Takahama Y, Ono S, Ishihara K, Muramatsu M, Hamaoka T
Biomedical Research Center, Osaka University Medical School, Japan.
Eur J Immunol. 1989 Dec;19(12):2227-35. doi: 10.1002/eji.1830191208.
Polyclonal differentiation of unprimed B cells into IgM-producing cells induced by lipopolysaccharide (LPS) or T cell-derived lymphokine B151-TRF2 has been shown to contain a process of I-A-restricted B-B cell interaction, so that the B cell responses are inhibited by monoclonal antibodies (mAb) specific for I-A molecules. On the other hand, the B cell responses are also inhibited by anti-I-E mAb, although I-E molecules are not involved in such B-B cell interaction. In this study, we examined the mechanism underlying the anti-I-E-mediated inhibition of the B cell responses. The B cell responses induced by LPS or B151-TRF2 were inhibited by either anti-I-A or anti-I-E mAb added on day 0 over a 5-day culture period, whereas when added on day 3 the responses were inhibited only by anti-I-E mAb and not by anti-I-A mAb. To gain insight into the mechanism underlying the anti-I-E-mediated inhibition, we prepared monovalent Fab and divalent F(ab')2 fragments of anti-I-A and anti-I-E mAb and examined their effects on the B cell responses. We found that the B cell responses were inhibited by the F(ab')2 but not Fab fragment of anti-I-E mAb, whereas the Fab fragment of anti-I-A mAb still gave effective inhibition. The F(ab')2 but not Fab fragment of anti-I-E mAb induced increases in cyclic AMP (cAMP) levels in B cells, whereas the undigested anti-I-A mAb did not induce such increases. Furthermore, adenylate cyclase inhibitors, which inhibit cellular cAMP accumulation, circumvented the B cell responses inhibited by anti-I-E but not anti-I-A mAb. Thus, these results indicate that the anti-I-E-mediated inhibition of the B cell responses requires increases in intracellular cAMP levels induced by cross-linking of I-E molecules. In contrast, anti-I-A mAb inhibits the B cell responses without cross-linking of I-A molecules and cAMP accumulation. These results reinforce a unique function of I-A molecules as restriction elements in the Ia-restricted B-B cell interaction.
脂多糖（LPS）或T细胞衍生的淋巴因子B151-TRF2诱导未致敏B细胞多克隆分化为产生IgM的细胞，已证明该过程包含I-A限制性B-B细胞相互作用，因此B细胞反应受到针对I-A分子的单克隆抗体（mAb）的抑制。另一方面，B细胞反应也受到抗I-E mAb的抑制，尽管I-E分子不参与这种B-B细胞相互作用。在本研究中，我们研究了抗I-E介导的B细胞反应抑制的潜在机制。在5天的培养期内，第0天添加的抗I-A或抗I-E mAb可抑制LPS或B151-TRF2诱导的B细胞反应，而在第3天添加时，反应仅受到抗I-E mAb的抑制，而不受抗I-A mAb的抑制。为了深入了解抗I-E介导的抑制机制，我们制备了抗I-A和抗I-E mAb的单价Fab片段和二价F(ab')2片段，并研究了它们对B细胞反应的影响。我们发现，抗I-E mAb的F(ab')2片段而非Fab片段可抑制B细胞反应，而抗I-A mAb的Fab片段仍能有效抑制。抗I-E mAb的F(ab')2片段而非Fab片段可诱导B细胞中环状AMP（cAMP）水平升高，而未消化的抗I-A mAb则不会诱导这种升高。此外，抑制细胞cAMP积累的腺苷酸环化酶抑制剂可规避抗I-E而非抗I-A mAb抑制的B细胞反应。因此，这些结果表明，抗I-E介导的B细胞反应抑制需要I-E分子交联诱导细胞内cAMP水平升高。相比之下，抗I-A mAb在不交联I-A分子和不积累cAMP的情况下抑制B细胞反应。这些结果强化了I-A分子作为Ia限制性B-B细胞相互作用中的限制元件的独特功能。
