Cysteine protease that plays an important role in the inhibition of host innate immune response. Degrades host elastin, fibrogen, fibronectin and kininogen. Blocks phagocytosis of opsonised S. aureus by neutrophils and monocytes by inducing their death in a proteolytic activity-dependent manner. Decreases surface expression of the 'don't eat me' signal CD31 on neutrophils. Cleaves host galectin-3/LGALS3, thereby inhibiting the neutrophil-activating ability of the lectin. Prematurely activated/folded staphopain B is inhibited by staphostatin B (SspC), which is probably required to protect staphylococcal cytoplasmic proteins from degradation by SspB. In the cytoplasm, prematurely activated/folded SspB forms a stable non-covalent complex with SspC. Proteolytically cleaved by staphylococcal serine protease (SspA). The cascade of activation of extracellular proteases proceeds from the metalloprotease aureolysin (aur), through SspA to SspB. Belongs to the peptidase C47 family.