Endocytosis of beta 2 integrins by stimulated human neutrophils analyzed by flow cytometry.
Flow cytometry and fluorescently labeled monoclonal antibodies were used to investigate endocytosis of human neutrophil beta 2 integrins following cellular activation. CD18 initially present on the cell surface cycled in two phases after exposure to formyl peptide or platelet-activating factor. The first phase lasted 3 min at 37 degrees C; after a lag, CD18 was specifically internalized at approximately 20%/min. Subsequently a second phase was detectable consisting of exponential reduction of internal fluorescence with a half-time of approximately 2 min, representing probe reexpression. At peak endocytosis approximately 40% of CD18 was internalized. All of the internalized CD18 was associated with alpha M (CR3); no endocytosis of alpha L (LFA-1) was observed. When neutrophils were stimulated with phorbol esters or calcium ionophore, CD18 was internalized much more slowly (t1/2 = 5 min) and probe was not reexpressed. Endocytosis of CD18 may participate in regulating neutrophil adhesiveness, removing activated receptors, or permitting receptor recycling.
Chambers
J D
JD
La Jolla Institute for Experimental Medicine, California 92037.
Simon
S I
SI
Berger
E M
EM
Sklar
L A
LA
Arfors
K E
KE
D000911:Antibodies, Monoclonal; D015703:Antigens, CD / Q000032:analysis; D018821:CD18 Antigens; D004705:Endocytosis / Q000187:drug effects; D005434:Flow Cytometry; D006801:Humans; D007140:Immunoglobulin Fab Fragments; D066298:In Vitro Techniques; D016023:Integrins / Q000378:metabolism*; D007700:Kinetics; D016169:Lymphocyte Function-Associated Antigen-1 / Q000378:metabolism; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009504:Neutrophils / Q000187:drug effects / Q000502:physiology*; D016028:Receptors, Leukocyte-Adhesion / Q000378:metabolism*; D015854:Up-Regulation
D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D018821:CD18 Antigens; D007140:Immunoglobulin Fab Fragments; D016023:Integrins; D016169:Lymphocyte Function-Associated Antigen-1; D016028:Receptors, Leukocyte-Adhesion; D009240:N-Formylmethionine Leucyl-Phenylalanine