INVOLVEMENT OF CD23 FC-EPSILON-RII IN THE HOMOTYPIC AND HETEROTYPIC CYTOADHESION OF THE HUMAN EOSINOPHILIC CELL-LINE EOL-3/

A subclone of the EoL-3 human eosinophilic leukemia cell line (EoL-3.1 2) was selected for its high inducibility of CD23 (low affinity IgE re ceptor/Fc epsilon RII) by IL-4, Maximum membrane CD23 expression was d etected after 16 h of incubation with IL-4, then gradually returned to basal level after 48 h, Membrane expression of CD23 on EoL-3.12 cells was found to parallel their homotypic aggregation. Extending the time of incubation with IL-4 to 48 h or more resulted in a de-aggregation of cells with a shedding of membrane CD23 and an increase of its solub le form, sCD23, The IL-4-induced aggregation of EoL-3,12 cells was inh ibited with anti-CD23 antibody or human myeloma IgE protein, indicatin g that it was mediated through the engagement of CD23, EoL3.12 incubat ed with IL-4 displayed morphological changes associated with different iation, such as an increased number of lobulated nuclei with prominent nucleoli, increased ratio of cytoplasm and distinct cytoplasmic proce sses. EoL-3.12 cells incubated with IL-4 also displayed an enhanced ad herence to human umbilical vein endothelial cells (HUVEC), which was r everted when the IL-4 incubation time was extended. Furthermore, the t ransendothelial migration of EoL-3.12 cells toward a chemokinetic grad ient of soluble CD23 (sCD23; 29 kDa fragment) closely paralleled the d ensity of membrane CD23 expressed on EoL-3.12 cells, Additionally, the engagement of CD23 led to the activation of the L-arginine-dependent pathway of nitric oxide (NO) production, as detected by the increase i n intracytoplasmic cGMP concentration. The capacity of EoL-3.12 cells to form homotypic as well as heterotypic adhesion appears therefore to be regulated, at least in part, by the level of CD23 expression.