Spencer J S, Kubo R T
Department of Medicine, National Jewish Center for Immunology and Respiratory Medicine, Denver, Colorado 80206.
J Exp Med. 1989 Mar 1;169(3):625-40. doi: 10.1084/jem.169.3.625.
The structures of Ia molecules expressed by two BALB/c B cell lymphoma lines, A20-1.11 (A20) and 2PK3, were analyzed in an effort to explain the differences in antigen-presenting capacity displayed by these cells. Alloreactive T cell hybridomas specific for I-Ad and antigen-specific, I-Ad-restricted T cells responded well to A20 as the APC. The same alloreactive T cell hybridomas responded weakly or not at all to 2PK3 and the responses of the antigen-specific, I-Ad-restricted T cells were consistently lower to antigen presented by 2PK3 as compared with A20. T cells restricted to I-Ed responded equally well to either A20 or 2PK3 as APC. Additionally 2PK3, but not A20, stimulated a strong syngeneic mixed lymphocyte response. Structural analyses of the Ia antigens revealed that I-A and I-E molecules were expressed by A20, whereas an I-E and a novel I-A-like molecule were expressed by 2PK3. The novel class II molecule was affinity purified from 2PK3 cells using an mAb specific for Ad beta (MK-D6), and this molecule was subsequently shown by an RIA to react with an E alpha-specific mAb (14-4-4S) as well. Chain-specific polyclonal antisera raised against I-A and I-E alpha and beta chains indicated that the 2PK3 "I-A" alpha chain reacted in immunoblot with E alpha-specific and not A alpha-specific antisera, whereas the beta chain reacted with A beta- and not E beta-specific antisera. Peptide map and partial amino acid sequence analyses indicated that the "I-A" molecule expressed by 2PK3 represented a mixed isotype structure resulting from the pairing of Ed alpha with Ad beta. By immunofluorescence staining analysis, 2PK3 did not react with an mAb specific for Ad alpha. 2PK3 was capable of limited antigen presentation through the mixed isotype molecule to I-Ad-restricted OVA-specific T cell hybridomas, although the responses induced were low compared with presentation through I-A on A20. Previous descriptions of the expression of mixed isotype class II molecules in the mouse have resulted primarily from DNA-mediated gene transfer experiments. The results presented indicate that a mixed isotype class II molecule can be expressed naturally.
为了解释两种BALB/c B细胞淋巴瘤细胞系A20-1.11（A20）和2PK3所表现出的抗原呈递能力差异，对它们所表达的Ia分子结构进行了分析。针对I-Ad的同种异体反应性T细胞杂交瘤以及抗原特异性、I-Ad限制性T细胞对作为抗原呈递细胞（APC）的A20反应良好。相同的同种异体反应性T细胞杂交瘤对2PK3反应微弱或根本无反应，并且与A20相比，抗原特异性、I-Ad限制性T细胞对2PK3呈递的抗原的反应始终较低。受I-Ed限制的T细胞对作为APC的A20或2PK3反应同样良好。此外，2PK3而非A20刺激了强烈的同基因混合淋巴细胞反应。对Ia抗原的结构分析表明，A20表达I-A和I-E分子，而2PK3表达I-E和一种新的I-A样分子。使用针对Adβ的单克隆抗体（MK-D6）从2PK3细胞中亲和纯化出这种新的II类分子，随后通过放射免疫分析（RIA）表明该分子也能与Eα特异性单克隆抗体（14-4-4S）反应。针对I-A和I-E的α链及β链产生的链特异性多克隆抗血清表明，2PK3的“I-A”α链在免疫印迹中与Eα特异性抗血清而非Aα特异性抗血清反应，而β链与Aβ特异性抗血清而非Eβ特异性抗血清反应。肽图和部分氨基酸序列分析表明，2PK3所表达的“I-A”分子代表一种由Edα与Adβ配对产生的混合同种型结构。通过免疫荧光染色分析，2PK3不与针对Adα的单克隆抗体反应。2PK3能够通过混合同种型分子将有限的抗原呈递给I-Ad限制性OVA特异性T细胞杂交瘤，尽管与通过A20上的I-A呈递相比，所诱导的反应较低。此前关于小鼠中混合同种型II类分子表达的描述主要来自DNA介导的基因转移实验。所呈现的结果表明，混合同种型II类分子可以自然表达。
