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Fc receptor–like (FCRL) 4 is an immunoregulatory receptor expressed on a subpopulation of human memory B cells of mucosa-associated lymphoid tissue. Fc receptor function of FCRL4 was demonstrated by binding of IgA to FCRL4 following heat aggregation of the Ig. In this study, we demonstrate that FCRL4 recognizes J chain–linked systemic IgA in the absence of heat aggregation. We further demonstrate that mucosal secretory IgA is not recognized by FCRL4 and that systemic IgA binding can be competitively inhibited by recombinant secretory component protein. Finally, we provide evidence that primary FCRL4-bearing human memory B cells are constitutively bound to IgA. Our study provides a mechanism for the negative regulatory activity of FCRL4 on AgR-mediated B cell activation.

CD38 is a multifunctional cell surface receptor expressed on multiple cell lineages of hematopoietic origin with high levels of expression on human plasma cells. Previously, we isolated the monoclonal variable lymphocyte receptor B (VLRB) MM3 antibody from the evolutionarily distant sea lamprey, which recognized the CD38 ectoenzyme exclusively on human plasma cells in a manner that correlated with CD38 enzymatic activity. The plasma cell-specific binding of VLRB MM3 contrasts with the broad pattern of expression of CD38-determined conventional antibodies specific for this antigen. In an effort to facilitate the application of this unique reagent in combination with conventional antibody panels, we explored a strategy to generate VLRB MM3 tetramers. The resulting reagent maintained the threshold-based recognition of CD38. Increased sensitivity achieved with VLRB MM3 tetramers also showed preferential recognition of germinal center centroblasts over centrocytes. VLRB MM3 tetramers thus provided a unique and versatile single-step staining reagent for the detection of human CD38 that is readily incorporated into multi-color flow cytometry panels.

We identify a cell type–specific modification of HLA-I using lamprey VLR antibodies as a new class of research reagents., Memory B cells and plasma cells are antigen-experienced cells tasked with the maintenance of humoral protection. Despite these prominent functions, definitive cell surface markers have not been identified for these cells. We report here the isolation and characterization of the monoclonal variable lymphocyte receptor B (VLRB) N8 antibody from the evolutionarily distant sea lamprey that specifically recognizes memory B cells and plasma cells in humans. Unexpectedly, we determined that VLRB N8 recognizes the human leukocyte antigen–I (HLA-I) antigen in a tyrosine sulfation–dependent manner. Furthermore, we observed increased binding of VLRB N8 to memory B cells in individuals with autoimmune disorders multiple sclerosis and systemic lupus erythematosus. Our study indicates that lamprey VLR antibodies uniquely recognize a memory B cell– and plasma cell–specific posttranslational modification of HLA-I, the expression of which is up-regulated during B cell activation.

FCRL4, a low-affinity IgA Ab receptor with strong immunoregulatory potential, is an identifying feature of a tissue-based population of memory B cells (Bmem). We used two independent approaches to perform a comparative analysis of the Ag receptor repertoires of FCRL4+ and FCRL4− Bmem in human tonsils. We determined that FCRL4+ Bmem displayed lower levels of somatic mutations in their Ag receptors compared with FCRL4− Bmem but had similar frequencies of variable gene family usage. Importantly, Abs with reactivity to commensal microbiota were enriched in FCRL4+ cells, a phenotype not due to polyreactive binding characteristics. Our study links expression of the immunoregulatory FCRL4 molecule with increased recognition of commensal microbial Ags.

The antigen-presenting cell–expressed CD40 is implied in the regulation of counteractive immune responses such as induction of pro-inflammatory and anti-inflammatory cytokines interleukin (IL)–12 and IL-10, respectively. The mechanism of this duality in CD40 function remains unknown. Here, we investigated whether such duality depends on ligand binding. Based on CD40 binding, we identifed two dodecameric peptides, peptide-7 and peptide-19, from the phage peptide library. Peptide-7 induces IL-10 and increases Leishmania donovani infection in macrophages, whereas peptide-19 induces IL-12 and reduces L. donovani infection. CD40-peptide interaction analyses by surface plasmon resonance and atomic force microscopy suggest that the functional differences are not associated with the studied interaction parameters. The molecular dynamic simulation of the CD40-peptides interaction suggests that these two peptides bind to two different places on CD40. Thus, we suggest for the first time that differential binding of the ligands imparts functional duality to CD40.

The interactions between the protozoan parasite Leishmania and host macrophages are complex and involve several paradoxical functions that are meant for protection of the host but exploited by the parasite for its survival. The initial interaction of the parasite surface molecules with the host-cell receptors plays a major role in the final outcome of the disease state. While the interactions between macrophages and a virulent strain of Leishmania trigger a cascade of cell-signaling events leading to immunosuppression, the interaction with an avirulent strain triggers host-protective immune effector functions. Thus, an incisive study on Leishmania–macrophage interactions reveals functional paradoxes that highlight the concept of ‘relativity in parasite virulence’. Using Leishmania infection as a model, we propose that virulence of a pathogen and the resistance (or susceptibility) of a host to the pathogen are relative properties that equate to combinatorial functions of several sets of molecular processes.

The process of developing drugs dates to antiquity. The herbal formulations during the old days were more traditional than with any scientific rationale. As different branches of physics, chemistry and biology started revealing the physiological processes in molecular details and as the sophisticated methods for probing into these phenomena were innovated, the processes of drug development changed significantly. However, the very first step in the process which is defining a drug target remains a major hurdle. The classical methods that predate the functional genomics and proteomics involve a cumbersome, painstaking detailing of a given enzyme or a receptor, followed by its validation as a target. The sophisticated methods in the post-genomic and proteomic era reduced the time taken to define targets, but the speed of drug discovery is not necessarily as quick as it promised. This is primarily due to prolific predictions pressing validation too hard, although both non-robotic and robotic high throughput screenings match with the requirement. Since these drugs target pathogens, a serious disadvantage with these methodologies is the emergence of drug resistance. Therefore, we propose a functional approach whereby the host-pathogen interaction is studied to find out the alterations in immune responses, the profile of host gene expression and activation of cell signaling molecules, the kinases in particular. Such interactions often induce the expression of those genes and activation of those proteins which are required for their survival. We demonstrate that reversal of such profiles of gene expression and protein activation ameliorates the infection. Therefore, those gene products and the kinases with pro-parasitic functions can serve as targets.

Uma Sinha-Datta, Srijit Khan, Dhananjay WadgaonkarFast Trak, GE Healthcare Life Science, John F Welch Technology Centre, Bangalore, IndiaAbstract: In the biosimilar eon, where various analytical platforms are needed to show biosimilarity, we demonstrate the use of surface plasmon resonance biosensor as a label-free interaction analysis tool to compare two therapeutic monoclonal antibodies (mAb1-i and mAb2-i) with their biosimilars (mAb1-B and mAb2-B1, B2, B3) based on kinetics, affinity, and thermal stability studies. We calculate active analyte concentration using Biacore systems' calibration-free concentration analysis method and demonstrate its importance for kinetic evaluation. The kinetic constants (ka and kd) and affinity constant (KD) of the mAbs for binding to specific antigens were evaluated. It was found that the biosimilars were very similar to their innovator with respect to binding to its antigen demonstrating functional similarity. To further confirm biosimilarity to the originator molecules, we conducted a thermal stability analysis of both mAbs using differential scanning calorimetry. This analysis showed good structural similarity in between innovator antibodies and biosimilars, with major Tm as 84.1°C (mAb1) and 72.8°C (mAb2), demonstrating structural similarity.Keywords: surface plasmon resonance, Biacore, kinetics, low level of ligand immobilization, calibration-free concentration analysis, bivalent analytes, active concentration

Reference EPFL-ARTICLE-184154doi:10.1016/j.humimm.2012.07.001View record in Web of Science Record created on 2013-02-27, modified on 2017-05-12