Ligation of CD45 and the isoforms CD45RA and CD45RB accelerates the rate of constitutive apoptosis in human eosinophils.
BACKGROUND
Eosinophils are important effector cells in asthma pathogenesis, and an understanding of the mechanisms involved in eosinophil apoptosis induction might thus be relevant to the resolution of asthmatic inflammation.


OBJECTIVE
Our aim was to determine the role of the common leukocyte antigen CD45 and the isoforms CD45RA, CD45RB, and CD45RO in human eosinophil apoptosis induction.


METHODS
Immmunostaining and flow cytometry were used to assess CD45 and CD45 isoform expression by eosinophils purified with use of density gradients and immunomagnetic negative selection. Apoptosis induction was measured by binding of fluorescein isothiocyanate-labeled annexin V to eosinophils cultured for 20 hours alone or with saturating quantities of mAb against CD45, CD45RA, CD45RB, CD45RO, CD9, CD11b, and isotype-matched controls in the presence or absence of GM-CSF.


RESULTS
Freshly isolated eosinophils had high expression of CD45 and CD45RO, modest expression of CD45RB, and low expression of CD45RA. Eosinophils cultured alone for 20 hours were found to be approximately 20% to 25% apoptotic. Incubation with mAb against CD45, CD45RA, and CD45RB resulted in significant (P <.005) enhancement (>100%) of their constitutive rate of apoptosis. Incubation with CD45RO, CD11b, CD9 mAb, or isotype controls had no significant effect on the rate of eosinophil constitutive apoptosis. The addition of GM-CSF inhibited eosinophil apoptosis but did not prevent CD45, CD45RA, or CD45RB mAb-dependent apoptosis induction.


CONCLUSIONS
These data indicate that ligation of CD45, CD45RA, or CD45RB represents a novel pathway for the induction of apoptosis in human eosinophils.
Blaylock
M G
MG
Department of Medicine and Therapeutics, University of Aberdeen Medical School, Aberdeen, United Kingdom.
Sexton
D W
DW
Walsh
G M
GM
D017209:Apoptosis / Q000276:immunology; D004306:Dose-Response Relationship, Immunologic; D004804:Eosinophils / Q000166:cytology* / Q000502:physiology; D005434:Flow Cytometry; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000494:pharmacology; D006801:Humans; D017493:Leukocyte Common Antigens / Q000096:biosynthesis / Q000502:physiology*; D008026:Ligation; D020033:Protein Isoforms / Q000096:biosynthesis / Q000502:physiology; D013997:Time Factors
D020033:Protein Isoforms; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D017493:Leukocyte Common Antigens