCA- and MPO-ANCA-positive AAV. Altogether, our observations imply that the presence or absence of particular virulence genes of S. aureus isolates from AAV patients contributes to disease progression and/or relapse

Low anti-staphylococcal IgG responses in granulomatosis with polyangiitis patients despite long-term Staphylococcus aureus exposure

Chronic nasal carriage of the bacterium Staphylococcus aureus in patients with the autoimmune disease granulomatosis with polyangiitis (GPA) is a risk factor for disease relapse. To date, it was neither known whether GPA patients show similar humoral immune responses to S. aureus as healthy carriers, nor whether specific S. aureus types are associated with GPA. Therefore, this study was aimed at assessing humoral immune responses of GPA patients against S. aureus antigens in relation to the genetic diversity of their nasal S. aureus isolates. A retrospective cohort study was conducted, including 85 GPA patients and 18 healthy controls (HC). Humoral immune responses against S. aureus were investigated by determining serum IgG levels against 59 S. aureus antigens. Unexpectedly, patient sera contained lower anti-staphylococcal IgG levels than sera from HC, regardless of the patients' treatment, while total IgG levels were similar or higher. Furthermore, 210 S. aureus isolates obtained from GPA patients were characterized by different typing approaches. This showed that the S. aureus population of GPA patients is highly diverse and mirrors the general S. aureus population. Our combined findings imply that GPA patients are less capable of mounting a potentially protective antibody response to S. aureus than healthy individuals

Complementary impact of paralogous Oxa1-like proteins of Bacillus subtilis on post-translocational stages in protein secretion

In mitochondria, chloroplasts, and Gram-negative eubacteria, Oxa1p(-like) proteins are critical for the biogenesis of membrane proteins. Here we show that the Gram-positive eubacterium Bacillus subtilis contains two functional Oxalp orthologues, denoted SpoIIIJ and YqjG. The presence of either SpoIIIJ or YqjG is required for cell viability. Whereas SpoIIIJ is required for sporulation, YqjG is dispensable for this developmental process. The stability of two membrane proteins was found to be mildly affected upon SpoIIIJ limitation in the absence of YqjG. Surprisingly, the topology and stability of other membrane proteins remained unaffected under these conditions. In contrast, SpoIIIJ- and YqjG-limiting conditions resulted in a strong post-translocational defect in the stability of secretory proteins. Together, these data indicate that SpoIIIJ and YqjG of B. subtilis are involved in both membrane protein hiogenesis and protein secretion. However, the reduced stability of secretory proteins seems to be the most prominent phenotype of SpoIIIJ/YqjG-depleted B. subtilis cells. In conclusion, our observations show that SpoIIIJ and YqjG have different, but overlapping, functions in R subtilis. Most importantly, it seems that different members of the Oxalp protein family have acquired at least partly distinct, species-specific, functions that are essential for lif