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Structural characterization of GASDALIE Fc bound to the activating Fc receptor Fc?RIIIa.

ABSTRACT: The Fc region of Immunoglobulin G (IgG) initiates inflammatory responses such as antibody-dependent cell-mediated cytotoxicity (ADCC) through binding to activating Fc receptors (Fc?RI, Fc?RIIa, Fc?RIIIa). These receptors are expressed on the surface of immune cells including macrophages, dendritic cells, and natural killer cells. An inhibitory receptor, Fc?RIIb, is expressed on macrophages and other myeloid leukocytes simultaneously with the activating receptor Fc?RIIa, thereby setting a threshold for cell activation. The affinity of IgG Fc for binding activating Fc receptors depends on IgG subclass and the composition of N-linked glycans attached to a conserved asparagine in the Fc CH2 domain. For example, Fc regions with afucosylated glycans bind more tightly to Fc?RIIIa than fucosylated Fc, and afucosylated Fcs exhibit enhanced ADCC activity in vivo and in vitro. Enhanced pro-inflammatory responses have also been seen for Fc regions with amino acid substitutions. GASDALIE Fc is an Fc mutant (G236A/S239D/A330L/I332E) that exhibits a higher affinity for Fc?RIIIa and increased effector functions in vivo compared to wild-type Fc. To explore its altered functions, we compared the affinities of GASDALIE and wild-type Fc for activating and inhibitory Fc?Rs. We also determined the crystal structure of GASDALIE Fc alone and bound to Fc?RIIIa. The overall structure of GASDALIE Fc alone was similar to wild-type Fc structures, however, increased electrostatic interactions in the GASDALIE Fc:Fc?RIIIa interface compared with other Fc:Fc?R structures suggest a mechanism for the increased affinity of GASDALIE Fc for Fc?RIIIa.

SUBMITTER: Ahmed AA

PROVIDER: S-EPMC4769027 | biostudies-literature | 2016 Apr

REPOSITORIES: biostudies-literature

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Structural characterization of GASDALIE Fc bound to the activating Fc receptor FcγRIIIa.

Ahmed Alysia A AA Keremane Sravya R SR Vielmetter Jost J Bjorkman Pamela J PJ

Journal of structural biology 20160202 1

The Fc region of Immunoglobulin G (IgG) initiates inflammatory responses such as antibody-dependent cell-mediated cytotoxicity (ADCC) through binding to activating Fc receptors (FcγRI, FcγRIIa, FcγRIIIa). These receptors are expressed on the surface of immune cells including macrophages, dendritic cells, and natural killer cells. An inhibitory receptor, FcγRIIb, is expressed on macrophages and other myeloid leukocytes simultaneously with the activating receptor FcγRIIa, thereby setting a thresho ...[more]

PMID: 26850169

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Project description:Chronic HIV-infection modulates the expression of Fc gamma receptors (Fc?Rs) on immune cells and their antibody-dependent effector function capability. Given the increasingly recognized importance of antibody-dependent cellular cytotoxicity (ADCC) in HIV-specific immunity, we investigated the cellular distribution of Fc?RIIIa on cytotoxic lymphocytes-natural killer cells and CD8+ T cells-and the effect of the Fc?RIIIa-F158V variant on ADCC capacity in HIV-infected individuals (n = 23) and healthy controls (n = 23). Study participants were matched for F158V genotypes, carried two copies of the FCGR3A gene and were negative for Fc?RIIb expression on NK cells. The distribution of CD56dimFc?RIIIabright and CD56negFc?RIIIabright NK cell subsets, but not Fc?RIIIa surface expression, differed significantly between HIV-1 negative and HIV-1 positive donors. NK cell-mediated ADCC responses negatively correlated with the proportion of the immunoregulatory CD56brightFc?RIIIadim/neg cells and were lower in the HIV-1 positive group. Intriguingly, the Fc?RIIIa-F158V variant differentially affected the NK-mediated ADCC responses for HIV-1 negative and HIV-1 positive donors. Healthy donors bearing at least one 158V allele had higher ADCC responses compared to those homozygous for the 158F allele (48.1 vs. 34.1%), whereas the opposite was observed for the HIV-infected group (26.4 vs. 34.6%), although not statistically significantly different. Furthermore, Fc?RIIIa+CD8bright and Fc?RIIIa+CD8dim T cell subsets were observed in both HIV-1 negative and HIV-1 positive donors, with median proportions that were significantly higher in HIV-1 positive donors compared to healthy controls (15.7 vs. 8.3%; P = 0.016 and 18.2 vs. 14.1%; P = 0.038, respectively). Using an HIV-1-specific GranToxiLux assay, we demonstrate that CD8+ T cells mediate ADCC through the delivery of granzyme B, which was overall lower compared to that of autologous NK cells. In conclusion, our findings demonstrate that in the presence of an HIV-1 infection, the cellular distribution of Fc?RIIIa is altered and that the functional consequence of Fc?RIIIa variant is affected. Importantly, it underscores the need to characterize Fc?R expression, cellular distribution and functional consequences of Fc?R genetic variants within a specific environment or disease state.

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Dataset Information

Structural characterization of GASDALIE Fc bound to the activating Fc receptor Fc?RIIIa.

Publications

Structural characterization of GASDALIE Fc bound to the activating Fc receptor FcγRIIIa.

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