C6 and salivary gland disorder: Since C1s is essential for activation of the classical complement pathway, we hypothesize that the complement membrane attack complex plays little or no role in SjS-associated salivary gland disease, a concept supported by the fact that expressions of C6 through C9 transcripts were unchanged, plus the high transcript levels of both Clu (clusterin) and CD59 (protectin), two complement membrane attack complex inhibitors.