The invention relates to an adjuvant product which is intended to improve the activity of a molecule when administered to a host, characterized in that it comprises at least one part of the P40 protein of Klebsiella pneumoniae or a protein having at least 80% homology with the P40 protein of Klebsiella pneumoniae. The invention also relates to nucleotide sequences which encode these peptides or proteins and to the use of these sequences as a medicament. More particularly, such DNA sequences can be used in compositions which are intended for immunization by the intramuscular or intradermal route.