The role of intercellular contacts in the activation of B lymphocytes by anti-immunoglobulin antibodies
Spieker-Polet, H.; Hagen, K.; Teodorescu, M.
Journal of Immunology 134(5): 2827-2834
1985
ISSN/ISBN: 0022-1767 PMID: 3872324 Document Number: 258727
It has been proposed that anti-Ig antibody activates B cells in a way analogous to the antigens, i.e., it delivers its signal by cross-linking and clustering the Ig receptors on the surface of one cell. However, the cross-linking of different B cells which may deliver to each other a signal has not been considered. Thus, we examined the effect of preventing cell contacts on the response of rabbit B cells to anti-Ig allotype antibody by using a solid agarose medium. First, we examined the 14C-uridine incorporation in liquid medium and in liquid or solid agarose in cultures stimulated with anti-Ig antibody (Ab). The response was high in liquid agarose or liquid medium but was absent when the agarose-containing medium was solidified at the start of the cultures. If the agarose was solidified 6 hr after the start, a good response was obtained. Moreover, if the cells were sedimented at the start before solidifying the agarose-containing medium, a good response was also obtained. Similar results were obtained when T cells were activated by Con A. To examine whether B cells require contacts with other B cells or with non-B cells, we examined their response to anti-Ig Ab in the absence of macrophages or T cells, and found that purified B cells from lymphoid organs or from thoracic duct responded well in the absence of T cells and/or macrophages. The response was also absent when the cells were cultured in agar at a "local" concentration close to 10(8) cell/ml. Also, concentrated supernatants of anti-Ig-stimulated cells did not increase the response to anti-Ig in solid agarose. These two last observations suggest that the lack of response in solid agarose is not due to a lack of diffusible factors or to a lack of feeder cells. Therefore, because the only difference between the cultures that responded to anti-Ig or Con A and those that did not was the distance between the cells, we concluded that the contact between B cells or between T cells is essential to their activation by their respective mitogens. We speculate that the anti-Ig Ab or the antigen cross-links B cells, which then provide each other with the activating signal or with one of the activating signals.