Sanchez-Lockhart Mariano, Miller Jim
David H. Smith Center for Vaccine Biology and Immunology, Aab Institute of Biomedical Sciences and the Department of Microbiology and Immunology, University of Rochester, Rochester, NY 14642, USA.
J Immunol. 2006 Apr 15;176(8):4778-84. doi: 10.4049/jimmunol.176.8.4778.
During T cell activation by APC, CD28 is colocalized with TCR in the central supramolecular activation cluster (cSMAC) region of the immunological synapse. CD28 signaling through PI3K results in the recruitment of protein kinase C (PKC)theta to the cSMAC, activation of NF-kappaB, and induction of IL-2 transcription. These results suggest that localized engagement of CD28 within the cSMAC may be required for CD28 activation and/or signal integration with TCR signals. To test this model we have examined the mechanism of CD28-mediated induction of IL-2 secretion when CD28 is engaged outside of the immunological synapse. CD4 T cells were stimulated with Ag presented by B7-negative APC and CD28 costimulation was provided in trans by anti-CD28-coated beads or by class II-negative, B7-positive cells. We show that induction of IL-2 secretion under these conditions did not require expression of PKCtheta and did not induce NF-kappaB activation or IL-2 transcription. In contrast, CD28 costimulation in trans did induce IL-2 mRNA stability, accounting for the up-regulation of IL-2 secretion. These data indicate that the ability of CD28 to up-regulate IL-2 transcription requires colocalization of TCR and CD28 at the plasma membrane, possibly within the cSMAC of the immunological synapse. In contrast, the ability of CD28 to promote IL-2 mRNA stability can be transduced from a distal site from the TCR, suggesting that signal integration occurs downstream from the plasma membrane. These data support the potential role of trans costimulation in tumor and allograft rejection, but limit the potential functional impact that trans costimulation may have on T cell activation.
在抗原呈递细胞（APC）激活T细胞的过程中，CD28与T细胞受体（TCR）共定位于免疫突触的中央超分子激活簇（cSMAC）区域。通过磷脂酰肌醇-3激酶（PI3K）的CD28信号传导导致蛋白激酶C（PKC）θ募集至cSMAC，激活核因子κB（NF-κB），并诱导白细胞介素-2（IL-2）转录。这些结果表明，cSMAC内CD28的局部结合可能是CD28激活和/或与TCR信号整合所必需的。为了验证该模型，我们研究了CD28在免疫突触之外结合时介导IL-2分泌诱导的机制。用B7阴性的APC呈递的抗原刺激CD4 T细胞，并通过抗CD28包被的珠子或II类阴性、B7阳性细胞进行反式共刺激提供CD28。我们发现，在这些条件下IL-2分泌的诱导不需要PKCθ的表达，也不会诱导NF-κB激活或IL-2转录。相反，反式共刺激确实诱导了IL-2 mRNA的稳定性，这解释了IL-2分泌的上调。这些数据表明，CD28上调IL-2转录的能力需要TCR和CD28在质膜上共定位，可能在免疫突触的cSMAC内。相比之下，CD28促进IL-2 mRNA稳定性的能力可以从远离TCR的位点转导，这表明信号整合发生在质膜下游。这些数据支持了反式共刺激在肿瘤和同种异体移植排斥反应中的潜在作用，但限制了反式共刺激对T细胞激活可能产生的潜在功能影响。
