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Infect. Immun., Jul 1996, 2425-2430, Vol 64, No. 7
LM Madsen, M Inada and J Weiss
Prompt killing of many strains of Escherichia coli during phagocytosis in
vitro by isolated polymorphonuclear leukocytes (PMN) requires the presence
of nonlethal doses of nonimmune serum (B. A. Mannion, J. Weiss, and P.
Elsbach, J. Clin. Invest. 86:631-641, 1990). Because this requirement is
bypassed in a phospholipase A (PLA)-rich mutant (pldA ) of E. coli, we have
examined the effect of serum on bacteria] phospholipid (PL) degradation
during phagocytosis of wild-type (pldA+) and PLA-deficient (pldA) E. coli.
In parallel with increased killing, nonlethal doses of serum increased the
degradation of prelabeled bacterial PL during phagocytosis by two- to
fivefold, to nearly the same levels (ca. 50 to 60%) as those produced
during phagocytosis of E. coli pldA in the absence of serum. The effects on
the E. coli pldA mutant imply that there is a serum-mediated enhancement of
granule- associated group II PMN PLA2 activity. At the same doses, serum
promoted action against E. coli in the presence of purified rabbit and
human group II PLA2 but did not activate bacterial PLA. Related PLA2s that
lack specific structural determinants needed for optimal activity against
E. coli treated with the bactericidal/permeability-increasing protein (BPI)
of PMN are also less active than wild-type group II PLA2 against
serum-treated E. coli. Treatment of E. coli with C7- or C9- depleted serum
did not enhance bacterial killing or PL degradation during phagocytosis or
the action of purified PLA2. In summary, these findings suggest that (i)
nonlethal assemblies of the membrane attack complex promote intracellular
killing and destruction of E. coli ingested by PMN, in part by promoting
the action of granule-associated PLA2 against ingested bacteria, and (ii)
structural determinants first implicated in PLA2 action against BPI-treated
E. coli are also important in PLA2 action in concert with other host
defense systems, such as complement.
Copyright © 1996, American Society for Microbiology
Determinants of activation by complement of group II phospholipase A2 acting against Escherichia coli
Department of Microbiology, New York University School of Medicine, New York 10016, USA.
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