En. Klyushnenkova et al., CD48 DELIVERS AN ACCESSORY SIGNAL FOR CD40-MEDIATED ACTIVATION OF HUMAN B-CELLS, Cellular immunology, 174(1), 1996, pp. 90-98
CD48, a glycosyl phosphatidylinositol anchored molecule has recently b
een shown to be a ligand for the T cell surface protein CD2 in mouse,
human, and rat. It is expressed on practically all human T and B cells
; however, its function remains unknown. We examined whether CD48 may
be involved in the delivery of activating signals to human B cells. Co
stimulation with anti-CD48 J4-57 significantly increased CD40-mediated
activation of tonsillar B cells. Costimulatory effect of anti-CD48 wa
s observed on B cell aggregation, proliferation, and IgG secretion, An
ti-CD48 alone did not stimulate resting B cells. Accessory signal prov
ided through CD48 required the presence of IL-4 and/or IL-10, whereas
responses of B cells to IL-2 was not affected. Ligation of CD48 by spe
cific antibody induced CD23 expression on IL-4-stimulated Ramos B cell
line but did not affect expression of CD25, We also examined the bioc
hemical nature of the costimulatory effect of anti-CD40 and CD48. Liga
tion of CD40 or CD48 on the B cells induced tyrosine phosphorylation o
f proteins. CD40 induced earlier changes in the protein phosphorylatio
n than CD48 did, Taken together, our data suggest that the stimulation
via CD40 provides initial signals to activate B cells and CD48 may be
involved in enhancing the activating signal to B cells, resulting in
increased responsiveness of B cells to IL-4 and IL-10. (C) 1996 Academ
ic Press, Inc.