Levitz S M, DiBenedetto D J
Evans Memorial Department of Clinical Research, University Hospital, Boston MA 02118.
J Immunol. 1989 Jan 15;142(2):659-65.
Infections with the encapsulated fungus Cryptococcus neoformans are usually acquired via inhalation, and the presence of a capsule has been identified as a virulence factor. Therefore, we studied murine bronchoalveolar macrophage (BAM)-mediated killing and phagocytosis of encapsulated and acapsular strains of C. neoformans. After 2 h, BAM killed encapsulated strains CN52 and MP415 more readily than acapsular strains CN602 and CAP67 (54.9 and 36.2% vs 26.1 and 6.7%, respectively, p less than 0.001). Pre-incubating CN602 with purified capsular polysaccharide increased killing to 42.7% (p = 0.04). Significantly greater killing of the encapsulated strains also occurred in vivo. BAM-mediated killing of CN52 appeared to proceed by non-oxidative mechanisms, as BAM released minimal amounts of H2O2 after stimulation with CN52, and killing was not reduced by inhibitors or scavengers of the respiratory burst. The association between encapsulation and susceptibility to BAM fungicidal effects was not attributable to differences in yeast ingestion. Using the same low ratio of organisms to BAM as in the killing assay, greater than 95% of both CN52 and CN602 were phagocytosed. However, BAM phagocytosed significantly greater numbers of acapsular CN602 when incubated with a higher inoculum. Phagocytosis and killing of CN52 and CN602 required fresh serum as a source of C. Phagocytosis of CN52, but not CN602, was profoundly inhibited if BAM were plated on surfaces coated with mAb against the C3bR (CR1). mAb against the iC3b receptor (CR3) did not affect phagocytosis of either strain. These data demonstrate the innate ability of BAM to preferentially kill, by apparently non-oxidative mechanisms, an encapsulated as opposed to acapsular organism. Inasmuch as different receptors appear involved in phagocytosis of encapsulated versus acapsular C. neoformans, the disparity in killing may result from the greater ability of receptors mediating uptake of encapsulated organisms to trigger the antimicrobial armamentarium of the BAM.
感染新型隐球菌这种有荚膜的真菌通常是通过吸入获得的，并且已确定荚膜的存在是一种毒力因子。因此，我们研究了小鼠支气管肺泡巨噬细胞（BAM）对新型隐球菌有荚膜菌株和无荚膜菌株的杀伤作用及吞噬作用。2小时后，BAM对有荚膜菌株CN52和MP415的杀伤效果比对无荚膜菌株CN602和CAP67更明显（分别为54.9%和36.2%对26.1%和6.7%，p<0.001）。用纯化的荚膜多糖预孵育CN602后，杀伤率提高到42.7%（p = 0.04）。在体内也观察到对有荚膜菌株的杀伤作用明显更强。BAM对CN52的杀伤作用似乎通过非氧化机制进行，因为在用CN52刺激后，BAM释放的过氧化氢量极少，并且呼吸爆发的抑制剂或清除剂不会降低杀伤作用。荚膜与对BAM杀菌作用的敏感性之间的关联并非归因于酵母摄取的差异。在杀伤试验中使用与生物体和BAM相同的低比例，超过95%的CN52和CN602都被吞噬。然而，当以更高的接种量孵育时，BAM吞噬无荚膜的CN602的数量明显更多。对CN52和CN602的吞噬和杀伤需要新鲜血清作为补体来源。如果将BAM接种在包被有抗C3bR（CR1）单克隆抗体的表面上，CN52的吞噬作用会受到显著抑制，但CN602不受影响。抗iC3b受体（CR3）的单克隆抗体对两种菌株的吞噬作用均无影响。这些数据表明BAM具有通过明显的非氧化机制优先杀伤有荚膜而非无荚膜生物体的天然能力。由于在吞噬有荚膜和无荚膜新型隐球菌时涉及不同的受体，杀伤作用的差异可能是由于介导摄取有荚膜生物体的受体具有更强的能力来触发BAM的抗菌武器库。
