Domenico P, Salo R J, Cross A S, Cunha B A
Infectious Disease Division, Winthrop-University Hospital, Mineola, New York.
Infect Immun. 1994 Oct;62(10):4495-9. doi: 10.1128/iai.62.10.4495-4499.1994.
The polysaccharide capsule of Klebsiella pneumoniae is an important virulence factor that confers resistance to phagocytosis. The treatment of encapsulated bacteria with salicylate to inhibit capsule expression was found to enhance the phagocytosis of encapsulated bacteria by human neutrophils only in the presence of cell surface-specific antibodies. Both type-specific rabbit antisera and anticapsular human hyperimmune globulin were employed as opsonins. Salicylate significantly enhanced phagocytosis with homologous, but not heterologous, whole-cell antisera. Antisera, diluted 1:40, no longer opsonized fully encapsulated bacteria but promoted the uptake of multiple salicylate-treated bacteria in > 90% of neutrophils. Salicylate (0.25 to 1.0 mM) also enhanced opsonization with globulin against homologous bacteria. Higher salicylate levels (1 to 2.5 mM) enhanced the opsonization of heterologous serotypes with human globulin. The nature of antibody attachment to encapsulated bacteria was determined by immunofluorescence. Even after the addition of purified capsular polysaccharide to prevent phagocytosis, K-specific antibodies attached in large amounts to bacteria. K-specific antibodies reacted with antigens throughout the capsule and showed a predilection for a denser inner layer of the capsule, indicating that many of the K-specific antibodies may be masked underneath the capsule surface. K-specific antibodies can also be rendered nonfunctional by soluble, cell-free capsular antigen. In culture, large quantities of soluble capsular polysaccharide extrude from bacteria after overnight growth. The reduction in capsule expression caused by salicylate largely affected the soluble, cell-free fraction. Purified capsular polysaccharide was shown to retard the opsonophagocytosis of salicylate-treated bacteria in a concentration-dependent manner. However, extensive washing of encapsulated bacteria to remove loosely attached capsular material did not significantly enhance opsonophagocytosis. In conclusion, cell-free capsule and cell-associated capsule are antiphagocytic; both act to neutralize K-specific antibodies by binding or concealment. Salicylate-mediated inhibition of capsule expression, particularly of the cell-free fraction, improved K-specific opsonization dramatically.
肺炎克雷伯菌的多糖荚膜是一种重要的毒力因子，可赋予对吞噬作用的抗性。只有在存在细胞表面特异性抗体的情况下，用水杨酸盐处理被包膜细菌以抑制荚膜表达才会增强人中性粒细胞对被包膜细菌的吞噬作用。特异性兔抗血清和抗荚膜人超免疫球蛋白均用作调理素。水杨酸盐能显著增强同源全细胞抗血清介导的吞噬作用，但不能增强异源全细胞抗血清介导的吞噬作用。稀释至1:40的抗血清不再能使完全被包膜的细菌有效调理，但能促进90%以上的中性粒细胞摄取多个经水杨酸盐处理的细菌。水杨酸盐（0.25至1.0 mM）也能增强球蛋白对同源细菌的调理作用。较高浓度的水杨酸盐（1至2.5 mM）能增强人球蛋白对异源血清型的调理作用。通过免疫荧光确定抗体与被包膜细菌结合的性质。即使添加纯化的荚膜多糖以防止吞噬作用，K特异性抗体仍大量附着于细菌。K特异性抗体与整个荚膜中的抗原发生反应，并显示出对荚膜较致密内层的偏好，这表明许多K特异性抗体可能被掩盖在荚膜表面之下。K特异性抗体也可被可溶性无细胞荚膜抗原使其失去功能。在培养过程中，过夜生长后细菌会挤出大量可溶性荚膜多糖。水杨酸盐引起的荚膜表达减少主要影响可溶性无细胞部分。纯化的荚膜多糖以浓度依赖的方式抑制水杨酸盐处理细菌的调理吞噬作用。然而，对被包膜细菌进行广泛洗涤以去除松散附着的荚膜物质并不能显著增强调理吞噬作用。总之，无细胞荚膜和细胞相关荚膜都具有抗吞噬作用；两者都通过结合或隐蔽作用来中和K特异性抗体。水杨酸盐介导的荚膜表达抑制，特别是对无细胞部分的抑制，显著改善了K特异性调理作用。
