Biomedical subjects

R Alan B Ezekowitz

Publications and source records attributed to R Alan B Ezekowitz.

22 records · Page 2Linked to original sources

PubMed2003

Identification of cytoskeletal regulatory proteins required for efficient phagocytosis in Drosophila.

Phagocytosis is a complex and apparently evolutionarily conserved process that plays a central role in the immune response to infection. By ultrastructural and functional criteria, Drosophila hemocyte (macrophage) phagocytosis resembles mammalian phagocytosis. Using a non-saturated forward genetic screen for larval hemocyte phagocytosis mutants, D-SCAR and profilin were identified as important regulators of phagocytosis in Drosophila. In both hemocytes ex vivo and the macrophage-like S2 cell line, lack of D-SCAR significantly decreased phagocytosis of Escherichia coli and Staphylococcus aureus. In contrast, profilin mutant hemocytes exhibited increased phagocytic activity. Analysis of double mutants suggests that D-SCAR and profilin interact during phagocytosis. Finally, RNA interference studies in S2 cells indicated that the D-SCAR homolog D-WASp also participates in phagocytosis. This study demonstrates that Drosophila provides a viable model system in which to dissect the complex interactions that regulate phagocytosis.

Actin Cytoskeleton↗

PubMed2002

Functional genomic analysis of phagocytosis and identification of a Drosophila receptor for E. coli.

The recognition and phagocytosis of microbes by macrophages is a principal aspect of innate immunity that is conserved from insects to humans. Drosophila melanogaster has circulating macrophages that phagocytose microbes similarly to mammalian macrophages, suggesting that insect macrophages can be used as a model to study cell-mediated innate immunity. We devised a double-stranded RNA interference-based screen in macrophage-like Drosophila S2 cells, and have defined 34 gene products involved in phagocytosis. These include proteins that participate in haemocyte development, vesicle transport, actin cytoskeleton regulation and a cell surface receptor. This receptor, Peptidoglycan recognition protein LC (PGRP-LC), is involved in phagocytosis of Gram-negative but not Gram-positive bacteria. Drosophila humoral immunity also distinguishes between Gram-negative and Gram-positive bacteria through the Imd and Toll pathways, respectively; however, a receptor for the Imd pathway has not been identified. Here we show that PGRP-LC is important for antibacterial peptide synthesis induced by Escherichia coli both in vitro and in vivo. Furthermore, totem mutants, which fail to express PGRP-LC, are susceptible to Gram-negative (E. coli), but not Gram-positive, bacterial infection. Our results demonstrate that PGRP-LC is an essential component for recognition and signalling of Gram-negative bacteria. Furthermore, this functional genomic approach is likely to have applications beyond phagocytosis.

Actins↗

PubMed2002

The complement response against an oncolytic virus is species-specific in its activation pathways.

A variety of oncolytic viruses (OVs) are being tested in clinical trials for different human cancers. Although the innate immune response is critical as the first line of defense in thwarting viral infection of mammalian cells, little is known of this response in the context of OV therapy of tumors. Investigations of activities against a herpes simplex OV demonstrated that HSV-seronegative sera from rats, mice, and humans efficiently neutralize this OV in vitro. Although this neutralization is due to complement, activation of this innate host defense differs in its pathways among species routinely used in preclinical tumor trials. In rats, both natural immunoglobulins and mannan-binding lectin (MBL) activate complement against the OV, while in mice only MBL is relevant to this activation. However, in humans only natural immunoglobulins play a role in complement activity. Quantitative analyses confirm that in vivo complement depletion facilitates the initial infection of tumors by systemic OVs. Therefore, complement activation against oncolytic HSV vectors proceeds through different pathways in different species. These findings are relevant to preclinical rodent studies of OV therapy and their application to human clinical trials.

Animals↗

PubMed2002

Lack of mannose-binding lectin-A enhances survival in a mouse model of acute septic peritonitis.

The mannose-binding lectin (MBL) (also known as the mannose-binding protein) is a serum protein that plays a role as an "ante-antibody" in innate immunity. In man, MBL is encoded by a single gene, whereas in mice there are two homologous proteins, MBL-A and MBL-C. In order to evaluate the relative roles of these two forms of MBL, we created MBL-A null mice that were MBL-C sufficient. We found MBL-A null mice had enhanced survival in a septic peritonitis model compared to wild-type mice and complement 3 null mice at 24 h, 48 h and 10 d (P < 0.05). Reconstitution of these mice with human MBL reversed the phenotype. Surviving mice had significantly decreased TNF-alpha and IL-6 levels in the blood and peritoneal cavity (P < 0.01). In vitro studies indicate that bacteria opsonized with MBL-A-deficient serum induced significantly less cytokine by peritoneal macrophages compared to those with wild-type serum. Our results indicate that MBL-A is a modulator of inflammation in vivo and in vitro in the mouse and that the role of MBL may extend beyond its role as an opsonin.

Animals↗