Dependence of immunoglobulin class switch recombination in B Cells on vesicular release of ATP and CD73 ectonucleotidase activity

Immunoglobulin (Ig) isotype diversification by class switch recombination (CSR) is an essential process for mounting a protective humoral immune response. Ig CSR deficiencies in humans can result from an intrinsic B cell defect; however, most of these deficiencies are still molecularly undefined and diagnosed as common variable immunodeficiency (CVID). Here, we show that extracellular adenosine critically contributes to CSR in human naive and IgM memory B cells. In these cells, coordinate stimulation of B cell receptor and toll-like receptors results in the release of ATP stored in Ca2+-sensitive secretory vesicles. Plasma membrane ectonucleoside triphosphate diphosphohydrolase 1 CD39 and ecto-5′-nucleotidase CD73 hydrolyze ATP to adenosine, which induces CSR in B cells in an autonomous fashion. Notably, CVID patients with impaired class-switched antibody responses are selectively deficient in CD73 expression in B cells, suggesting that CD73-dependent adenosine generation contributes to the pathogenesis of this disease

A hemolytic peptide from the mycophilic fungus Sepedonium chrysospermum (Bull.) Fr.

none6SANGUINETI E; COSULICH E; SALIS A; DAMONTE G; M. MARIOTTI; ZOTTI MSanguineti, Elisa; Cosulich, E; Salis, Annalisa; Damonte, Gianluca; Mariotti, Mauro; Zotti, Mirc

Susceptibility ofVibrio Aestuarianus01/032 to the Antibacterial Activity ofMytilusHemolymph: Identification of A Serum Opsonin Involved in Mannose-Sensitive Interactions

The interactions of Vibrio aestuarianus 01/032 with hemolymph of the bivalves Mytilus galloprovincialis and Crassostrea gigas were investigated to understand if hemolymph components (hemocytes and soluble factors) could be involved in the higher resistance to microbial infection shown by mussels in comparison to oysters. Although 01/032 bacteria adhered to hemocytes of both bivalves, they were sensitive to the bactericidal activity of whole hemolymph from mussel but not from oyster; in addition, adhesion to mussel (but not oyster) hemocytes was affected by D-mannose. Mussel serum opsonins directed towards D-mannose - binding bacterial ligands were purified by affinity chromatography and were shown to mediate 01/032 interactions with M. galloprovincialis hemocytes. Nano-HPLC-ESI-MS/MS analysis showed that the purified opsonin matched to the protein precursor of the extrapallial protein (EP) [Mytilus edulis]. In the presence of M. galloprovincialis EP protein (MgEP), C. gigas hemocytes killed V. aestuarianus 01/032 almost as efficiently as mussel phagocytes. These findings suggest that the different sensitivity of 01/032 strain to the antibacterial activity of oyster and mussel hemolymph might partly depend on the fact that C. gigas serum lacks MgEP-like opsonins. These results represent the basis for understanding the different sensitivity to microbial infections shown by the two bivalve species

Susceptibility of Vibrio aestuarianus 01/032 to the antibacterial activity of Mytilus haemolymph: Identification of a serum opsonin involved in mannose-sensitive interactions

The interactions of Vibrio aestuarianus 01/032 with haemolymph of the bivalves Mytilus galloprovincialis and Crassostrea gigas were investigated to understand if haemolymph components (haemocytes and soluble factors) could be involved in the higher resistance to microbial infection shown by mussels in comparison with oysters. Although 01/032 bacteria adhered to haemocytes of both bivalves, they were sensitive to the bactericidal activity of whole haemolymph from mussel, but not from oyster; in addition, adhesion to mussel (but not oyster) haemocytes was affected by D-mannose. Mussel serum opsonins directed towards D-mannose-binding bacterial ligands were purified by affinity chromatography and were shown to mediate 01/032 interactions with M.galloprovincialis haemocytes. Nano-High Performance Liquid Chromatography-Electrospray Ionization-Tandem Mass Spectrometry (HPLC-ESI-MS/MS) analysis showed that the purified opsonin matched the protein precursor of Mytilus edulis extrapallial protein (EP). In the presence of M.galloprovincialisEP protein (MgEP), C.gigas haemocytes killed V.aestuarianus 01/032 almost as efficiently as mussel phagocytes. These findings suggest that the different sensitivity of 01/032 strain to the antibacterial activity of oyster and mussel haemolymph might partly depend on the fact that C.gigas serum lacks MgEP-like opsonins. These results represent the basis for understanding the different sensitivity to microbial infections shown by the two bivalve species

Dependence of Immunoglobulin Class Switch Recombination in B Cells on Vesicular Release of ATP and CD73 Ectonucleotidase Activity

Immunoglobulin (Ig) isotype diversification by class switch recombination (CSR) is an essential process for mounting a protective humoral immune response. Ig CSR deficiencies in humans can result from an intrinsic B cell defect; however, most of these deficiencies are still molecularly undefined and diagnosed as common variable immunodeficiency (CVID). Here, we show that extracellular adenosine critically contributes to CSR in human naive and IgM memory B cells. In these cells, coordinate stimulation of B cell receptor and toll-like receptors results in the release of ATP stored in Ca2+-sensitive secretory vesicles. Plasma membrane ectonucleoside triphosphate diphosphohydrolase 1 CD39 and ecto-5′-nucleotidase CD73 hydrolyze ATP to adenosine, which induces CSR in B cells in an autonomous fashion. Notably, CVID patients with impaired class-switched antibody responses are selectively deficient in CD73 expression in B cells, suggesting that CD73-dependent adenosine generation contributes to the pathogenesis of this disease

Dysregulation in B-cell responses and T follicular helper cell function in ADA2 deficiency patients

Adenosine deaminase 2 deficiency (DADA2) is an autoinflammatory disease characterized by inflammatory vasculopathy, early strokes associated often with hypogammaglobulinemia. Pure red cell aplasia, thrombocytopenia, and neutropenia have been reported. The defect is due to biallelic loss of function of ADA2 gene, coding for a protein known to regulate the catabolism of extracellular adenosine. We therefore investigated immune phenotype and B- and T-cell responses in 14 DADA2 patients to address if ADA2 mutation affects B- and T-cell function. Here, we show a significant decrease in memory B cells, in particular class switch memory, and an expansion of CD21low B cells in DADA2 patients. In vitro stimulated B lymphocytes were able to secrete nonfunctional ADA2 protein, suggesting a cell intrinsic defect resulting in an impairment of B-cell proliferation and differentiation. Moreover, CD4+ and CD8+ T cells were diminished; however, the frequency of circulating T follicular helper cells was significantly increased but they had an impairment in IL-21 production possibly contributing to an impaired B cell help. Our findings suggest that ADA2 mutation could lead to a B-cell intrinsic defect but also to a defective Tfh cell function, which could contribute to the immunodeficient phenotype reported in DADA2 patients