Ledbetter J A, June C H, Rabinovitch P S, Grossmann A, Tsu T T, Imboden J B
Oncogen, Seattle, WA.
Eur J Immunol. 1988 Apr;18(4):525-32. doi: 10.1002/eji.1830180406.
The binding of antibody to the CD4 molecule inhibits mobilization of cytoplasmic free calcium ([Ca2+]i) in response to CD3 cross-linking on resting T cells. Similarly, when CD3 and CD4 are independently and simultaneously cross-linked, calcium mobilization is inhibited when compared to that induced by cross-linking CD3 alone. In contrast, when anti-CD4 and anti-CD3 are cross-linked together, calcium mobilization is substantially higher than from CD3 cross-linking alone. A heteroconjugate consisting of covalently bound CD3 and CD4 monoclonal antibodies (mAb) retains the ability to mobilize [Ca2+]i in CD4 cells at protein concentrations approximately two orders of magnitude lower than the free CD3 mAb, and the activity of the heteroconjugate is inhibitable by free CD4 mAb. The CD3/CD4 heteroconjugate also shows significantly greater activity in stimulation of inositol phosphate IP1, IP2 and IP3 synthesis in T cells than the CD3 mAb alone, and again the activity is inhibited by free CD4 mAb. The activity of the CD3/CD4 heteroconjugate is not simply due to oligomerization, since CD3/CD3 or CD4/CD4 homoconjugates or homoconjugate mixtures did not show increased activity. Other heteroconjugates (CD3/CD5 and CD3/CD28) were not different than the CD3/CD3 homoconjugate in their ability to increase [Ca2+]i. Purified CD4 T cells that do not respond to CD3 mAb in solution do respond to the CD3/CD4 heteroconjugate in solution by proliferating in the presence of a CD28 mAb, with a significant fraction of CD4 cells entering the second cycle within the first three days of stimulation. The CD3/CD4 heteroconjugate co-modulates the CD3 and CD4 receptors, indicating that the heteroconjugate is not simply anchoring the T cell receptor to the T cell surface like anti-CD3 on a solid surface. These results suggest that CD4 plays an active role in signal transduction when brought into close physical proximity to the CD3/T cell receptor complex during major histocompatibility complex class II-restricted antigen presentation.
抗体与CD4分子的结合可抑制静息T细胞上因CD3交联而引起的细胞质游离钙（[Ca2+]i）的动员。同样，当CD3和CD4独立且同时交联时，与单独交联CD3相比，钙动员受到抑制。相反，当抗CD4和抗CD3一起交联时，钙动员比单独交联CD3时显著更高。由共价结合的CD3和CD4单克隆抗体（mAb）组成的异源共轭物在蛋白质浓度比游离CD3 mAb低约两个数量级时，仍保留在CD4细胞中动员[Ca2+]i的能力，并且异源共轭物的活性可被游离CD4 mAb抑制。CD3/CD4异源共轭物在刺激T细胞中肌醇磷酸IP1、IP2和IP3合成方面也比单独的CD3 mAb表现出显著更高的活性，并且该活性同样被游离CD4 mAb抑制。CD3/CD4异源共轭物的活性并非简单地归因于寡聚化，因为CD3/CD3或CD4/CD4同源共轭物或同源共轭物混合物并未表现出活性增加。其他异源共轭物（CD3/CD5和CD3/CD28）在增加[Ca2+]i的能力方面与CD3/CD3同源共轭物没有差异。在溶液中对CD3 mAb无反应的纯化CD4 T细胞在存在CD28 mAb的情况下，通过增殖对溶液中的CD3/CD4异源共轭物有反应，相当一部分CD4细胞在刺激的前三天内进入第二个周期。CD3/CD4异源共轭物共同调节CD3和CD4受体，表明异源共轭物不像固体表面上的抗CD3那样简单地将T细胞受体锚定在T细胞表面。这些结果表明，在主要组织相容性复合体II类限制的抗原呈递过程中，当CD4与CD3/T细胞受体复合物紧密物理接近时，它在信号转导中发挥积极作用。
