Filamentous hemagglutinin is an adhesin protein produced by Bordetella pertussis, the bacterium responsible for whooping cough. It plays a crucial role in the pathogenesis of the disease by facilitating the attachment of the bacteria to the ciliated epithelial cells of the respiratory tract, leading to respiratory symptoms. Understanding filamentous hemagglutinin is essential for developing effective vaccines and treatments, as it is a key target for immunological responses in pertussis.