Haekyung Lee

A dominant complement fixation pathway for pneumococcal polysaccharides initiated by SIGN-R1 interacting with C1q

The intricate system of serum complement proteins provides resistance to infection. A pivotal step in the complement pathway is the assembly of a C3 convertase, which digests the C3 complement component to form microbial binding C3 fragments recognized by leukocytes. The spleen and C3 provide resistance against blood-borne S. pneumoniae infection. To better understand the mechanisms involved, we studied SIGN-R1, a lectin that captures microbial polysaccharides in spleen. Surprisingly, conditional SIGN-R1 knockout mice developed deficits in C3 catabolism when given S. pneumoniae or its capsular polysaccharide intravenously. There were marked reductions in proteolysis of serum C3, deposition of C3 on organisms within SIGN-R1(+) spleen macrophages, and formation of C3 ligands. We found that SIGN-R1 directly bound the complement C1 subcomponent, C1q, and assembled a C3 convertase, but without the traditional requirement for either antibody or factor B. The transmembrane lectin SIGN-R1 therefore contributes to innate resistance by an unusual C3 activation pathway.

Cutting Edge: Langerin/CD207 Receptor on Dendritic Cells Mediates Efficient Antigen Presentation on MHC I and II Products In Vivo

The targeted delivery of Ags to dendritic cell (DCs) in vivo greatly improves the efficiency of Ag presentation to T cells and allows an analysis of receptor function. To evaluate the function of Langerin/CD207, a receptor expressed by subsets of DCs that frequently coexpress the DEC205/CD205 receptor, we genetically introduced OVA into the C terminus of anti-receptor Ab H chains. Taking advantage of the new L31 mAb to the extracellular domain of mouse Langerin, we find that the hybrid Ab targets appropriate DC subsets in draining lymph nodes and spleen. OVA is then presented efficiently to CD8+ and CD4+ T cells in vivo, which undergo 4–8 cycles of division in 3 days. Peptide MHC I and II complexes persist for days. Dose response studies indicate only modest differences between Langerin and DEC receptors in these functions. Thus, Langerin effectively mediates Ag presentation.

Broad T cell immunity to the LcrV virulence protein is induced by targeted delivery to DEC-205/CD205 positive mouse dendritic cells

There is a need for a more efficient vaccine against the bacterium Yersinia pestis, the agent of pneumonic plague. The F1‐LcrV (F1‐V) subunit vaccine in alhydrogel is known to induce humoral immunity. In this study, we utilized DC to investigate cellular immunity. We genetically engineered the LcrV virulence protein into the anti‐DEC‐205/CD205 mAb and thereby targeted the conjugated protein directly to mouse DEC‐205+ DC in situ. We observed antigen‐specific CD4+ T cell immunity measured by intracellular staining for IFN‐γ in three different mouse strains (C57BL/6, BALB/c, and C3H/HeJ), while we could not observe such T cell responses with F1‐V vaccine in alhydrogel. Using a peptide library for LcrV protein, we identified two or more distinct CD4+ T cell mimetopes in each MHC haplotype, consistent with the induction of broad immunity. When compared to nontargeted standard protein vaccine, DC targeting greatly increased the efficiency for inducing IFN‐γ‐producing T cells. The targeted LcrV protein induced antibody responses to a similar extent as the F1‐V subunit vaccine, but Th1‐dependent IgG2a and IgG2c isotypes were observed only after anti‐DEC‐205:LcrV mAb immunization. This study sets the stage for the analysis of functional roles of IFN‐γ‐producing T cells in Y. pestis infection.

Microbiota regulate the ability of lung dendritic cells to induce IgA class-switch recombination and generate protective gastrointestinal immune responses.

Ruane et al. demonstrate a role for the microbiota in modulating protective immunity to intranasal vaccination via the ability of lung dendritic cells to induce B cell IgA class switching.

Phenotype and function of nasal dendritic cells

Intranasal (i.n.) vaccination generates immunity across local, regional, and distant sites. However, nasal dendritic cells (DCs), pivotal for the induction of i.n. vaccine-induced immune responses, have not been studied in detail. Here, by using a variety of parameters, we define nasal DCs in mice and humans. Distinct subsets of “classical” DCs, dependent on the transcription factor zbtb46 were identified in the murine nose. The murine nasal DCs were Fms-related tyrosine 3 kinase ligand responsive and displayed unique phenotypic and functional characteristics, including the ability to present antigen, induce an allogeneic T-cell response, and migrate in response to lipopolysaccharide or live bacterial pathogens. Importantly, in a cohort of human volunteers, BDCA-1+ DCs were observed to be the dominant nasal DC population at steady state. During chronic inflammation, the frequency of both BDCA-1+ and BDCA-3hi DCs was reduced in the nasal tissue, associating the loss of these immune sentinels with chronic nasal inflammation. The present study is the first detailed description of the phenotypic, ontogenetic, and functional properties of nasal DCs, and will inform the design of preventative immunization strategies as well as therapeutic modalities against chronic rhinosinusitis.

Generation of anti-human DEC205/CD205 monoclonal antibodies that recognize epitopes conserved in different mammals

DEC205/CD205 is a C-type multilectin receptor, expressed highly in dendritic cells (DCs). Previous efforts to generate anti-human DEC205 (anti-hDEC205) monoclonal antibodies (mAbs) from mice immunized with subdomain proteins of hDEC205 resulted in a few mAbs. Recently, we expressed and utilized a full-length extracellular domain protein of hDEC205 to successfully generate 5 strong anti-hDEC205 mAbs from mice. In this study, DEC205 knockout (KO) mice were immunized with this full-length extracellular domain protein of hDEC205. One of the 3 immunized DEC205 KO mice was chosen for the highest anti-hDEC205 titer by flow cytometric analysis of serum samples on CHO cells stably expressing hDEC205 (CHO/hDEC205 cells) and used for hybridoma fusion. From a single fusion, more than 400 anti-hDEC205 hybridomas were identified by flow cytometric screen with CHO/hDEC205 cells, and a total of 115 hybridomas secreting strong anti-hDEC205 mAb were saved and named HD1 through HD115. To characterize in detail, 10 HD mAbs were chosen for superior anti-hDEC205 reactivity and further subjected to cloning and purification. Interestingly, out of those 10 chosen anti-hDEC205 HD mAbs, 5 mAbs were also strongly reactive to mouse DEC205 while 8 mAbs were found to stain DEC205(+) DCs on monkey spleen sections. In addition, we also identified that HD83, one of the 10 chosen HD mAbs, stains DEC205(+) DCs in rat spleen and lymph node. Therefore, by immunizing DEC205 KO mice with a full-length extracellular domain protein of hDEC205, we generated a large number of strong anti-hDEC205 mAbs many of which are cross-species reactive and able to visualize DEC205(+) DCs in lymphoid tissues of other mammals.

Secreted IgD Amplifies Humoral T Helper 2 Cell Responses by Binding Basophils via Galectin-9 and CD44

Graphical Abstract Figure. No caption available. SUMMARY B cells thwart antigenic aggressions by releasing immunoglobulin M (IgM), IgG, IgA, and IgE, which deploy well‐understood effector functions. In contrast, the role of secreted IgD remains mysterious. We found that some B cells generated IgD‐secreting plasma cells following early exposure to external soluble antigens such as food proteins. Secreted IgD targeted basophils by interacting with the CD44‐binding protein galectin‐9. When engaged by antigen, basophil‐bound IgD increased basophil secretion of interleukin‐4 (IL‐4), IL‐5, and IL‐13, which facilitated the generation of T follicular helper type 2 cells expressing IL‐4. These germinal center T cells enhanced IgG1 and IgE but not IgG2a and IgG2b responses to the antigen initially recognized by basophil‐bound IgD. In addition, IgD ligation by antigen attenuated allergic basophil degranulation induced by IgE co‐ligation. Thus, IgD may link B cells with basophils to optimize humoral T helper type 2‐mediated immunity against common environmental soluble antigens. HIGHLIGHTSIgD interacts with basophils through the CD44‐binding protein galectin‐9IgD ligation by antigen elicits basophil release of Th2 cell‐associated cytokinesIgD‐activated basophils enhance B cell production of IgG1 and IgEIgD interferes with IgE‐mediated basophil degranulation &NA; The function of IgD has been mysterious. Shan et al. find that IgD recognized food antigens and targeted basophils through galectin‐9. IgD ligation by antigen induced basophil secretion of IL‐4, IL‐5, and IL‐13, which amplified Th2 cell‐mediated IgG1 and IgE production by B cells. IgD also constrained IgE‐mediated basophil degranulation.

The Relationship Between Injection Drug Use Risk Behaviors and Markers of Immune Activation

Abstract: High levels of immune activation are reported for people who inject drugs. Studies of the relationship between injection behaviors and immune activation have yielded mixed results, in part due to lack of control for hepatitis C virus in analyses. This study, of 48 HIV-seronegative people who inject drugs, examines this relationship controlling for hepatitis C virus viremia. Frequency of injection was positively related to markers of immune activation (soluble CD14, %CD8+CD38+HLADR+ T cells), as was duration of injection (high-specificity C-reactive protein and D-dimer). Sharing injection equipment was not related to markers studied. Findings suggest that efforts to encourage injection cessation or reduction in frequency can have positive health benefits through reducing immune activation.