Brown M L, Fields P E, Kurlander R J
Department of Medicine, Duke University Medical Center, Durham, NC 27710.
J Immunol. 1992 Jan 15;148(2):555-61.
Though ingested Ag are readily degraded into peptides within endocytic vesicles, APC usually cannot present these fragments to CD8 cells. Despite this generalization, some exceptions have been noted. For example, murine macrophage targets readily process heat-killed Listeria monocytogenes (HKLM) into a form recognizable by immune CD8 CTL. Using an assay of Listeria-specific, CD8-mediated cytotoxicity to quantitate Ag presentation by C57Bl/6 macrophage targets, we have examined some of the cellular requirements for this form of Ag processing. To assess whether the physical form of the Ag is an important determinant of processing, we compared the ability of macrophages to present intact HKLM, fractionated L. monocytogenes (LM) membranes, and octyl-beta-d-thioglucopyranoside-solubilized extracts of LM membranes. Macrophages presented each Ag form in a similar manner indicating that processing is not critically dependent on the presence of intact bacteria or even on the introduction of Ag in a particulate form. To gain insight into the metabolic requirements for Ag processing, we examined the effects of several inhibitors. As might be expected, listerial Ag presentation was blocked by brefeldin, a known inhibitor of the endogenous pathway of Ag processing. LM Ag presentation, however, was also blocked by inhibitors of endosomal acidification (chloroquine, ammonium chloride, and monensin) and by the acid protease inhibitor pepstatin A, suggesting that endocytic processing may play an essential role in CD8 recognition of this Ag. To formally establish that this pattern of exogenous Ag processing requires the presence of a class I MHC product, we demonstrated that beta-2 microglobulin-deficient macrophages, which lack class I MHC product expression, cannot present HKLM to CD8 cells. However, we could not block Ag presentation by incubating macrophages with monoclonal anti-H-2K or H-2D antibodies, suggesting that LM Ag presentation may be mediated by some other class I MHC product. Additional characterization of this pathway of Ag presentation is warranted in view of its possible role in initiating CD8-mediated immunity against microbial Ag.
尽管摄入的抗原（Ag）很容易在内吞小泡内降解为肽段，但抗原呈递细胞（APC）通常无法将这些片段呈递给CD8细胞。尽管有这一普遍规律，但也有一些例外情况被注意到。例如，小鼠巨噬细胞靶标能轻易地将热灭活的单核细胞增生李斯特菌（HKLM）加工成可被免疫CD8细胞毒性T淋巴细胞（CTL）识别的形式。利用李斯特菌特异性、CD8介导的细胞毒性检测来定量C57Bl/6巨噬细胞靶标的抗原呈递，我们研究了这种抗原加工形式的一些细胞需求。为了评估抗原的物理形式是否是加工的重要决定因素，我们比较了巨噬细胞呈递完整HKLM、单核细胞增生李斯特菌（LM）分级分离的膜以及LM膜的辛基-β-D-硫代葡萄糖苷溶解提取物的能力。巨噬细胞以相似的方式呈递每种抗原形式，这表明加工并不关键地依赖于完整细菌的存在，甚至也不依赖于以颗粒形式引入抗原。为了深入了解抗原加工的代谢需求，我们研究了几种抑制剂的作用。正如预期的那样，布雷菲德菌素（一种已知的抗原加工内源性途径抑制剂）阻断了李斯特菌抗原呈递。然而，LM抗原呈递也被内体酸化抑制剂（氯喹、氯化铵和莫能菌素）以及酸性蛋白酶抑制剂胃蛋白酶抑制剂A阻断，这表明内吞加工可能在CD8对这种抗原的识别中起重要作用。为了正式确定这种外源性抗原加工模式需要I类主要组织相容性复合体（MHC）产物的存在，我们证明了缺乏I类MHC产物表达的β2微球蛋白缺陷型巨噬细胞不能将HKLM呈递给CD8细胞。然而，我们不能通过用单克隆抗-H-2K或H-2D抗体孵育巨噬细胞来阻断抗原呈递，这表明LM抗原呈递可能由某些其他I类MHC产物介导。鉴于其在启动针对微生物抗原的CD8介导的免疫中的可能作用，有必要对这种抗原呈递途径进行进一步的表征。
