Pertactin is a protein associated with a specific bacterial species. It plays a role in how the organism interacts with its host. Understanding this protein provides insight into bacterial function and strategies for managing associated diseases.
Understanding Pertactin
Pertactin is a protein found on the outer surface of Bordetella pertussis, the bacterium responsible for whooping cough. This protein is classified as an outer membrane protein and an autotransporter, meaning it facilitates its own transport to the bacterial surface. It has a molecular weight of approximately 69 kilodaltons (kDa).
The structure of pertactin includes beta-helix repeats that protrude from the cell surface. Within these loops, specifically in region 1 (R1), there is an Arg-Gly-Asp (RGD) domain. This RGD domain is believed to aid in binding to integrins on host cell membranes, facilitating bacterial adhesion. Pertactin’s presence on the bacterial surface makes it accessible for interaction with the host environment.
Pertactin’s Contribution to Whooping Cough
Pertactin functions as a virulence factor, which means it helps Bordetella pertussis cause disease. Its primary role is in helping the bacteria attach to host cells, particularly the ciliated epithelial cells lining the respiratory tract. This adherence is a fundamental step for the bacterium to establish an infection and colonize the upper respiratory system.
Beyond adhesion, pertactin also contributes to the bacterium’s ability to evade the host’s immune system. It helps Bordetella species resist clearance by neutrophils, a type of immune cell. This resistance allows the bacteria to persist and multiply within the respiratory tract, leading to the characteristic symptoms of whooping cough. The coordinated expression of pertactin and other virulence factors allows the bacterium to adapt to the host environment.
Pertactin’s Role in Vaccines
Pertactin is a component in acellular pertussis vaccines, such as DTaP for children and Tdap for adolescents and adults. It was included because it is highly immunogenic, meaning it can effectively stimulate an immune response. The vaccine utilizes purified pertactin from Bordetella pertussis.
When introduced in the vaccine, pertactin acts as an antigen, prompting the immune system to produce antibodies against it. These antibodies recognize and neutralize pertactin on the surface of Bordetella pertussis if the vaccinated individual encounters the bacterium. This antibody production is a primary mechanism by which the vaccine provides protection against whooping cough. Antibody titers to pertactin show increases following primary and booster vaccinations.
Current Challenges with Pertactin
Despite its role in vaccines, challenges have emerged concerning pertactin’s effectiveness. Bordetella pertussis strains deficient in pertactin have become increasingly prevalent, particularly in countries utilizing acellular pertussis vaccines. In some regions, up to 85-90% of circulating strains lack pertactin. This phenomenon is thought to be a result of vaccine-driven evolution, where the bacteria adapt to evade the immunity elicited by vaccines containing pertactin.
The emergence of pertactin-deficient strains has implications for vaccine effectiveness. While current acellular vaccines still offer protection against severe disease, the absence of pertactin in circulating strains may reduce the vaccine’s ability to prevent colonization and transmission. Research indicates that pertactin-deficient strains can induce different immune responses in host cells, suggesting a complex interplay between the evolving pathogen and the host immune response. This ongoing bacterial adaptation presents a challenge for long-term control of whooping cough.