Requirements for antigen presenting cells in the class II MHC-restricted mixed lymphocyte reaction

Abstract

대식세포, 수지상세포, B 세포 등은 CD4^(+) T 세포에 대한 항원 제공 세포로 알려져 있다. 이들 항원 제공 세포는 T 림프구를 활성화시키는 역량에 있어 차이가 있다. 특히 B 세포의 class Ⅱ MHC 분자는 여러 항원 제공 세포와 달리 당화되는 정도가 매우 높은 것으로 알려져 있다. 본 연구에서는 림프구 혼합반응을 이용하여 B 세포에 neuraminidase를 처리하여, 항원 제공에 대한 영향을 살펴보았고 그 효소의 작황 기전에 대하여 연구하였다. B 세포를 neuraminidase고 처리하였을 때 CD4^(+) T 세포의 증식은 철저하게 증가하였다. 또한, CD4^(+) T 세포만을 neuraminidase로 처리하여 항원 제공 세포와 반응시켰을 때, 림프구 혼합 반응은 증가하였다. 림프구 혼합 반응 증가 결과는 세포간의 접촉을 유도하는 ployethylene glycol에 의해서도 얻어졌다. 이는 neuraminidase에 의해 sialic acid가 제기됨으로 인해 작용 세포들의 세포 반발 작용을 저하시킴으로써 세포간의 접촉을 향상한 작용 기전을 제시하고 있다. 한편 CD4^(+) T 세포에 neuraminidase로 처리하였을 때, phorbol myristate acetate와 함께 배양시 neuraminidase를 처리하지 않은 대조군에 비해 세포 증식의 항상과 세포내 Ca^(2+) 농도 증가를 flow cytometry에 의해 확인하였다. 이로써 neuraminidase 처리 그 자체가 세포내 Ca^(2+) 유통을 유발함으로써 CD4^(+) T 세포에 활성 신호 전달에 관여함을 제시하고 있다.;A successful T cell immune response requires biological signals provided by antigen presenting cells (APC). Many cell types including dendritic cells, macrophages, epidermal Langerhans cells and B cells have been implicated as APC for CD4^(+) T cells. The various APC have different capacity to stimulate CD4^(+) T cells. It has been suggested that modification of carbohydrate moiety in the class Ⅱ MHC molecules might be responsible for the different APC capacity. It has been found that the class Ⅱ MHC molecules of resting B cells are differentially glycosylated among various APC. To address the requirements of APC to stimulate CD4^(+) T cells, B cells whose surface glycosylation were lowered were examined for their APC function in mixed lymphocyte reaction (MLR). Thus, when B cells were treated with neuraminidase before they were subjected to reaction with responder T cells, proliferation of CD4^(+) T cells was markedly enhanced in MLR. Furthermore, neuraminidase-treated CD4^(+) T cells recognized the untreated B cells in a much greater extent than untreated responder cells. An MLR enhancing effect similar to that obtained by neuraminidase treament could be obtained by the addition of 2% polyethylene glycol, enhancing cell-cell adhesiveness, to the MLR culture. These results suggest that removal of negatively-charged sialic acid by neuraminidase treatment, thereby reducing the net charge on either of stimulator cells or responder cells, results in an enhanced cell-cell interaction that is critical for T cell stimulation. In addition, neuraminidase treatment of respondlng CD4^(+) T cells showed significant proliferation in synergy with phorbol myristate acetate (PMA) and resulted in an increasement of intracellular free calcium. These results demonstrate that neuraminidase treatment itself appears to trigger activation signal(s) in the responding CD4^(+) T cells presumably by mobilizing intracellular calcium.