Wilbur S M, Marelli O, Bonavida B
Cancer Res. 1983 Sep;43(9):4266-70.
The reticulum cell sarcomas (RCS) of SJL/J mice are of particular interest since they readily induce the proliferation of syngeneic T-lymphocytes. Previous cellular studies examined the antigens on the RCS which stimulated this response and suggested that the tumor expressed allogeneic I-region-associated (Ia) antigens normally associated with the E alpha:E beta molecular complex (S. M. Wilbur and B. J. Bonavida, Exp. Med., 153: 501-513, 1981). These particular Ia glycoproteins are not expressed on normal SJL/J cells due to a defect in the E alpha polypeptide synthetic pathway. However, the E beta subunit is synthesized normally by these animals but remains intracellular. The SJL/J-derived RCS may circumvent this defect in E alpha subunit biosynthesis. The aberrant synthesis of this polypeptide is thought to allow membrane presentation of an intact pseudoallogeneic Ia glycoprotein which utilized the normally dormant E beta s polypeptide. In the present study, two monoclonal antibodies directed against the Ia.7 specificity of the E alpha chain (13/18, 14-4-4S) were used to examine more directly the expression of this polypeptide on the tumor. Surprisingly, neither antibody was effective against the RCS in a direct complement-mediated cytolysis assay. Nevertheless, the tumor was found to specifically adsorb lytic activity of both the monoclonal antibodies. In addition, both a cold-cell competition assay and indirect immunofluorescence corroborated the data and indicated that the RCS does express detectable levels of the Ia.7 antigen. Normal spleen cells and lipopolysaccharide B-derived blasts from SJL/J mice were found in all experiments to be devoid of any specific reactivity with these monoclonal antibodies. In addition, continued in vivo passage of transplantable RCS was found to cause down-modulation of the Ia.7 specificities on these tumors. Newer RCS transplantable lines, however, expressed demonstrable levels of this alloantigen in both cellular and serological assays. The observed down-modulation could explain the difficulties encountered in defining this specificity on long-term transplantable RCS. In conclusion, the present serological study corroborates the early cell-binding data. An Ia.7 antigen is shown to be expressed on the RCS, yet this specificity could not be detected on normal SJL/J cells.
SJL/J小鼠的网状细胞肉瘤（RCS）特别引人关注，因为它们很容易诱导同基因T淋巴细胞的增殖。先前的细胞研究检测了刺激这种反应的RCS上的抗原，并表明肿瘤表达了通常与Eα:Eβ分子复合物相关的同种异体I区相关（Ia）抗原（S.M.威尔伯和B.J.博纳维达，《实验医学杂志》，153:501-513，1981）。由于Eα多肽合成途径存在缺陷，这些特定的Ia糖蛋白在正常的SJL/J细胞上不表达。然而，这些动物能正常合成Eβ亚基，但它仍留在细胞内。源自SJL/J的RCS可能规避了Eα亚基生物合成中的这一缺陷。这种多肽的异常合成被认为使得完整的假同种异体Ia糖蛋白能够呈现在细胞膜上，该糖蛋白利用了通常处于休眠状态的Eβs多肽。在本研究中，使用了两种针对Eα链Ia.7特异性的单克隆抗体（13/18、14-4-4S）来更直接地检测这种多肽在肿瘤上的表达。令人惊讶的是，在直接补体介导的细胞溶解试验中，这两种抗体对RCS均无效。然而，发现肿瘤能特异性吸附这两种单克隆抗体的溶解活性。此外，冷细胞竞争试验和间接免疫荧光都证实了这些数据，并表明RCS确实表达了可检测水平的Ia.7抗原。在所有实验中都发现，SJL/J小鼠的正常脾细胞和脂多糖B诱导的胚细胞与这些单克隆抗体没有任何特异性反应。此外，发现可移植RCS在体内的持续传代会导致这些肿瘤上Ia.7特异性的下调。然而，更新的可移植RCS系在细胞和血清学检测中都表达了可证实水平的这种同种异体抗原。观察到的下调现象可以解释在长期可移植RCS上定义这种特异性时遇到的困难。总之，本血清学研究证实了早期的细胞结合数据。结果表明，RCS上表达了Ia.7抗原，但在正常的SJL/J细胞上检测不到这种特异性。
