Eur J Immunol. 1994 Dec;24(12):2993-9. Unique Identifier : AIDSLINE
During cognate B:T interactions, B cells encounter antigen (Ag) through
surface immuno-globulin (sIg) and present antigenic peptides to T helper
(Th) cells. However, most in vitro systems used to study contact events
involved in the delivery of T help for B cells circumvent the
requirement for T cell Ag specificity by using anti-CD3/T cell receptor
(TcR) monoclonal antibodies (mAb) to activate T cells. To study the role
of sIg engagement in the responsiveness of B cells to T help, we
pre-treated small resting B cells with soluble anti-kappa mAb prior to
contact with an activated Th1 clone. By reducing the concentration of
anti-TcR mAb we obtained low levels of CD40 ligand (CD40Llow) on Th
cells, comparable to those expressed by lymph node T cells activated in
vitro (ex vivo T cells). In contrast to untreated B cells, which did not
respond to CD40Llow Th, anti-Ig-treated B cells responded strongly. Low
buoyant density B cells also responded to CD40Llow Th cells. There was
no B cell response to resting Th cells. mAb against CD54/intercellular
adhesion molecule-1 or major histocompatibility complex (MHC) class II
completely inhibited B cell responses to CD40Llow Th1 cells, equivalent
to the effects of blocking CD40 interactions. This contrasts with mAb
blocking responses to CD40Lhigh Th, where CD40 effects predominate. Our
data show that sIg engagement is necessary for the induction of B cell
response to CD40Llow Th cells. Anti-CD3-activated ex vivo T cells that
were also CD40Llow did not provide help to small resting B cells, but
did induce responses from sIg-stimulated B cells. Thus, our data support
a requirement for sIg signaling in physiological B cell activation, and
further confirm previous work showing CD40 ligation to be necessary but
not sufficient for delivery of T help to B cells.
Animal B-Lymphocytes/*IMMUNOLOGY Cells, Cultured Female
Histocompatibility Antigens Class II/IMMUNOLOGY Immunoglobulins,
Surface/IMMUNOLOGY In Vitro Intercellular Adhesion
Molecule-1/IMMUNOLOGY *Lymphocyte Cooperation *Lymphocyte
Transformation Membrane Glycoproteins/*IMMUNOLOGY Mice Mice, Inbred
C57BL Receptors, Antigen, B-Cell/*IMMUNOLOGY Signal Transduction
Support, Non-U.S. Gov't T-Lymphocyte Subsets/*IMMUNOLOGY Th1
Cells/IMMUNOLOGY JOURNAL ARTICLE