Life P, Aubry J P, Estoppey S, Schnuriger V, Bonnefoy J Y
Glaxo Institute for Molecular Biology, Geneva.
Eur J Immunol. 1995 Feb;25(2):333-9. doi: 10.1002/eji.1830250205.
Activated T cells induce IgE switching in B cells via a combination of lymphokines and direct T:B cell contact. As CD28-deficient mice have reduced basal levels of IgG1 and IgG2a and diminished Ig class switching, we investigated whether the CD28/B7.1 (CD80) ligand pairing might also be involved in human IgE regulation. Co-incubation of an allergen-specific, human T cell clone with tonsillar B cells caused a marked up-regulation of CD28 expression, whereas, in contrast, CD45 RB expression was unaffected. To test whether blocking the CD28: B7.1 interaction affected IgE synthesis, a dialyzed anti-CD28 monoclonal antibody (mAb) was added to cultures containing tonsillar B cells, pre-activated T cell clones and interleukin-4. Anti-CD28 treatment caused a reproducible, dose-dependent inhibition of IgE, but not IgG synthesis that was accompanied by a visible decrease in cell aggregate formation. Conversely, an anti-B7.1 mAb had no effect in this system. The effect of blocking CD28-ligand interactions on lymphocyte adhesion was formally assessed on human T cell clones and B cell lines using dual intracellular staining and flow cytometry. Co-incubation with an anti-CD28 mAb, but not control IgG or anti-B7.1 mAb, resulted in a marked impairment of conjugate formation that correlated well with T cell surface expression of CD28. Using this system we found that an anti-CTLA-4 mAb but not an anti-B7.2 mAb inhibited T:B cell conjugate formation. Lastly, in addition to a direct effect of anti-CD28 mAb on conjugate formation, 14-day culture of T and B cells in the presence of anti-CD28 caused a marked decrease of ICAM-1 (CD54) expression on aggregated lymphocytes. In contrast, LFA-1 (CD18) expression was unaffected. We, therefore, conclude that the T cell co-stimulatory molecule CD28 is involved in the regulation of IgE synthesis in vitro. CD28 may act to a limited extent as an adhesion molecule, though apparently not by pairing with B7.1 or B7.2. It is more likely that ligation of CD28 under certain conditions modulates the expression of other T and B cell surface molecules.
活化的T细胞通过多种淋巴因子以及T细胞与B细胞的直接接触诱导B细胞发生IgE类别转换。由于CD28缺陷小鼠的IgG1和IgG2a基础水平降低且Ig类别转换减少，我们研究了CD28/B7.1（CD80）配体对是否也参与人类IgE的调节。将过敏原特异性的人类T细胞克隆与扁桃体B细胞共同孵育，导致CD28表达显著上调，而相比之下，CD45 RB表达未受影响。为了测试阻断CD28:B7.1相互作用是否会影响IgE合成，将透析后的抗CD28单克隆抗体（mAb）添加到含有扁桃体B细胞、预激活的T细胞克隆和白细胞介素-4的培养物中。抗CD28处理导致IgE合成出现可重复的、剂量依赖性抑制，但不影响IgG合成，同时细胞聚集体形成明显减少。相反，抗B7.1 mAb在该系统中没有作用。使用双重细胞内染色和流式细胞术，在人类T细胞克隆和B细胞系上正式评估了阻断CD28配体相互作用对淋巴细胞黏附的影响。与抗CD28 mAb共同孵育，但不与对照IgG或抗B7.1 mAb共同孵育，导致共轭形成显著受损，这与T细胞表面CD28的表达密切相关。使用该系统我们发现，抗CTLA-4 mAb可抑制T:B细胞共轭形成，而抗B7.2 mAb则无此作用。最后，除了抗CD28 mAb对共轭形成的直接作用外，在抗CD28存在的情况下对T细胞和B细胞进行14天培养，导致聚集淋巴细胞上ICAM-1（CD54）表达显著降低。相比之下，LFA-1（CD18）表达未受影响。因此，我们得出结论，T细胞共刺激分子CD28参与体外IgE合成的调节。CD28可能在一定程度上作为黏附分子发挥作用，尽管显然不是通过与B7.1或B7.2配对。更有可能的是，在某些条件下CD28的结合会调节其他T细胞和B细胞表面分子的表达。
