Immunoglobulin signal transduction guides the specificity of B cell-T cell interactions and is blocked in tolerant self-reactive B cells.
The specificity of antibody (Ab) responses depends on focusing helper T (Th) lymphocyte signals to suitable B lymphocytes capable of binding foreign antigens (Ags), and away from nonspecific or self-reactive B cells. To investigate the molecular mechanisms that prevent the activation of self-reactive B lymphocytes, the activation requirements of B cells specific for the Ag hen egg lysozyme (HEL) obtained from immunoglobulin (Ig)-transgenic mice were compared with those of functionally tolerant B cells isolated from Ig-transgenic mice which also express soluble HEL. To eliminate the need for surface (s)Ig-mediated Ag uptake and presentation and allow the effects of sIg signaling to be studied in isolation, we assessed the ability of allogeneic T cells from bm12 strain mice to provide in vivo help to C57BL/6 strain-transgenic B cells. Interestingly, non-tolerant Ig-transgenic B cells required both allogeneic Th cells and binding of soluble HEL for efficient activation and Ab production. By contrast, tolerant self-reactive B cells from Ig/HEL double transgenic mice responded poorly to the same combination of allogeneic T cells and soluble HEL. The tolerant B cells were nevertheless normally responsive to stimulation with interleukin 4 and anti-CD40 Abs in vitro, suggesting that they retained the capacity to respond to mediators of T cell help. However, the tolerant B cells exhibited a proximal block in the sIg signaling pathway which prevented activation of receptor-associated tyrosine kinases in response to the binding of soluble HEL. The functional significance of this sIg signaling defect was confirmed by using a more potent membrane-bound form of HEL capable of triggering sIg signaling in tolerant B cells, which markedly restored their ability to collaborate with allogeneic Th cells and produce Ab. These findings indicate that Ag-specific B cells require two signals for mounting a T cell-dependent Ab response and identify regulation of sIg signaling as a mechanism for controlling self-reactive B cells.
Cooke
M P
MP
Howard Hughes Medical Institute, Stanford University, California 94305.
Heath
A W
AW
Shokat
K M
KM
Zeng
Y
Y
Finkelman
F D
FD
Linsley
P S
PS
Howard
M
M
Goodnow
C C
CC
D000818:Animals; D000941:Antigens / Q000276:immunology; D001402:B-Lymphocytes / Q000276:immunology / Q000378:metabolism / Q000502:physiology*; D002450:Cell Communication; D002462:Cell Membrane / Q000201:enzymology; D002478:Cells, Cultured; D007108:Immune Tolerance; D007072:Immunoglobulin D / Q000276:immunology; D007075:Immunoglobulin M / Q000276:immunology; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009113:Muramidase / Q000378:metabolism; D011947:Receptors, Antigen, B-Cell / Q000378:metabolism*; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000276:immunology / Q000378:metabolism / Q000502:physiology*
D000941:Antigens; D007072:Immunoglobulin D; D007075:Immunoglobulin M; D011947:Receptors, Antigen, B-Cell; D009113:Muramidase