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An assessment of the factors contributing to the killing of type 3 Streptococcus pneumoniae by human polymorphonuclear leukocytes in vitro
Author(s) -
Esposito ANTHONY L.,
Clark CAROLYN A.,
Poirier WILLIAM J.
Publication year - 1990
Publication title -
apmis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.909
H-Index - 88
eISSN - 1600-0463
pISSN - 0903-4641
DOI - 10.1111/j.1699-0463.1990.tb01009.x
Subject(s) - antibody opsonization , phagocytosis , microbiology and biotechnology , streptococcus pneumoniae , degranulation , bacteria , in vitro , superoxide , leukotriene b4 , lactoferrin , biology , lysis , opsonin , chemistry , immunology , enzyme , antibiotics , inflammation , biochemistry , receptor , genetics
To characterize the factors that contribute to the killing of type 3 S. pneumoniae , human neutrophils were obtained from healthy donors and incubated with viable organisms. In contrast to prior observations with other pneumococcal serotypes, killing was not detected when 10 6 colony forming units (cfu) were incubated at 37°C for 2–4 hours with 10 6 neutrophils in the presence of 20–80% fresh autologous serum; further, pneumococcidal activity was not found when preopsonized bacteria and primed neutrophils were employed in the standard assay. However, when the bacterium to cell ratio was reduced to 1:100 and 1:1000, microbicidal action was detected; a 10‐fold reduction in the number of viable bacteria was observed when 2 times 10 3 cfu were incubated with 2 times 10 6 neutrophils and 80% autologous serum at 37°C for 4 hours. To assess the effects of serum factors on killing, bactericidal assays were performed in the presence of normal human serum (NHS), heat‐inactivated human serum (HIHS) and absorbed human serum (AHS); heating reduced and absorption eliminated the capacity of serum to support killing. Studies performed with mutanolysin, an enzyme that lyses type 3 pneumococci, demonstrated that the effects of HIHS and AHS on bactericidal activity were highly correlated with alterations in the ability of the sera to support phagocytosis. Studies of neutrophil activation revealed changes in the production of superoxide anion that correlated well with phagocytosis and killing; however, the results of assays of leukotriene B 4 generation and degranulation (beta‐glucuronidase and lactoferrin release) were more variable. In mixing experiments, the capacity of HIHS to support killing was normalized with NHS; however, the ability of AHS to promote killing was not restored with HIHS or NHS. Thus, these studies demonstrate the relatively limited capacity of human serum to support the killing of type 3 pneumococci, and they emphasize the importance of killing assays in assessing interactions between the bacterium and neutrophils.