Lectin‐Mediated, Nonopsonic Phagocytosis of Type 1 Escherichia coli by Human Peritoneal Macrophages of Uremic Patients Treated by Peritoneal Dialysis

Human peritoneal macrophages isolated from uremic patients undergoing peritoneal dialysis bind type 1 fimbriated Escherichia coli in the absence of opsonins. The number of bacteria bound per macrophage was 6.9, as determined by microscopic examination. Methyl α‐mannoside (0.1 mM) and p ‐nitrophenyl α‐mannoside (0.01 mM) inhibited this binding by about 66%. The ability of peritoneal macrophages to bind E . coli in a mannose‐specific manner was confirmed in further experiments using an enzyme‐linked immunosorbent assay (ELISA) with an antibacterial antibody, radiolabelled E. coli , and counts of colony‐forming units (CFU). The number of bacteria bound per macrophage was 7 to 12 in the ELISA and 5.5‐8.5 in the CFU assay. Methyl α‐mannoside caused 70% inhibition of binding In the ELISA and 84% in the CFU assay, whereas p ‐nitrophenyl α‐mannoside showed inhibition of 79% and 90%, respectively. Most bound bacteria (76‐80%) were subsequently killed. Nonfimbriated E . coli 827 bound poorly to the macrophages (~22%) as compared to that of the fimbriated bacteria. Although this binding was not inhibited by methyl α‐D‐mannoside or p ‐nitrophenyl α‐mannoside, the percentage of bacteria killed was similar to that of the fimbriated phenotype. The peritoneal macrophage is thus able to phagocytose E . coli in the absence of opsonins. This may explain the relative rarity of E . coli as an etiologic agent of peritoneal infections in the dialysed patient.