THE ANTI-LIPID-A MONOCLONAL-ANTIBODY E5 BINDS TO ROUGH GRAM-NEGATIVE BACTERIA, FIXES C3, AND FACILITATES BINDING OF BACTERIAL IMMUNE-COMPLEXES TO BOTH ERYTHROCYTES AND MONOCYTES
Ma. Seelen et al., THE ANTI-LIPID-A MONOCLONAL-ANTIBODY E5 BINDS TO ROUGH GRAM-NEGATIVE BACTERIA, FIXES C3, AND FACILITATES BINDING OF BACTERIAL IMMUNE-COMPLEXES TO BOTH ERYTHROCYTES AND MONOCYTES, Immunology, 84(4), 1995, pp. 653-661
Treatment of patients with septic shock using monoclonal antibodies (m
Abs) to endotoxin is still controversial. Clinical trials of E5, one o
f the mAbs directed against the lipid A moiety of lipopolysaccharide (
LPS), are currently in progress, The mechanisms of action of this, and
other antibodies under clinical evaluation, are, however, poorly unde
rstood. In this study we examined in vitro the ways in which E5 intera
cted with Gram-negative bacteria, complement, erythrocytes and monocyt
es. By fluorescence-activated cell sorter (FAGS) analysis we showed di
rect, dose-dependent binding of E5 to Escherichia coli (E. coli) and S
almonella minnesota (S. minnesota). Antibody binding to S. minnesota w
as enhanced by treatment with the p-lactam antibiotic amoxycillin, but
not by treatment with the aminoglycoside gentamicin. Immune complexes
formed between E5 and both species of Gram-negative bacteria activate
d both classical and alternative complement pathways, but only in the
case of S. minnesota did this facilitate binding to erythrocyte CR1 an
d monocyte CR3. Bacterial C3b and iC3b fixation by E5 was quantified u
sing specific mAbs. These observations suggest that E5 may enhance bac
terial clearance in several ways: (1) by facilitating direct complemen
t fixation; (2) by facilitating the binding of opsonized bacteria to c
ells of the mononuclear phagocyte system; (3) by enabling bacteria to
bind to erythrocyte CRI (CD35), allowing safe carriage in the circulat
ion to the fixed macrophages of the liver and spleen; (4) by acting sy
nergistically with beta-lactam antibiotics.