Exocytosis of specific granule lumen proteins

Secondary (specific) granules are peroxidase-negative and rich in antimicrobial substances (Joiner et al. 1989, Rorvig et al. 2012). They are more irregular and elongated in form than azurophil granules (Bainton et al. 1971). This might reflect volume adjustment in azurophil granules, which are known to proteolytically process a significant fraction of the proteins that are targeted to them, while little or no processing and therefore no increase in osmotic activity due to proteolysis has been observed in secondary granules (Borregaard & Cowland 1997). Secondary and tertiary granules have overlapping contents but can be discriminated by their intrinsic buoyant densities when centrifuged on gradient media (Kjeldsen et al. 1994).

次级（特定）颗粒呈过氧化物酶阴性，富含抗菌物质（Joiner 等人，1989；Rorvig 等人，2012）。其形态相较于天青颗粒更为不规则且细长（Bainton 等人，1971）。这或许反映了天青颗粒在体积上的调整，后者已知能通过蛋白水解作用处理大量被靶向至其处的蛋白质，而次级颗粒则观察到的蛋白水解作用微乎其微，或根本无此作用，因此蛋白水解导致的渗透活性增加也未见明显（Borregaard 与 Cowland，1997）。次级颗粒与三级颗粒内容存在重叠，但可通过在梯度介质离心时其内在浮力密度进行区分（Kjeldsen 等人，1994）。