Acquisition of C1 inhibitor by Bordetella pertussis virulence associated gene 8 results in C2 and C4 consumption away from the bacterial surface

Abstract

Whooping cough, or pertussis, is a contagious disease of the respiratory tract that is re-emerging worldwide despite high vaccination coverage. The causative agent of this disease is the Gram-negative Bordetella pertussis. Knowledge on complement evasion strategies of this pathogen is limited. However, this is of great importance for future vaccine development as it has become apparent that a novel pertussis vaccine is needed. Here, we unravel the effect of Virulence associated gene 8 (Vag8) of B. pertussis on the human complement system at the molecular level. We show that both recombinant and endogenously secreted Vag8 inhibit complement deposition on the bacterial surface at the level of C4b. We reveal that Vag8 binding to human C1-inhibitor (C1-inh) interferes with the binding of C1-inh to C1s, C1r and MASP-2, resulting in the release of active proteases that subsequently cleave C2 and C4 away from the bacterial surface. We demonstrate that the depletion of these complement components in the bacterial surrounding and subsequent decreased deposition on B. pertussis leads to less complement-mediated bacterial killing. Vag8 is the first protein described that specifically prevents C1s, C1r and MASP-2 binding to C1-inh and thereby mediates complement consumption away from the bacterial surface. Unravelling the mechanism of this unique complement evasion strategy of B. pertussis is one of the first steps towards understanding the interactions between the first line of defense complement and B. pertussis.

Edwardsiella tarda Tunes Tricarboxylic Acid Cycle to Evade Complement-Mediated Killing

“…They can escape from serum complement-mediated killing that is a rapid and potent measure of innate immunity against bacteria ( 36 , 37 ). So far, three mechanisms have been reported for serum resistance in bacteria: cleavage of complement components with protease; inhibition of complement activation through recruitment of factors such as factor H and C4BP to the bacterial cell surface; and lipopolysaccharide- and capsular polysaccharide-mediated suppression of complement activation ( 38 , 39 ), all of which leads to the failure of MAC formation. Since the three pathways are associated with membrane structures, almost all of the studies investigate the physical nature of outer membrane, and the functions of outer membrane proteins in serum resistance in Gram-negative bacteria ( 40 , 41 ).…”

Bordetella pertussis pertactin knock-out strains reveal immunomodulatory properties of this virulence factor

“…The reason why we chose vag8 to detect the presence of B. pertussis in the lungs of the infected mice is because the gene for this virulence factor is present in Bordetella spp . Recently, we have unraveled the underlying mechanisms of complement evasion by Vag8 of B. pertussis 25 . Thermal cycling parameters consisted of 1 min at 50 °C and 10 min at 95 °C, followed by 40 cycles of 15 s at 95 °C and 1 min at 60 °C using the following primers: Vag8-sense (GGT TCA CTG GTA GAG AGC AC), Vag8-anti-sense (GTT GAG CAG GGA CAC ATT AC), murine GAPDH-sense (TGC ACC ACC AAC TGC TTA G) and murine GAPDH-anti-sense (GGA TGC AGG GAT GAT GTT C).…”

Localization of regions of aBordetella pertussisautotransporter, Vag8, interacting with C1 inhibitor

“…After passing through the inner membrane by a canonical secretion system, the passenger domain is translocated across the outer membrane by the translocator domain. The passenger domain of Vag8 is cleaved and liberated into the extracellular milieu (5). In B. pertussis infection, the liberated Vag8 binds and inactivates the complement regulating factor, C1 inhibitor (C1 Inh), which inhibits serine proteases involved in the complement system and the plasma kallikrein (PK)-kinin system (6), and plays a role in evasion of the complement system and activation of the contact system by the bacterium (5, 7, 8).…”