title: Non-opsonic phagocytosis of homologous non-toxigenic and toxigenic Corynebacterium diphtheriae strains by human U-937 macrophages.
abstract: As interactions between bacteria and macrophages dictate the outcome of most infectious diseases, analyses of molecular mechanisms of non-opsonic phagocytosis should lead to new approaches for the prevention of diphtheria and systemic Corynebacterium diphtheriae infections. The present study aimed to evaluate human macrophage-bacteria interactions in the absence of opsonin antibodies and the influence of the tox gene on this process. Homologous C. diphtheriae tox+ and tox- strains were evaluated for adhesion, entering and survival within U-937 human macrophages at different incubation periods. Higher numbers of viable bacteria associated with and internalized by macrophages were demonstrated for the tox+ strain. However, viable intracellular bacteria were detected at T-24 hr only for the tox- strain. Cytoskeletal inhibitors, cytochalasin E, genistein and colchicine, inhibited intracellular viability of both strains at different levels. Bacterial replication was evidenced at T-24 hr in supernatants of monolayers infected with the tox- strain. Host cell death and nuclear alterations were evidenced by the Trypan blue exclusion assay and DAPI fluorescence microscopy. ELISA of histone-associated DNA fragments allowed detection of apoptosis and necrosis induced by tox+ and tox- strains at T-1 hr and T-3 hr. In conclusion, human macrophages in the absence of opsonins may not be promptly effective at killing diphtheria bacilli. The presence of the tox gene influences the susceptibility of C. diphtheriae to human macrophages and the outcome of non-opsonic phagocytosis. C. diphtheriae strains exhibit strategies to survive within macrophages and to exert apoptosis and necrosis in human phagocytic cells, independent of the tox gene.
authors.affiliation: Institute of Microbiology Professor Paulo de Góes, Federal University of Rio de Janeiro, Centro de Ciências da Saúde, Bloco I, Cidade Universitária-Ilha do Fundão, Rio de Janeiro, Brazil.
authors.forename: Cíntia Silva
authors.initials: CS
authors.lastname: dos Santos
authors.forename: Louisy Sanches
authors.initials: LS
authors.lastname: dos Santos
authors.forename: Monica Cristina
authors.initials: MC
authors.lastname: de Souza
authors.forename: Fernanda
authors.initials: F
authors.lastname: dos Santos Dourado
authors.forename: Alexandre Alves
authors.initials: AA
authors.lastname: de Souza de Oliveira Dias
authors.forename: Priscila Soares
authors.initials: PS
authors.lastname: Sabbadini
authors.forename: Gabriela Andrade
authors.initials: GA
authors.lastname: Pereira
authors.forename: Maulori Curié
authors.initials: MC
authors.lastname: Cabral
authors.forename: Raphael
authors.initials: R
authors.lastname: Hirata Junior
authors.forename: Ana Luíza
authors.initials: AL
authors.lastname: de Mattos-Guaraldi
mesh_terms: D020533:Angiogenesis Inhibitors / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D001422:Bacterial Adhesion / Q000235:genetics / Q000502:physiology; D003078:Colchicine / Q000494:pharmacology; D003353:Corynebacterium diphtheriae / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D003572:Cytochalasins / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay; D019833:Genistein / Q000494:pharmacology; D006801:Humans; D008264:Macrophages / Q000166:cytology / Q000187:drug effects / Q000378:metabolism* / Q000382:microbiology*; D008856:Microscopy, Fluorescence; D009336:Necrosis / Q000139:chemically induced; D010587:Phagocytosis / Q000235:genetics / Q000502:physiology*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D050257:Tubulin Modulators / Q000494:pharmacology; D020298:U937 Cells
chemical_list: D020533:Angiogenesis Inhibitors; D003572:Cytochalasins; D047428:Protein Kinase Inhibitors; D050257:Tubulin Modulators; C007215:cytochalasin E; D019833:Genistein; D003078:Colchicine