Pneumococcal immune adherence to human erythrocytes.
BACKGROUND
Human red blood cells bind various C3b-coated microorganisms via their C3b/CR1 receptor, a phenomenon referred to as immune adherence. The aim of the present study was to measure pneumococcal adherence to human red blood cells by flow cytometry and to study kinetic aspects of this binding.


METHODS
We quantified pneumococcal adherence to human erythrocytes by FACS analysis and tested the involvement of antibodies and complement activation in this process.


RESULTS
Pneumococci are able to bind to human red blood cells in the presence of human serum. Coating with C3b/C4b appeared obligatory for pneumococcal adherence to red blood cells. The ligand on erythrocytes was confirmed to be complement receptor 1. Kinetic studies showed that innate (mannose-binding lectin) and specific immune factors (IgG antibodies) contributed to the binding of C3b-coated pneumococci to human erythrocytes. After initial binding, serum-derived factor I was found to induce bacterial detachment from the erythrocyte.


CONCLUSIONS
Pneumococci are able to adhere to red blood cells. Both the classical and lectin complement pathways are important for optimal C3b-coating of pneumococci for immune adherence. Bound pneumococci are detached from red blood cells by factor I. These findings are in line with the hypothesis of immune adherence in which human erythrocytes are able to bind pneumococci and target the bacteria to the reticulo-endothelial system in the spleen.
Hament
J-M
JM
Department of Paediatric Infectious Diseases, Wilhelmina Children's Hospital, University Medical Centre, Utrecht, The Netherlands.
van Dijk
H
H
Fleer
A
A
Aerts
P C
PC
Schoenmakers
M
M
de Snoo
M W
MW
Dekker
B H A Th
BH
Kimpen
J L L
JL
Wolfs
T F W
TF
D001422:Bacterial Adhesion / Q000276:immunology*; D002448:Cell Adhesion / Q000276:immunology; D003167:Complement Activation / Q000276:immunology; D003179:Complement C3b / Q000276:immunology; D015935:Complement C4b / Q000276:immunology; D017244:Complement Factor I / Q000276:immunology; D004912:Erythrocytes / Q000276:immunology*; D005434:Flow Cytometry; D006801:Humans; D007104:Immune Adherence Reaction; D007074:Immunoglobulin G; D037601:Mannose-Binding Lectin / Q000276:immunology; D011951:Receptors, Complement / Q000276:immunology; D013296:Streptococcus pneumoniae / Q000276:immunology*
D007074:Immunoglobulin G; D037601:Mannose-Binding Lectin; D011951:Receptors, Complement; D003179:Complement C3b; D015935:Complement C4b; D017244:Complement Factor I