PubMed · 3912627
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J Egido de los Ríos. 1985-11-30. [IgA nephropathy].. https://pubmed.ncbi.nlm.nih.gov/3912627/
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We investigated the interaction of immune complexes (IC) isolated from hepatitis C virus (HCV)-infected individuals with several cell lines that differentially express Fc receptors, and analyzed viral infection by the presence of HCV RNA sequences. Monocytic (U937 and Monomac-6) and lymphocytic (MOLT-4 and Jurkat) cell lines were incubated with interferon- plus phorbol myristate acetate to stimulate the expression of Fc receptors before addition of IC. Cell interaction with IC was monitored by flow cytometry. Positive cell fluorescence was detected in U937 and Monomac-6 cells [mean fluorescence intensity (MFI) 10.56+/-0.8 and 11.60+/-0.8, respectively]. Incubation of cells with monoclonal antibodies against Fc receptors for IgG before addition of IC decreased MFI in both cell lines (U937 2.1+/-0.5, Monomac-6 4.4+/-0.8, P<0.001), indicating that cell-IC interaction through these receptors was inhibited. In particular, the blockage of FcgammaRII was responsible for this effect. No binding of IC with either MOLT-4 or Jurkat cell lines was detected, which correlated with a very low Fc receptor expression. HCV RNA sequences were identified in the cells up to 120 h of post incubation with IC. These results suggest that IC can mediate entry of HCV to both U-937 and Monomac-6 cell lines mainly through the FcgammaRII.
The NNA7 Fab fragment recognizes the human glycopeptide N blood-group antigen and has a high affinity for N-type glycophorin A (GPA). To provide insight into how antibodies recognize glycopeptide antigens, soluble Fab fragments were expressed in Escherichia coli, purified and crystallized using the hanging-drop vapor-diffusion method at 293 K. The best crystals were obtained from solutions of PEG monomethyl ether 5000 containing 4-8 mM yttrium chloride (YCl3). This rare-earth ion, which could be substituted with various lanthanides, changed the habit of crystals from multinucleated rods with a diffraction limit of 4.25 A resolution to a diamond-shaped morphology that grew as single crystals and diffracted X-rays to 1.75 A resolution. Data were collected that indicated that the crystals belonged to space group P2(1)2(1)2(1), with unit-cell parameters a = 57.9, b = 77.1, c = 118.1 A and one Fab fragment per asymmetric unit. A molecular-replacement solution has been obtained and 86% of the molecule was fitted by use of an automated refinement procedure (ARP).
BACKGROUND: The CD32 (FcgammaII) receptor is involved in the regulation of the B cell response to antigen. The sole Fc receptor demonstrated in mice is the inhibitory FcgammaIIB receptor. Crosslinking this receptor does not lead to downstream signaling or cell activation. Instead, when immune complexes bind to Fcy on murine B cells, cell activation through the B cell antigen receptor is attenuated. The objective of this study was to evaluate the expression of the FcgammaII receptor and the response to immune complex stimulation in human B cells. METHODS: Human lymphoblastoid, peripheral and tonsillar B cells were stained with anti-CD32 antibodies IV.3 and 8.26 to determine the relative expression of the activating (FcgammaIIA) and inhibitory (FcgammaIIB) isoforms of CD32. Tetanus immune complexes were added to B cells and the activation of c-Jun amino-terminal kinase was assayed. RESULTS: Unlike murine cells, human B cells express high levels of the activating form of the Fcgamma receptor IIA. Addition of immune complexes to peripheral B cells resulted in signaling of Jun kinase, an important downstream kinase involved in the regulation of B cell function. The level of expression of FcgammaIIA on human B cells was not uniform, but depended on activation status. Peripheral blood B cells expressed high levels of FcgammaIIA, while tonsillar B cells predominantly expressed FcgammaIIB. Furthermore, when peripheral B cells were activated, the expression of FcgammaIIA relative to FcgammaIIB decreased. CONCLUSION: The response of human B cells to binding of immune complexes depends on the relative expression of activating (FcgammaIIA) versus inhibitory (FcgammaIIB) receptors.