C3 and infection: Infection of ∆2–25 A549 cells expressing this truncated C-terminal C3 fragment also led to bacterial deposition of a C3 fragment similar in size to that deposited by WT or ∆AUG1 cells, (Fig. 6D), confirming that this C-terminal domain of intracellularly expressed C3 α-chain interacts with S. aureus.