- The acylated form of protein D of Haemophilus influenzae is more immunogenic than the nonacylated form and elicits an adjuvant effect when it is used as a carrier conjugated to polyribosyl ribitol phosphate. Akkoyunlu, M., Melhus, A., Capiau, C., van Opstal, O., Forsgren, A. Infect. Immun. (1997)