Maternal Anti-Dengue IgG Fucosylation Predicts Susceptibility to Dengue Disease in Infants

Infant mortality from dengue disease is a devastating global health burden that could be minimized with the ability to identify susceptibility for severe disease prior to infection. Although most primary infant dengue infections are asymptomatic, maternally derived anti-dengue immunoglobulin G (IgGs) present during infection can trigger progression to severe disease through antibody-dependent enhancement mechanisms. Importantly, specific characteristics of maternal IgGs that herald progression to severe infant dengue are unknown. Here, we define \u3e /=10% afucosylation of maternal anti-dengue IgGs as a risk factor for susceptibility of infants to symptomatic dengue infections. Mechanistic experiments show that afucosylation of anti-dengue IgGs promotes FcgammaRIIIa signaling during infection, in turn enhancing dengue virus replication in FcgammaRIIIa(+) monocytes. These studies identify a post-translational modification of anti-dengue IgGs that correlates with risk for symptomatic infant dengue infections and define a mechanism by which afucosylated antibodies and FcgammaRIIIa enhance dengue infections

tmRNA is essential in Shigella flexneri.

Nonstop mRNAs pose a challenge for bacteria, because translation cannot terminate efficiently without a stop codon. The trans-translation pathway resolves nonstop translation complexes by removing the nonstop mRNA, the incomplete protein, and the stalled ribosome. P1 co-transduction experiments demonstrated that tmRNA, a key component of the trans-translation pathway, is essential for viability in Shigella flexneri. tmRNA was previously shown to be dispensable in the closely related species Escherichia coli, because E. coli contains a backup system for trans-translation mediated by the alternative release factor ArfA. Genome sequence analysis showed that S. flexneri does not have a gene encoding ArfA. E. coli ArfA could suppress the requirement for tmRNA in S. flexneri, indicating that tmRNA is essential in S. flexneri because there is no functional backup system. These data suggest that resolution of nonstop translation complexes is required for most bacteria

ArfA is expressed in cells containing <i>pCA24N-His₆-ArfA</i>.

<p>(<b>A</b>) Western blots to determine the expression of ArfA in wild-type <i>S. flexneri</i> (lane 1), <i>S. flexneri ssrA::kan pCA24N-His₆-ArfA</i> grown with IPTG at all times (lane 2), grown without IPTG and diluted into medium containing IPTG (lane 3), and grown without exposure to IPTG (lane 4). The amounts of ArfA relative to lane 3 are shown (n.d.: not detectable). (<b>B</b>) Growth of <i>S. flexneri ssrA::kan pCA24N-His₆-ArfA</i> with IPTG (closed circles) and with no IPTG (open circles) monitored by optical density at 600 nm. Doubling times during exponential growth (80–160 min) are indicated.</p

<i>arfA</i> accounts for phenotypic differences produced by deleting <i>ssrA</i> in <i>E. coli</i> and <i>S. flexneri.</i>

<p>(<b>A</b>) <i>arfA</i> (blue) in <i>Escherichia coli K-12 MG1655</i> and the corresponding locus in <i>Shigella flexneri</i> 2a 2457T, aligned using EcoCyc Pathway Tools (SRI International). (<b>B</b>) Diagnostic PCR reactions of genomic DNA prepared from wild-type <i>S. flexneri</i> (lane 1), <i>S. flexneri pCA24N-His₆-ArfA</i> (lane 2), and <i>S. flexneri ssrA::kan pCA24N-His₆-ArfA</i> (lane 3). The expected product size for wild-type <i>ssrA</i> is 0.6 kb and for <i>ssrA::kan</i> is 1.7 kb. Molecular weight markers with sizes in kb are indicated.</p

Strains, plasmids and primers used in this study.

<p>Strains, plasmids and primers used in this study.</p

<i>ssrA</i> is dispensible in <i>S. flexneri</i> when a second copy of the gene is provided.

<p>Diagnostic PCR reactions were used to verify deletion of <i>ssrA</i> in <i>S. flexneri ssrA::kan pSsrA</i>. The expected product size for wild-type <i>ssrA</i> is 0.6 kb and for <i>ssrA::kan</i> is 1.7 kb. A control reaction using genomic DNA from wild-type <i>S. flexneri</i> and molecular weight markers with sizes in kb are indicated.</p

Identification of HIV gp41-specific antibodies that mediate killing of infected cells.

Antibodies that mediate killing of HIV-infected cells through antibody-dependent cellular cytotoxicity (ADCC) have been implicated in protection from HIV infection and disease progression. Despite these observations, these types of HIV antibodies are understudied compared to neutralizing antibodies. Here we describe four monoclonal antibodies (mAbs) obtained from one individual that target the HIV transmembrane protein, gp41, and mediate ADCC activity. These four mAbs arose from independent B cell lineages suggesting that in this individual, multiple B cell responses were induced by the gp41 antigen. Competition and phage peptide display mapping experiments suggested that two of the mAbs target epitopes in the cysteine loop that are highly conserved and a common target of HIV gp41-specific antibodies. The amino acid sequences that bind these mAbs are overlapping but distinct. The two other mAbs were competed by mAbs that target the C-terminal heptad repeat (CHR) and the fusion peptide proximal region (FPPR) and appear to both target a similar unique conformational epitope. These gp41-specific mAbs mediated killing of infected cells that express high levels of Env due to either pre-treatment with interferon or deletion of vpu to increase levels of BST-2/Tetherin. They also mediate killing of target cells coated with various forms of the gp41 protein, including full-length gp41, gp41 ectodomain or a mimetic of the gp41 stump. Unlike many ADCC mAbs that target HIV gp120, these gp41-mAbs are not dependent on Env structural changes associated with membrane-bound CD4 interaction. Overall, the characterization of these four new mAbs that target gp41 and mediate ADCC provides evidence for diverse gp41 B cell lineages with overlapping but distinct epitopes within an individual. Such antibodies that can target various forms of envelope protein could represent a common response to a relatively conserved HIV epitope for a vaccine

Cytotoxic CD8+ T cells target citrullinated antigens in rheumatoid arthritis

The immune mechanisms underlying synovitis and joint tissue destruction in rheumatoid arthritis (RA) remain incompletely defined. Here, the authors demonstrate that ACPA+ RA patients have activated clonally expanded cytotoxic GZMB+ CD8+ T cells in blood and synovium that target and are activated by citrullinated antigens to mediate cell killing