Haemophilus influenzae serotype a capsular polysaccharide (Hia CPS)

Haemophilus influenzae serotype a capsular polysaccharide (Hia CPS) is a critical virulence factor found on the outer surface of Haemophilus influenzae serotype a bacteria. This polysaccharide capsule acts as a protective layer, shielding the bacterium from the host's immune system by inhibiting processes like complement-mediated lysis and phagocytosis. Structurally, Hia CPS is composed of 4-O-beta-D-glucopyranosyl-D-ribitol residues linked by phosphoric diester bonds between O-4 of D-glucose and O-5 of D-ribitol. Invasive Hia disease, which includes serious conditions such as meningitis, bacteremia, pneumonia, epiglottitis, and septic arthritis, is a significant cause of morbidity and mortality, particularly in young children and indigenous populations. Unlike Haemophilus influenzae type b (Hib), for which highly effective conjugate vaccines exist, there is currently no licensed vaccine specifically targeting Hia CPS. The development of a conjugate vaccine against Hia CPS is considered a priority, as the incidence of invasive Hia disease has been increasing in certain regions. Such a vaccine would aim to induce a robust antibody response against the capsule, thereby providing protective immunity.

Other names

Hia capsuleHia polysaccharide

Haemophilus influenzae serotype a capsular polysaccharide is a key virulence factor. While no specific vaccine targeting Hia CPS is currently available, a vaccine, if developed, would likely be a conjugate vaccine. Such a vaccine would work by inducing the production of specific antibodies against the capsular polysaccharide. These antibodies would then bind to the Hia CPS on the bacterial surface, leading to complement-mediated bacteriolysis and enhanced phagocytosis, thereby clearing the bacteria and providing protection against invasive disease. This mechanism is analogous to that of successful Haemophilus influenzae type b (Hib) conjugate vaccines.